2023 early spring collaborative pot sampling (CPS1) for Bristol Bay District red king crab

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric

Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric

Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

April 2024

NOAA Technical Memorandum NMFS-AFSC-483

2023 Early Spring Collaborative

Pot Sampling (CPS1) for Bristol

Bay District Red King Crab

(Paralithodes camtschaticus)

T. Loher, B. Daly, S. E. Goodman, M. A. Litzow, A. Nault,

E. R. Ryznar, and L. S. Zacher

The National Marine Fisheries Service's Alaska Fisheries Science Center uses the NOAA Technical

Memorandum series to issue informal scientic and technical publications when complete formal

review and editorial processing are not appropriate or feasible. Documents within this series reect

sound professional work and may be referenced in the formal scientic and technical literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries Science Center continues

the NMFS-F/NWC series established in 1970 by the Northwest Fisheries Center. The NMFS-

NWFSC series is currently used by the Northwest Fisheries Science Center.

This document should be cited as follows:

Loher, T., Daly, B., Goodman, S. E., Litzow, M. A., Nault, A., Ryznar, E. R., and Zacher, L. S. 2024.

2023 early spring collaborative pot sampling (CPS1) for Bristol Bay District red king crab

(Paralithodes camtschaticus). U.S. Department of Commerce, NOAA Technical Memorandum

NMFS-AFSC-483, 66 p.

This document is available online at:

Document available: https://repository.library.noaa.gov

Reference in this document to trade names does not imply endorsement

by the National Marine Fisheries Service, NOAA.

2023 Early Spring Collaborative

Pot Sampling (CPS1) for Bristol

Bay District Red King Crab

(Paralithodes camtschaticus)

T. Loher

, B. Daly

, S. E. Goodman

, M. A. Litzow

, A. Nault

E. R. Ryznar

, and L. S. Zacher

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

NOAA Technical Memorandum NMFS-TM-AFSC-483

April 2024

Bering Sea Fisheries Research Foundation

23929 22nd Dr. SE.

Bothell, WA 98021

Alaska Department of Fish and Game, Westward Region

Division of Commercial Fisheries

351 Research Court

Kodiak, AK 99615

Kodiak Laboratory

Resource Assessment and Conservation Engineering Division

Alaska Fisheries Science Center

National Marine Fisheries Service

National Oceanic and Atmospheric Administration

301 Research Court

Kodiak, AK 99615

iii

ABSTRACT

Between 18 March and 4 April 2023, the Collaborative Pot Sampling (CPS1) project occurred to

collect data on Bristol Bay red king crab (RKC) (Paralithodes camtschaticus). The project

spanned 637 regularly spaced stations placed along 11 transects in Bristol Bay, Alaska. RKC

were fished using modified commercial crab pots (traps) in order to understand early spring

distribution patterns, as well as to collect a suite of biological attributes. A total of 10,191 RKC

were captured at 450 (70.5%) of the survey stations: 76.8% (n = 7,824) of these crabs were male

and 33.2% (n = 2,367) were female. The carapace length (CL) of all RKC was measured and

shell conditions recorded. Females were examined to determine maturity status and the egg

clutches carried by mature females were evaluated for volume and developmental stage. Pop-up

Archival Transmitting tags were deployed on 100 mature-sized male RKC that had recently

molted and were in a new hard-shell condition.

Male RKC ranged from 17.6 to 190.2 mm (0.69 – 7.49 in) CL: 36.1% (n = 2,824) were

immature-sized (< 120 mm (4.7 in) CL); 63.9% (n = 4,999) were mature-sized (≥ 120 mm

(4.7 in) CL); 44.7% (n = 3,497) were legal-sized (≥ 135 mm (5.3 in) CL). Female RKC ranged

from 57.0 to 174.6 mm (2.24 – 6.87 in) CL: 81.7% (n = 1,934) of these individuals were

morphometrically mature. Immature females ranged in size from 57.0 to 99.9 mm (2.24 – 3.93

in) CL and mature females from 82.1 to 174.6 mm (3.23 – 6.87 in) mm CL. No molting males

and only five molting females were captured, the latter of which were all immature. No barren

mature females were encountered. Overall, 43.5% of mature females carried egg clutches that

were approximately three-quarters full and 53.0% carried full clutches.

Spatial distribution of mature-sized males and females did not depart markedly from those

observed during the subsequent (2023) National Marine Fisheries Service trawl survey.

However, for immature crabs of both sexes, the distributions from CPS1 were more similar to

the 2023 trawl survey than to the 2022 trawl survey. For crabs of mature and legal sizes,

distributions observed during CPS1 were less patchy than suggested by the summer trawl survey

data. Across all demographics, the majority of crab were caught within the Nearshore Bristol

Bay Trawl Closure Area (NBBTCA): 66% of all RKC were captured in the NBBTCA and

percentages by demographic ranged from a low of 61.7% for legal-sized males to a high of

75.8% for mature females. For males, just under 20% of individuals were encountered in the Red

King Crab Savings Area (RKCSA). For females, the proportion of crab captured inside the

RKCSA was 17.4% for mature individuals versus 7.6% for immature crabs.

In addition to RKC, 570 Tanner crabs (Chionoecetes bairdi) were captured at 227 stations; 2,393

yellowfin sole (Limanda aspera) were captured at 420 stations; and 1,728 Pacific cod (Gadus

macrocephalus) were captured at 510 stations. Smaller numbers of snow crab (Chionoecetes

opilio), Tanner-snow crab hybrids, horsehair crab (Erimacrus isenbeckii), and Pacific lyre crab

(Hyas lyratus) were encountered, in addition to great sculpin (Myoxocephalus

polyacanthocephalus), walleye pollock (Gadus chalcogrammus), Pacific halibut (Hippoglossus

stenolepis), northern rock sole (Lepidopsetta polyxystra), starry flounder (Platichthys stellatus),

Alaska plaice (Pleuronectes quadrituberculatus), Alaska skate (Bathraja parmifera),

unidentified skates (Rajidae), and sunflowers seastars (Pycnopodia helianthoides). Tags were

deployed on male RKC for 57 – 75 days and had a 91% success rate in providing reliable

locations with minimal error ellipses. There was a high degree of variability in direction of

movement among individuals, but movement rates averaged 0.83 ± 0.50 km/day (0.45 ±

0.27 nmi/day), with a range of 0.08 to 2.53 km/day (0.04 to 1.37 nmi/day), and a prevailing

overall trend of movement to the north and northeast.

CONTENTS

ABSTRACT ............................................................................................................................... iii

INTRODUCTION ..................................................................................................................... 1

METHODS ................................................................................................................................ 6

Survey Design and Pots ....................................................................................................... 6

Oceanographic Sampling ..................................................................................................... 9

Red King Crab Sampling ..................................................................................................... 9

Bycatch Sampling ................................................................................................................ 12

Red King Crab Tagging ....................................................................................................... 12

Graphical and Statistical Analyses....................................................................................... 13

Public Data Repository ........................................................................................................ 14

RESULTS .................................................................................................................................. 14

Survey Completion .............................................................................................................. 14

Oceanographic Conditions ................................................................................................... 15

Red King Crab Catch Composition ..................................................................................... 15

Red King Crab Spatial Distribution ..................................................................................... 17

Other Crab Species .............................................................................................................. 18

Fish and Macroinvertebrates ................................................................................................ 19

Red King Crab Tagging ....................................................................................................... 19

DISCUSSION ............................................................................................................................ 20

ACKNOWLEDGMENTS ......................................................................................................... 25

CITATIONS .............................................................................................................................. 27

TABLES .................................................................................................................................... 36

FIGURES ................................................................................................................................... 38

INTRODUCTION

Red king crab (Paralithodes camtschaticus: hereafter “RKC”) once represented one of the most

lucrative fisheries in the Bering Sea and Gulf of Alaska. Following rapid capitalization, the

Bristol Bay fishery exploded in the late 1970s, supported by a mature male biomass that peaked

at ~130,000 metric tons (t) (Zacher et al. 2024). However, in the early 1980s, Bristol Bay RKC

(BBRKC) productivity collapsed by an order of magnitude, culminating in closure of the

directed fishery in 1983. Fishing resumed the following year, but it exploited a population that

was composed of a considerably lower biomass of both mature-sized males (i.e., ≥ 120 mm

(4.7 in) carapace length (CL)) and reproductively mature females (Fig. 1). Since the population

collapse of the early 1980s, stock abundance has been relatively low and variable, with the

abundance of legally harvestable males (i.e., ≥ 135 mm (5.3 in) CL or ≥ 165 mm (6.5 in)

carapace width (CW)) fluctuating between a low of approximately 5,400 t in 1985 and a high of

~52,000 t in 1991 (Zacher et al. 2024). The 1991 peak had appeared to represent a period of

stock recovery, but the fishery was closed for a second time in 1994 due to declining female

spawning biomass and remained closed in 1995. This second closure period led to the adoption

of a rebuilding plan, supported by the development of a length-based stock assessment model

(Zheng et al. 1995a, 1995b) and a formal management strategy evaluation (Zheng et al. 1997a,

b). A modest increase in RKC abundance followed and continued through the early 2000s.

However, a declining trend in total biomass has been observed in recent years for both mature

males and females, with the decline in the males beginning in approximately 2004 and since at

least 2014 for females (Fig. 1). The 2021 female spawning stock biomass is estimated to have

been at its lowest level since 1995 (Zacher et al. 2024) and the fishery was once again closed for

the 2021/22 fishing season; it remained closed for the 2022/23 season, since estimated mature

female biomass increased by less than 4% relative to 2021 (Zacher et al. 2024). In response to

the consecutive closures of the BBRKC fishery in 2021 and 2022, in September 2022 the Alaska

Bering Sea Crabbers (ABSC), a trade organization representing Bering Sea crab harvesters,

submitted a petition to the North Pacific Fishery Management Council (NPFMC; the “Council”)

requesting short-term emergency action to protect RKC and crab habitat from fisheries-induced

disturbances. Management of commercial fisheries in the Bristol Bay District has a long history

of restrictive measures that have resulted in the establishment of a series of closure areas in

which the activities of various harvest sectors are limited. Four closure areas (Fig. 2) are of

particular relevance to the management of BBRKC:

1) Bycatch Limitation Zone 1 (BLZ1), encompassing Bristol Bay waters north of the

Alaska Peninsula, south of 58° 00’ N lat., and east of 165° 00’ W long.; this is further

divided into Reporting Area 516 spanning 162° 00’ to 163° 00’ W long. and Reporting

Area 509 spanning 163° 00’ to 165° 00’ W long.

2) The Red King Crab Savings Area (RKCSA), spanning 56° 00’ to 57° 00’ N lat. and

162° 00’ to 164° 00’ W long.

3) The Red King Crab Savings Subarea (RKCSS), defined as waters within the RKCSA

between 56° 00’ and 56° 10’ N lat.

4) The Nearshore Bristol Bay Trawl Closure Area (NBBTCA), defined as all Bristol Bay

waters east of 162° W long., within which lies the Northern Bristol Bay Trawl Area

(NBBTA), located to the south and west of the Nushagak Peninsula, spanning 58° 00’ to

58° 43’ N lat. and 159° 00’ to 160° 00’ W long.

BLZ1 was the first of these management areas to be established, via Amendment 10 to the

Bering Sea and Aleutian Islands (BSAI) Groundfish Fishery Management Plan (FMP).

Amendment 10 was first enacted via emergency rule on 3 June 1986 (U.S. Department of

Commerce 1986) and permanently adopted in March of 1987 (U.S. Department of Commerce

1987). The Amendment addressed concerns that bycatch of RKC and Tanner crabs

(Chionoecetes bairdi) by domestic and joint-venture groundfish trawl fisheries was contributing

to low crab abundance. Amendment 10 closed a section of BLZ1 (waters between 160° 00’ W

and 162° 00’ W long. from the Alaska Peninsula in the south to 58° 00’ N lat.) to trawling year-

round. Areas immediately to the east and west within BLZ1 remained open to trawl fisheries but

with bycatch limits for RKC and Tanner crabs established for both domestic and foreign fleets

targeting yellowfin sole (Limanda aspera) and other flatfish. Amendment 12A, enacted in 1989

(U.S. Department of Commerce 1989), established Statistical Area 516 spanning 162° 00’ to

163° 00’ W long. and closed that area to all trawl gear between 15 March and 15 June each year,

with an exception for directed fishing for Pacific cod (Gadus macrocephalus) along the Alaska

Peninsula, south of a line running from northeast to southwest and approximating waters

shallower than 25 fm, subject to a bycatch cap of 12,000 RKC. Between 160° 00’ and

162° 00’ W long., the Amendment allowed the U.S. Secretary of Commerce to authorize trawl

fishing for Pacific cod “provided that such fishing is in compliance with a scientific data

collection and monitoring program, established by the Regional Director after consultation with

the Council”. Currently, Area 516 of BLZ1 is closed to all trawling from 15 March through

15 June (U.S. National Archives and Records Administration 2023).

The RKCSA was first established by emergency interim rule in January 1995, in response to the

RKC fishery closures of 1994-95. It closed the area to all trawl gear from 20 January through

25 April 1995, “to conserve the female red king crab stocks in the Bristol Bay area” (50 CFR

Parts 675 and 677; U.S. Department of Commerce 1995a). That December, the closure was

formalized as an inseason adjustment spanning 20 January through 31 March 1996, with the

stated objective of preventing “an excessive share of red king crab from being taken by the

groundfish trawl fisheries early in the fishing season” (50 CFR Part 675; U.S. Department of

Commerce 1995b). The December action redefined the closure as applying only to “directed

fishing for groundfish by vessels using other than pelagic trawl gear”. In January 1996 the

RKCSA became a permanent year-round closure for non-pelagic trawling (50 CFR Part 679;

U.S. Department of Commerce 1996) and included the establishment of the RKCSS. In

consideration of the area’s importance to rock sole (Lepidopsetta polyxystra) fisheries, the

RKCSS was to “remain open to nonpelagic trawling for groundfish during the years in which a

guideline harvest level for Bristol Bay red king crab is established.” Within this area, a separate

prohibited species catch (PSC) limit was established that was constrained to no more than 35%

of the total PSC apportioned to the rock sole fishery in any given year. The same ruling also

established the Nearshore Bristol Bay Trawl Closure Area (NBBTCA), in which all trawling was

prohibited except within the Northern Bristol Bay Trawl Area (NBBTA): in the NBBTA,

trawling was allowed from 1200 hr on 1 April through 1200 hr on 15 June of each year (U.S.

Department of Commerce 1996). Although not explicitly stated as justification within the ruling,

the decision to allow trawling within the NBBTA appears to have been in response to written

public commentary that suggested that “Support exists for … leaving open the subarea between

58° and 58°43’ N. lat., which is a productive yellowfin sole fishing ground”, and to which NMFS

indicated agreement. ABSC’s 2022 petition requested that the RKCSA and RKCSS be closed to

all fishing gears from 1 January to 30 June 2023, by emergency rule. The NPFMC declined to

enact the proposed rule. However, it passed a motion (i.e., D2 Council Motion BBRKC) at its

October 2022 meeting that encouraged the development of “methods to gather data on

interannual and seasonal distribution of crab, such as additional surveys and tagging studies”.

A prior discussion paper, prepared for the Council’s April 2022 meeting, Cunningham and Cates

(2022) had sought to provide “information on Bristol Bay red king crab molting/mating annual

cycle and how seasonality of this overlap with fisheries” and to provide guidance regarding

“responsive spatial management measures … and how they might be applied to protect BBRKC.”

A subsequent analysis responding directly to the ABSC’s emergency rule request (Cates et al.

2022) identified a lack of objective, quantitative information on RKC distributions that could be

used to guide bycatch avoidance throughout the year. In particular, the most unbiased

information on RKC distributions is obtained from the NMFS trawl survey; however, such data

represent only snapshots of summer distribution. Data obtained from the directed fishery provide

insight into the seasonal redistribution of legal-size males (Zacher et al. 2018); however, these

data fail to represent other demographics (i.e., sex, size, or maturity categories) of interest, such

as female spawning stock and sublegal-size individuals of both sexes. Additional information

regarding seasonal redistribution and migration patterns is needed.

Seasonal migration is a common feature of commercially exploited marine species that reside in

the Bering Sea and Aleutian Islands region, including walleye pollock (Gadus chalcogrammus;

Kotwicki et al. 2005), Pacific cod (Bryan et al. 2021), Pacific halibut (Hippoglossus stenolepis;

Loher 2022), and snow crab (Chionoecetes opilio; Nichol and Somerton 2015). For RKC,

seasonal migration of reproductive females has been documented in southeast Alaska using

acoustic tags (Stone et al. 1992). Analyses of fishery logbook and catch data (Zacher et al. 2018)

have suggested that legal-size male crabs in Bristol Bay are found farther to the south and west

in autumn than during the summer, and/or farther from the Alaska Peninsula. These data also

demonstrate that the relative proportion of legal-size males taken from trawl-exclusion areas

varies interannually, likely as a function of temperature. Sex-specific differences in migratory

behavior may arise from differences in life history between the sexes. For example, egg-bearing

females may be more limited in their abilities to move because they need to remain at

temperatures that allow for successful embryo development. In contrast, males may be able to

redistribute throughout the year in order to find habitat that represents a metabolic thermal

optimum for feeding and growth (sensu Hernández-Sandoval et al. 2018). Regardless of the

drivers that are involved, RKC distribution within Bristol Bay is not likely to be static throughout

the year and summer survey data may be insufficient to provide year-round guidance for

avoidance of RKC bycatch at optimal spatial and temporal resolutions.

In addition to obtaining survey data outside of the summer season, Pop-up Archival Transmitting

(PAT) tags can be a powerful tool for studying the movement and environmental conditions

experienced by animals in cases in which data that span specific periods of time are desired. PAT

tags are electronic tags that contain a sensor package, an automated release mechanism, and

satellite-broadcast capabilities, allowing for environmental data to be collected while attached to

the host animal and recovered via satellite telemetry. Broadcast dates (and, hence, period at

liberty) may be pre-specified, and the tag’s final position is determined by the receiving

satellite’s use of the Doppler shift in the received signal (Keating 1995). This has the advantage

of allowing for determination of final location even if individuals move to areas absent of fishery

effort or where reporting of physical recoveries is reduced (e.g., in Russian waters for animals

tagged in Alaska). Additionally, locations during time at liberty can, under ideal conditions, be

inferred from archived light data (sensu Block et al. 1998, Loher 2022) and may allow for state-

space modelling of movement (Pederson et al. 2018, Nielsen et al. 2019) that cannot be achieved

using conventional mark-recapture data. Satellite-tagging studies of BBRKC were first initiated

in July 2020 to study intra-annual movement patterns and the seasonal use of trawl closure areas.

Initial work focused on summer to fall movement of mature-size males to compare data derived

from the fall directed fishery to tagging. More recently, efforts have focused on elucidating

movement into winter and spring, which are particularly important seasons for red king crab,

encompassing molting, larval release, and mating, as well as being a period of higher bycatch in

trawl fisheries. From 2020 through 2022, 470 satellite tags have been deployed on eastern Bering

Sea red king crab (225 females, 245 males) through collaborate research between NMFS, the

Alaska Department of Fish and Game (ADF&G), and the Bering Sea Fisheries Research

Foundation (BSFRF). However, our understanding of the seasonal distribution of BBRKC males

and females in the winter/spring is still incomplete. Using satellite tags on males and primiparous

(i.e., first-spawning) females is challenging because tag attachment does not allow tags to be

retained through the molt and these crab molt in late winter (~February). Multiparous females

(i.e., individuals that have spawned previously) molt later in the spring and, thus, tags can be left

on these animals for longer periods; however, scaling individual movement vectors to population

level distribution patterns is challenging.

In the current study, a sampling project employing modified commercial king crab pots (traps)

was executed during early spring, 2023, within a portion of the Bristol Bay RKC management

district to: a) evaluate crab distribution in comparison to those observed during summer trawl

surveys; b) investigate maturity, molting, and reproductive status, and; c) tag mature-size male

red king crabs with satellite-transmitting archival tags programmed to detach and report during

the summer of 2023, coincident with the prosecution of the summer trawl survey.

METHODS

Survey Design and Pots

The complete survey design was composed of a total of 694 stations arranged in 11 transects,

each running approximately north-to-south, with transects separated by 15.0 nautical miles (nmi)

(27.7 km) and spanning approximately 159° 39’ to 164° 16’ W long. from east to west (Fig. 3).

Individual stations were positioned 2 nmi (3.7 km) apart along each transect and the transects

extended from shallow waters (i.e., minimum depths of 14 fm (26 m)) in southern Bristol Bay to

approximately 57° 50’ N lat. This design resulted in a grid that covered approximately 35% of

the spatial extent of the BBRKC management District and falling within an area that during the

NMFS EBS Continental Shelf summer trawl survey (Zacher et al. 2024) is represented by 47

trawl stations. Over the last 10 years, this area has contained, on average, 91 ± 1 % of all mature

female and 83 ± 2 % of all mature-sized male RKC that have been captured during NMFS EBS

summer trawl surveys.

Fishing was conducted by two vessels (Fig. 4):

1) FV Silver Spray, a 130-ton (118 t), house-forward crab vessel measuring 116 ft

(35.4 m) in length overall (LOA) and 30 ft (9.1 m) beam; homeport Kodiak, AK.

2) FV Summer Bay, a 196-ton (178 t), house-aft crab vessel measuring 107 ft (32.6 m)

LOA and 26 ft (7.9 m) beam; homeport Dutch Harbor, AK.

At each station that was fished during the pot survey, latitude and longitude of pot-setting was

recorded to the nearest 0.01 ft as determined by the GPS unit on the vessel’s bridge and recorded

at the vessel’s position when the pot first landed in the water. Water depth at the same position,

according to the depth sounder on the bridge, was recorded to the nearest 0.1 fm (~ 0.2 m) and

time set and hauled were recorded, to the nearest minute, as the time that the pot left the pot

launcher until hauling began, defined as the time when line retrieval via the pot hauler was

initiated.

Fishing was conducted using modified square commercial king crab pots. The pots used on both

vessels were constructed of a double frame: an outer frame composed of 1.5 in (38 mm) round

steel rod; and an inner frame, which supported the pot’s webbing, composed of 0.75 in (19 mm)

round steel rod (Fig. 5). On the Silver Spray, the outer frame measured 80.5 in (2.05 m) square

by 33 in (0.84 m) tall and the inner frame was 77.25 in (1.96 m) square by 31 in (0.79 m) tall; on

the Summer Bay, the outer frame measured 84 in (2.1 m) square by 34 (0.86 m) tall and the inner

frame was 78 in (2.0 m) square by 32 in (0.81 m) tall. The double-frame design of these pots

allows for the outer frame to take the landing force and abrasion of the seabed while protecting

the pot’s webbing from damage. All pots contained two rectangular funnels on opposing sides of

the pot. The funnels spanned the entire width and height of the pot wall at their outer opening

and tapered to a rectangular opening inside of the pot. Each funnel was upward-sloping (i.e., the

floor of the funnel was longer than its roof) and the opening was mounted in the funnel’s roof

such that the funnel’s opening pointed largely upwards (Fig. 5, upper). On the Summer Bay, the

funnel openings measured 38 in (96.5 cm) by 11 in (28.0 mm) and extended a maximum distance

of ~28 in (70 cm) into the pot at the lower lip of the opening, which was positioned

approximately 22 in (56 cm) above the floor of the pot (i.e., this is the distance that a crab would

“drop” upon entering an empty pot) (Fig. 5). The funnels of the pots used by the Silver Spray

were of slightly variable specifications: funnel width was 34.5 in (87.6 cm) with heights ranging

from 7.5 in to 9 in (19.0 to 22.0 mm); the funnels extended a maximum distance of 23.25 in

(59.0 cm) into the pot at the lower lip of the funnel’s opening and were positioned between 16 in

and 20 in (40.6 to 50.8 cm) above the floor of the pot. Funnels on the pots used by the Summer

Bay were not fitted with triggers or funnels. Some pots used by the Silver Spray were fitted with

plastic funnel hoods; however, these hoods were propped open (Fig. 5) in order to disable them

and not impede the entry of crabs into the pot (Fig. 5). On pots used aboard the Silver Spray, the

body was lined with 5.25 in (13.3 cm) stretched-mesh webbing and the funnels lined with 3.75 in

(9.5 cm) stretched-mesh webbing. On pots used aboard the Summer Bay, the body was also lined

with 5.25 in (13.3 cm) stretched-mesh webbing and the funnels lined with 3.5 in (8.9 cm)

stretched-mesh webbing. These webbing sizes are smaller than used on red king crab pots during

commercial fishing, which are required to contain at least one panel composed of a minimum of

9 in (22.9 cm) stretched-mesh. Smaller meshes were employed herein to enhance the retention of

sublegal-size and juvenile crabs. Where pots had been constructed with escape rings, these were

covered by webbing and therefore not functional; again, this was to prevent small crabs from

escaping the pots. All pots were equipped with a section of webbing that was secured with

biodegradable cotton twine, which would degrade and allow crabs and other bycatch to escape

from the pots if they were lost on the grounds. Pots weighed between 760 and 810 pounds (345-

367 kg), unbaited.

Each pot was baited using approximately 8 pounds (3.6 kg) of fresh-frozen (i.e., unsalted),

chopped Pacific herring (Clupea pallasii) that was contained within a single 14 in × 18 in (36 cm

× 46 cm) bait bag hung from the center of the pot’s roof (Fig. 5, upper) and introduced into the

pot through a side-panel that also served as the door for emptying the pot of its catch (Fig. 5,

lower). Each pot contained a bridle that was attached to two “shots” (i.e., 33 fm (60 m)) of buoy

line: one shot of sinking (nylon) line was attached to the pot bridle and one shot of floating

(polypropylene) line led from the sinking line to the first pot buoy. Two buoys were employed:

an A3 “diver” buoy (i.e., measuring approximately 17 in (43 cm) in diameter and 23 in (58 cm)

long, including the eye, and containing ~14.5 gal (55 l) of air); followed by a shorter length (~10

fm; 18 m) of floating line that led to an LD2 (11 in (28 cm) by 24 in (61 cm)) trailer buoy. In

addition, the Silver Spray employed a standard 12 in (15 cm) by 6 in (30 cm) cork as a third and

final buoy. When fishing particularly shallow stations, the Silver Spray removed one shot of

buoy line.

Oceanographic Sampling

Oceanographic conditions and depths fished were monitored using dataloggers affixed to the

pots. A combination of three models of datalogger manufactured by RBR Ltd. (Ottawa, Ontario,

Canada; https://rbr-global.com/about-rbr/contact-rbr/) were employed: 1) XR-420-CTD (n = 11);

2) RBRduet TD (n = 6), and; 3) TDR-2050 (n = 4). The XR-420-CTD is a cylindrical unit that

measures 310 mm (12.2 in) in length and 64 mm (2.5 in) in diameter and records temperatures

between -5° and 35° C (23° and 95° F) at a resolution of < 0.00005° C (< 0.00009° F) and

nominal accuracy of ± 0.002° C (0.0036° F); and conductivities (i.e., salinities) from 0 to 85

mS/cm at 0.01 resolution and nominal accuracy of ±0.003 mS/cm at 35 psu and 15° C (59° F).

The RBRduet TD is a cylindrical unit that measures 200 mm (7.9 in) in length and 25.4 mm (1.0

in) in diameter and records temperature at the same resolution as the XR-420-CTD. TDR-2050s

were the manufacturer’s precursor to the RBRduet, measured 235 mm (9.3 in) by 38 mm (15.2

in) and recorded temperature at resolutions equivalent to the RBRduet. The majority of loggers

(n = 19) were equipped with pressure transducers rated to 2,000 decibar (where 1 dbar of

pressure is nearly equivalent to 1 m (3.28 ft) of seawater); each vessel carried a single logger

with a 1,000-dbar transducer. These transducers were capable of determining water depth to a

resolution of < 2 m (< 6.56 ft) at a nominal accuracy of 1 m (3.28 ft); and a resolution of < 1 m

(< 3.28 ft) at a nominal accuracy of 0.5 m (1.64 ft), respectively. All loggers were owned and

administered by ADF&G who routinely return the units to RBR for calibration every three years,

on a rotating basis. For deployment, loggers were placed inside the crab pots, attached to their

roof (Fig. 6), and programmed to record each measured parameter at 10-minute intervals

throughout the pot soak.

Red King Crab Sampling

All RKC that were captured were processed and biological data collected from each crab.

Subsampling protocols were developed in case larger numbers of crabs than could reasonably be

processed were captured at any individual station; however, these protocols did not need to be

employed. The carapace length (CL) of each RKC was measured to the nearest 0.1 mm as the

distance across the crab’s dorsal surface from the center of the posterior margin of the carapace

to the base of one of the eye orbits at the base of the rostrum (Fig. 7, upper). Measurements were

taken using a variety of mechanical and digital calipers (Fig. 7, lower): 1) Mitutoyo Research

and Development (Kirkland, Washington, USA) mechanical Vernier calipers; 2) Sylvac (Fowler

High Precision, Canton, Massachusetts, USA) S Cal Pro digital calipers, and; 3) iGaging (San

Clemente, California, USA) Absolute Origin IP54 0-12 in bluetooth-enabled digital electronic

calipers.

RKC were identified by sex and additional data were collected depending upon the sex of the

individual. Shell condition in female RKC may be an indicator of imminent breeding potential,

as female RKC do not store sperm (i.e., unlike Tanner and snow crabs (Chionoecetes opilio);

Adams and Paul 1983, Saint-Marie and Lovrich 1994) and must therefore mate during each

year’s molting cycle. Shell hardness may affect a crab’s vulnerability to fishing gear and

subsequent probability of survival following return to the sea (sensu Stoner et al. 2008, Yochum

et al. 2017), and shell condition in both sexes is used as an input in stock assessment models as it

may be a predictor of parameters such as molting probability, growth increment, and mortality

rates (Zheng et al. 2021). For all crabs, shell condition was assigned to one of the following

categories, consistent with the descriptions found in Donaldson & Beyersdorfer (2003): 0 =

premolt or molting; 1 = recently-molted, soft and pliable; 2 = new hard-shell, both firm and

clean; 3 = old-shell, slightly worn; 4 = old-shell, worn; 5 = very old-shell. Note that shell

hardening in RKC is a progressive process in which the shell can require in excess of 2 months

post-molt to achieve full harness (Stevens 2009). Evaluation of whether any given shell was

“pliable” during the current survey was determined subjectively; that is, no quantitative measures

of shell “hardness” (e.g., via durometer readings: Stevens 2009) were used to determine the

division between Shell Conditions 1 and 2.

For mature female RKC, a given individual’s reproductive status and position in the molt-mate

cycle can be inferred from an examination of the eggs that she bears. Completion of the molt-

mate cycle is indicated by uneyed (i.e., recently extruded) eggs. Conversely, the presence of eyed

eggs (i.e., containing visible embryos), hatching eggs, or empty egg cases indicate the

progression of egg incubation toward and through larval release; and absence of eggs in

morphologically-mature females (a.k.a. “barren”) may be an indicator of reproductive failure

(e.g., environmentally or physiologically induced (Ganji 2011) skipped spawning (sensu

Jørgensen et al. 2006), or a relative lack of suitable mates (sensu Baker et al. 2022)). For female

RKC, egg clutch assessments were conducted as per NMFS EBS trawl survey protocols (Zacher

et al. 2024). The presence or absence of eggs was noted and the development stage (i.e., egg

“condition”) and the size of each egg clutch was recorded. Egg condition categories were defined

as follows: 0 = no eggs; 1 = uneyed; 2 = eyed; 3 = dead; 4 = empty egg cases; 5 = hatching.

Determination of the presence/absence of “eyes” (i.e., developing embryos) within the eggs was

conducted with the naked eye and did not employ magnifying devices. Clutch size categories

were defined relative to the expected size of a full clutch, where a full clutch is expected to fully

cover the abdomen and causes considerable distension of the abdominal flap due to its mass

(Donaldson and Beyersdorfer 2003). Clutch fullness was assigned to the following categories:

0 = no eggs, crab is immature; 1 = mature crab with no eggs; 2 = trace to 1/8 clutch; 3 = 1/4

clutch; 4 = 1/2 clutch; 5 = 3/4 clutch; 6 = full. Assignment to a clutch fullness category was

subjective (i.e., no empirical volumetric measurements were taken) and each crab was assigned

to the fullness category that came closest to its estimated clutch size (e.g., a female whose clutch

appeared to be 60% full would be assigned category “4” because it is closer to 50% than to

75%). For female RKC that were not egg-bearing, maturity was determined on the basis of

ventral anatomy, according to Donaldson and Beyersdorfer (2014). In mature females, the

abdominal flap entirely covers the first coxa (i.e., basal section) of each of the walking legs,

whereas in immature individuals the abdominal flap is relatively small and the coxae of the

walking legs are exposed.

For male lithodid crabs, morphometric maturity may be inferred from changes in chela (claw)

height relative to carapace length and width (sensu Olsen 2016) and physiological maturity is

indicated by the development and presence of spermatophores (Filina 2011). However, for

regulatory purposes, ADF&G simply defines “mature” as meaning “male red king crab that are

4.7 inches (120 mm) or more in carapace length” (ADF&G 2023). For male RKC, we will

follow that convention to facilitate comparisons between results of the current survey and both

ADF&G and NMFS documents describing similar aspects of the stock. By extension, we will

refer to all male RKC that are < 120 mm (< 4.7 in) CL as “immature-size”, regardless of their

functional abilities to reproduce. Finally, males ≥ 135 mm (5.3 in) CL will be referred to as

“legal-size” males, as this currently represents the minimum size for retention in the directed

fishery.

All RKC were visually inspected for signs of disease and, if noted, the apparent nature of the

disease was recorded. Specifically, crab were scanned for the following pathologies: 1) bacterial

shell disease (Meyers and Burton 2009); 2) rhizocephalan barnacles (esp. Briarosaccus spp.;

Sheilds 2012, Sloan and Hardy 2017); 3) cottage cheese disease (i.e., microsporidian infection;

Stentiford et al. 2014); 4) leatherback (i.e., incomplete calcification of the exoskeleton; Morado

et al. 2014), and; 5) snailfish (Liparidae) eggs (Gardner et al. 2016).

Bycatch Sampling

At each station, all crabs were sorted by species. Hybrid crabs representing a cross between

Tanner and snow crab were identified by a combination of characteristics including curve of the

epistome margin, eye color, carapace shape, and space between or shape of the rostrum horns

(Karinen and Hoopes 1971, Urban et al. 2002). Tanner crabs, snow crabs, and Tanner-snow

hybrids were enumerated by sex. Fish were enumerated by species and non-crab invertebrates

were identified to lowest known taxa.

Red King Crab Tagging

Wildlife Computers (Redmond, Washington, USA) Pop-up Archival Transmitting (PAT) tags

were deployed on 100 mature-size male RKC that had recently molted and were in a new hard-

shell condition. Two models of tag were used: 20 miniPATs; and 80 mrPAT “mark-report” tags.

The miniPAT measures 118 mm (4.64 in) in length by 38 mm (1.50 in) in maximum diameter,

with a plastic-coated braided-cable antenna protruding from the distal end. The miniPAT is

capable of recording temperature, depth, and ambient light levels for periods of up to 2 years at

recording intervals of one minute; or recording at longer or shorter logging intervals depending

upon intended deployment duration. The mrPAT is somewhat smaller, measuring 118 mm (4.64

in) by 28 mm (1.10 in) and records daily minimum and maximum temperature and tag-tilt. Only

crab with no, or very minimal injuries (e.g., spine breaks), were selected for tagging. Crabs that

met the tagging criteria were placed in a tank with flowing seawater as soon as possible upon

capture and there awaited tagging. The minimal tagging criteria required five new hard-shell

mature males to be caught within a 5-pot string of gear. To distribute tags across the entire

survey grid, one tag was deployed every other 5-pot string when the minimal criteria were met.

In addition, more tags were placed at sites that met the hotspot criteria. If a 5-pot string captured

> 100 new hard-shell mature males, five crab were tagged from that string. A total of four

“hotspots” of crab catch were identified. Following completion of all of the standard survey

stations, undeployed tags remained; thus, to increase tagging density at hotspot sites, pots were

reset in hotspot areas, tagging a total of 13 to 15 crab within each hotspot. Tags were attached to

crabs by means of a polyolefin tubing harness that wrapped around the crabs’ carapace, going

around the second walking legs (Fig. 8). The positively buoyant tag floats approximately 7 cm

(2.75 in) above the crab.

Graphical and Statistical Analyses

For NMFS summer trawl survey data, total crab abundance is estimated annually from the raw

survey data using area-swept methods (Zacher et al. 2024) and subsequent quantitative stock

assessment modeling (Palof and Siddeek 2022). Area-swept methods cannot be applied to pot

survey data, and drawing similar inferences based on pot data would require, among other

factors, a refined understanding of the attractive radius and distance-dependent fishing power of

the traps (sensu Aedo and Arancibia 2003) under a variety of underlying environmental

conditions. Quantitative abundance estimation methods based on pot/trap data do exist for a

limited number of crab stocks: management of Florida stone crab (Menippe spp.) has relied on

surplus production modeling based on commercial catch data from the trap fishery (Muller et al.

2006) and assessment models based on pot surveys have been employed for southeast Alaska

RKC (see Quinn II et al. 2006). However, no such models exist for BBRKC and developing

abundance estimation techniques for this stock based on pot survey data would require surveys

that more-fully encompass the geographic range of the stock as well as multiple years of survey

data. Herein, we will make no attempt to estimate the absolute or relative abundance of any

demographic of RKC sampled and will instead simply report results as total numbers of crabs

captured within each sex, size, and maturity category of interest and the ratios of total catch

among those demographics. Raw temperature data were interpolated for the survey area via

ordinary kriging using R statistical software (R v.4.2.2; R Core Team 2023). Where means

(averages) are reported, errors will represent on standard deviation about the mean, unless

otherwise noted.

Public Data Repository

Data generated during the course of this survey have been made publicly available and may be

accessed from NMFS’ Alaska Fisheries Science Center Shellfish Assessment Program’s GitHub

site.

RESULTS

Survey Completion

A total of 637 standard survey stations were fished between 18 March and 4 April 2023; 59

planned stations were not fished due to logistical considerations (e.g., location too shallow) and

time constraints (Fig. 3). One additional station was dropped from the final dataset because the

pot had been left unbaited. Among fished stations, 299 were fished by the FV Summer Bay and

338 by the FV Silver Spray (Fig. 3). Realized station coordinates resulted in a total of 99 stations

within the RKCSA (i.e., 15.7% of stations fished), 24 stations (3.7%) within the RKCSS, and

271 stations (42.5%) within the NBBTCA; all stations were within BLZ1. Station depths ranged

from 14.0 to 50.6 fm (25.6 – 92.5 m). Ideally, soak time at each station would have been

approximately 30 hours; however, logistics associated with weather, processing of catch, and

running time between stations imparted variance around the ideal. Realized soak times ranged

between 27.5 and 79.1 hours with the majority of soak times (92%; n = 586) falling within a

positively-skewed distribution (Fig. 9) that spanned 27.5 – 48.8 hours. Falling to the right of (i.e.,

longer than) the primary distribution of soak times were two additional groupings: one composed

of 20 stations with soak times ranging from 52.8 to 53.1 hours; and a second group composed of

29 stations with soak times of 69.9 – 79.1 hours (Fig. 9).

In addition to the standard survey stations, 47 experimental potlifts were conducted, as follows:

1) 30 potlifts were conducted from 3 to 6 April on survey Transects C, E, and I to collect

additional crabs for tagging; 2) 5 potlifts were conducted between 21 March and 3 April to

compare catch rates using varying volumes (i.e., two and four bait bags) and types of bait (i.e.,

herring and cod) and to observe catches using underwater cameras, and; 3) 12 potlifts conducted

on 5 April for tagging. The results and graphics that follow will not include the additional

stations; they will be limited to the 637 potlifts conducted at standard survey stations.

Oceanographic Conditions

Temperature loggers were deployed at 38.6% (n = 246) of standard stations fished, distributed

fairly evenly across the survey area (Fig. 10, lower). Mean water temperatures (i.e., averaged

over the course of each pot soak when the pots were determined to be on-bottom) at individual

stations ranged from -1.22 to 4.38° C (29.84 – 39.88° F) and averaged 2.02 ± 1.08° C (35.06 ±

1.94° F). The warmest temperatures were observed in the southwest of the survey area, closest to

deepwater habitat north of Unimak Pass, and coldest temperatures were encountered in the

northwest, in relatively shallow habitat southwest of Cape Newenham (Fig. 10, lower). Overall,

bottom temperatures in the surveyed region were cooler than observed during the NMFS EBS

summer trawl surveys that were conducted before and after the pot survey (i.e., during the

summers of 2022 and 2023; Fig. 10, upper). Although sea ice was not encountered at any of the

pot survey stations, relatively dense ice coverage was reported just north of the survey grid

during the survey’s first week and the ice retreated to waters offshore and west of Cape

Newnham, and along the Alaska Peninsula in the Kvichak Bay region, by the time the survey

was completed (Fig. 11). During sampling, the footprint of the associated cold pool extended

into the survey grid in its northwest corner (Fig. 10, lower).

Red King Crab Catch Composition

A total of 10,191 RKC were captured (Table 1) at 450 (70.5%) of the standard survey stations:

76.8% (n = 7,824) of these crabs were male and 33.2% (n = 2,367) were female. Considering

only mature-sized individuals, the observed sex ratio was 72.1% male. This departs substantially

from recent EBS trawl survey results, in which catch throughout the Bristol Bay District was

roughly 52% male in 2022 and 37% male in 2023 (Zacher et al. 2024). Male RKC that were

captured at standard survey stations ranged from 17.6 to 190.2 mm (0.69 – 7.49 in) CL; the size

of one individual was not obtained. Among the measured individuals, 36.1% (n = 2,824) were

immature-size (< 120 mm (4.7 in) CL); 63.9% (n = 4,999) were mature-size (≥ 120 mm (4.7 in)

CL); 44.7% (n = 3,497) were legal-size (≥ 135 mm (5.3 in) CL). No molting males were

observed. Immature males were predominantly (98.8%) new hardshell with a small proportion

(1.1%) of old shell and three individuals with very old shell (Fig. 12). The occurrence of old

shell condition increased with size for males larger than ~125 mm (4.92 in) CL, such that in

mature-size males the proportion of new hard decreased to 57.6%, old shell increased to 38.1%,

and 4.2% of individuals were very old shell. Among legal-size males, the proportion of new hard

and old shell were similar (48.5% vs. 45.8%, respectively) and old shell was 5.7%; these were

similar to the relative proportions reported by Zacher et al. (2024) for the 2023 trawl survey.

Across all sizes, a much smoother progression in the advancement of shell conditions with size

can be seen in the CPS1 data than has been visible in recent trawl survey data (Fig. 12).

Female RKC ranged from 57.0 to 174.6 mm (2.24 – 6.87 in) CL: 81.7% (n = 1,934) of these

individuals were determined to be morphometrically mature. Immature females ranged in size

from 57.0 to 99.9 mm (2.24 – 3.93 in) CL and mature females from 82.1 to 174.6 mm (3.23 –

6.87 in) mm CL (Fig. 13). Only five molting individuals were captured, all of which were

immature. The remainder of immature females (98.9%) were new hardshell. Among

morphometrically mature females, 47.6% were new hard-shell and 52.2% were old shell.

Overall, a substantially larger proportion of females were old shell than observed during recent

summer surveys (Fig. 14), especially at sizes greater than ~ 100 mm (3.84 in) CL. No barren

mature females were encountered: all morphometrically-mature females bore egg clutches. No

clutches contained dead eggs, hatching embryos, or empty egg cases. Clutches were composed of

44.3% and 55.7% uneyed and eyed eggs, respectively. The proportion of females carrying eyed

versus uneyed eggs increased progressively with size, with eyed eggs rarely seen in females < 93

mm (3.66 in) CL while representing the large majority of individuals >115 mm (4.53 in) CL

(Fig. 15). Similarly, clutch fullness followed a clear progression of increasing volume with crab

length (Fig. 16), in which half-clutches were represented by a small proportion of individuals

(3.4%) primarily ranging from 84 to 104 mm (3.31 – 4.09 in) mm CL; females carrying three-

quarter clutches produced a strongly regular distribution across individuals of 82 – 119 mm (3.23

– 4.69 in) CL; and full clutches were carried by the majority of individuals ≥ 110 mm (4.33 in)

CL. Overall, 43.5 % of individuals carried three-quarter egg clutches and 53.0% carried full

clutches.

Red King Crab Spatial Distribution

Overall, RKC were distributed throughout the survey area except in its southwestern corner

(Fig. 17, lower): RKC were largely absent south and west of a line running from roughly

56° 50’ N lat. × 164° 15’ W long. southeastward to 52° 50’ N lat. × 162° 27’ W long. Zero-catch

stations were also common on the southern ends of the transects from the Black Hills eastward,

with the exception of the easternmost transect (Transect K; Fig. 17, lower) that terminated

slightly farther offshore than on Transects E-J. The observation of relatively low overall

abundance in the southwest was similar to that which was observed during the 2022 and 2023

NMFS EBS summer trawl surveys (17, upper).

The distributions of legal-size (Fig. 18, lower) and mature-size (Fig. 19, lower) males were

similar to one another, as well as to the distribution of all RKC. Immature-size males displayed a

somewhat patchier distribution than the larger males, especially within the survey’s western

transects (Fig. 20, lower). However, they still possessed an overall footprint that was similar to

that of the larger males. For females, there was a greater disparity between the distribution of

mature and immature individuals. Mature females (Fig. 21, lower) displayed a broad distribution

that was similar to that of males. Immature females were largely absent from the four western-

most transects as well as the survey’s northeastern extent (Fig. 22, lower). Immature females

were largely concentrated to the northeast of the RKCSA, with one “hotspot” located inside the

NBBTCA and a second just north of the RKCSA boundary.

Across all demographics, the majority of crab were caught within the NBBTCA (Table 1): 66%

of all RKC were captured in the NBBTCA and percentages ranged from 61.7% (legal-sized

males) to 75.8% (mature females) among individual crab demographics. For males, just under

20% of each demographic was encountered in the RKCSA, as well as in the BLZ1 outside of the

RKCSA and NBBTCA. For females, the proportion of crab captured inside the RKCSA was

quite different for mature (17.4%) versus immature (7.6%) crabs. A considerably higher

proportion of immature females (21.5%) was found outside of the RKCSA and to the west of the

NBBTCA boundary than mature females (6.8%). This difference in proportional catch appears to

have been due more to an absence of immature females in the RKCSA than due to an abundance

of immature females in BLZ1 outside of the RKCSA.

For no plotted demographic did the overall spring distribution derived from CPS1 data appear

markedly different than the distribution found during the 2023 NMFS summer trawl survey.

However, for immature crabs of both sexes, the CPS1 distributions appear more similar to the

2023 trawl survey plots than to 2022. For crabs of mature and legal sizes, pot survey

distributions appear somewhat less patchy than suggested by the trawl survey data.

Other Crab Species

In addition to RKC, four distinct species of crabs were captured: Tanner crab, snow crab,

horsehair crab (Erimacrus isenbeckii), and Pacific lyre crab (Hyas lyratus). Additionally, a small

number (n = 4) of Tanner-snow crab hybrids were captured. Tanner crabs were the most

abundant (Table 2), represented by 570 individuals captured at a total of 227 stations; most

(98.1%) of these crabs were male. All snow crab and Tanner-snow hybrids were male and

occurred at considerably lower abundance and at fewer stations than Tanner crabs (Table 2).

Tanner crabs were distributed throughout the survey region, with the greatest concentration in

the western half of the grid in a triangle comprising the deepest water and extending

northwestward, roughly parallel to the 100-m isobath (Fig. 23). Snow crabs (Fig. 24) were found

only in the western half of the survey grid, in a distribution that largely overlapped that of Tanner

crab, but with a smaller total footprint.

Fish and Macroinvertebrates

The most commonly encountered fish species (Table 2) were Pacific cod (n = 1,728 individuals

captured at 510 stations) and yellowfin sole (n = 2,393 individuals from 420 stations). Great

sculpin (Myoxocephalus polyacanthocephalus; n = 78) were captured at 69 stations.

Additionally, small numbers of walleye pollock (Gadus chalcogrammus), Pacific halibut

(Hippoglossus stenolepis), northern rock sole (Lepidopsetta polyxystra), starry flounder

(Platichthys stellatus), Alaska plaice (Pleuronectes quadrituberculatus), Alaska skate (Bathraja

parmifera), unidentified skates (Rajidae), and sunflowers seastars (Pycnopodia helianthoides)

were encountered (Table 2).

Pacific cod were broadly distributed throughout the survey grid (Fig. 25) but displayed

somewhat lower abundance along an east-west axis through the central RKCSA and westward

into BLZ1 than elsewhere. Pacific cod were absent from stations on the northern end of

Transects A-D, where the coldest temperatures were recorded. Yellowfin sole were also broadly

distributed and found at highest abundance in nearshore waters along the Alaska Peninsula and

along, and just outside of, the 50-m isobath in northern Bristol Bay (Fig. 26).

Red King Crab Tagging

Tags deployed during CPS1 had a 91% success rate in providing reliable locations with minimal

error ellipses (Fig. 27). New hard-shell mature male RKC had an average movement rate of 0.83

± 0.50 km/day (0.45 ± 0.27 nmi/day), with a range of 0.08 to 2.53 km/day (0.04 to 1.37 mi/day),

over 57–75 days at liberty. There was a high degree of variability in direction of movement (Fig.

27), but with a prevailing trend of movement to the north and northeast (Fig. 28). Tags released

from crabs and reported their locations, providing information that is coincident with the NMFS

eastern Bering Sea trawl survey in Bristol Bay. Survey results and tagging show the same

general area occupied in Bristol Bay (Fig. 29). Additional analyses of finer-scale patterns in

distribution are underway.

DISCUSSION

The current study was largely successful in demonstrating the feasibility of conducting pot

sampling for BBRKC in early spring, thereby generating data on demographic composition,

relative abundance, and stock distribution at a time of year when data for the population have

generally been unavailable. Additionally, the sampling was explicitly designed and executed to

target and sample RKC, without the need to simultaneously survey a wide range of groundfish

species. As a result, considerably more crabs were encountered and sampled during CPS1 than

during the subsequent EBS trawl survey, including nearly three times as many mature females

within the CPS1 grid than were captured during the trawl survey within the Bristol Bay District.

As such, many important aspects of RKC biology may be better-described by the current data

than most years’ trawl surveys have been able to generate. In general, changes in shell condition,

maturity, and egg production according to crab size occurred in considerably clearer progression

within the CPS1 length-frequency plots. Such data can allow for more thorough analyses and

novel insight into aspects of RKC ecology that are difficult or impossible to obtain from summer

trawl survey data. For example, the length or age at which 50% of individuals within a

population become mature (i.e., L50) and the range of sizes over which individuals in a

population reach maturity are important life history parameters used to manage populations and

evaluate their responses to both fishing pressure (Sharp and Hendry 2009) and environmental

change (e.g., McLeay et al. 2019). Ideally, the data describing the maturation process will follow

a smooth sigmoidal (S-shaped) progression over the maturing sizes, thereby allowing confident

estimation of the maturation curve’s inflection point (= L50); such a form can be seen in the

CPS1 data for female RKC (Fig. 12). Ultimately, multiple years of trawl survey data might be

combined to generate a reasonable fit to a sigmoidal maturation curve. However, it can be

unsatisfying and imprecise to pool data over multiple years and derive a longer-term mean when

populations are subjected to environmental change, such that maturation dynamics may change

within the period described by the data pooling.

In most years, the summer trawl survey occurs when molting and mating have been largely

completed, providing an understanding of the results of the most-recent breeding season but less

insight into active spawning and reproductive dynamics within the breeding season. Inspection

of the CPS1 data suggest that it fell largely in the midst of spawning, when primiparous females

had molted and mated and multiparous females were largely preparing to spawn. The length-

frequency distributions depicting shell (Fig. 14) and egg (Fig. 15) condition contain a clear mode

of small crab that had molted and were in new hard-shell condition bearing clutches of recently

extruded uneyed eggs, while most of the larger females had old shells, eyed eggs, and none had

empty egg cases, indicating that they would likely molt soon. The ability to put survey platforms

on the water early in the year can allow for the collection of data that may improve our

understanding of reproductive dynamics, as well as providing data on changes in distribution on

seasonal scales. At the same time, it is important to recognize that the structure of catches may

vary seasonally and across gear types as a function of changes in selectivity, especially as

influenced by the behavior of the crabs. This can be particularly true for baited gear, as changes

in feeding motivation and individuals’ willingness to interact with sampling gear can be

influenced by a variety of factors including age, sex, physiological condition, and breeding

status. In the current survey, of particular note was a substantially different sex ratio in pot

catches relative to that which is commonly observed during summer trawl surveys. The pot

survey results were biased in favor of males to a much greater degree than trawl survey data and

produced a clear lack of molting and recently molted females despite evidence (i.e., the

progression of shell and egg condition classes) that egg hatch and molting was likely ongoing.

For commercially exploited crustaceans, apparent changes in catchability according to size, sex,

and season have been observed elsewhere when sampled using traps. For example, using both

trammel nets (i.e., a form of benthic gillnet) and traps to survey Mediterranean spiny lobsters

(Palinurus elephas), Goñi et al. (2003) observed clear differences in male and female catch rates

based on season. Female catch was quite similar between sampling gears and remained relatively

constant throughout the year. However, male size structure was represented differently between

traps and nets and the relative proportion of males captured followed a seasonal progression in

which males were highly under-represented during the molting period and displayed greatest

catchability when spawning. In Mediterranean spiny lobster, spawning takes place while both the

males and females are hard-shelled, during the intermolt period a few weeks after female molting

(Yeap et al. 2022). Trap-shyness during molting in this species appears to be sex-specific and

displayed primarily by males. For females, the authors (Goñi et al. 2003) hypothesized that

shelter-seeking behavior and their tendency to be more gregarious might enhance their

catchability year-round. The result of the divergent sex-specific behaviors will thus change the

inferred sex ratio of the population as derived from pot sampling, especially among reproductive

size classes, even though little change is likely to be occurring in the underlying population. In

contrast to spiny lobsters, Brunson et al. (2023) found that pots consistently produced a higher

male sex ratio than trawl sampling for blue crab (Callinectes sapidus) in Chesapeake Bay

estuaries. The male bias was further accentuated in summer and winter relative to spring and

autumn. While the authors were unable to explain the apparently greater affinity of males for

pots overall, they hypothesized that the seasonal variance in sex ratios was related to changes in

female catchability due to breeding behavior: in particular, increased catch rates of females when

they are preparing to molt and breed. Sublegal-size females in a pre-molt status (i.e., “peeler”

crabs) are attracted to mature males. Peeler crabs represent an important target demographic for

the commercial fishery because they are held after capture and allowed to molt into marketable

soft-shells (Huang et al. 2015) and the peeler-crab fishery often “baits” its pots with large mature

males in order to increase female peeler catches (Bishop et al. 1983). In cases in which mature

males enter the traps of their own accord during the spawning season, the result may be a marked

increase in female catchability within those pots and the false perception that the underlying sex

ratio has changed.

In the current survey, the general lack of molting individuals in concert with a much lower

proportion of females than is estimated from trawl-survey data is consistent with female pot

shyness. However, closer inspection suggests the results may reflect pot shyness in both sexes

combined with earlier molting in males. The only molting individuals that were captured were

females, despite having caught more than three times as many males. There is no evidence in the

CPS1 data that molting males were inclined to enter the pots. Rather, if females molt later than

males, which is consistent with RKC mate-guarding behavior (Powell et al. 2002) in which

males must be hard-shell either in advance of the females or well afterwards in order to ensure

their ability to clasp and guard their molting mate, then it is likely that the population was

composed of a much higher proportion of molting females than molting males and the females

were therefore underrepresented in the catch. Regardless of the ultimate mechanism (i.e.,

whether pot shyness is sex-specific or the catches were a result of differential molt timing), a

survey that is biased against females could have consequences in terms of the management

actions that might be suggested using the data derived from it. Although the current survey was

not intended to estimate total abundance of any demographic of the population, one of its

objectives was to investigate the spatial distribution of each demographic outside of the summer

season and produce information that might be adapted for use by trawl fleets to avoid RKC

bycatch during winter-spring fisheries. At its June 2023 meeting, the NPFMC moved to “explore

further action that could be implemented through framework agreements for the pot CV sector

and trawl sectors … to reduce BBRKC mortality … responsive to seasonal spatial distribution of

BBRKC and focus avoidance on more discrete areas of relatively higher female BBRKC

abundance” (NPFMC 2023). In order for such guidance to be effective, the data describing

female distribution must be accurate to the greatest degree possible. If pots under-sample females

in late winter and early spring, potentially due to pot shyness associated with molting and

mating, complications and inaccuracies could arise, with the nature of those inaccuracies being

dependent upon the effect of pot-shyness on inferred distribution patterns. For example, if pot-

shy, molting females are distributed evenly throughout the underlying population, then the effect

of undersampling those individuals may simply be a down-scaling of apparent total abundance,

but the data would still provide an accurate representation of relative distribution and the location

of “hotspots” that bycatch fisheries might avoid. However, if the distribution of pot-shy females

is patchy, then the relative distribution inferred from pot sampling may be different than the true

underlying distribution. In particular, failure to locate and characterize aggregations of molting

females that are likely to be the more vulnerable to handling mortality than hard-shell individuals

(Stevens 1990) could create the possibility of guiding bycatch fisheries into the areas where

those crabs exist, instead of avoiding them, simply due to a lack of informative data regarding

their locations. At present, there is no way to infer from the existing data whether female catches

in the current survey were proportional to their underlying distribution or departed from it, or, if

catches were not fully representative of underlying spatial distribution, to what degree they may

have failed to represent specific size class(es), shell, and clutch conditions. Future sampling

should seek to address this issue by including additional, paired sampling using techniques free

from this specific bias (sensu Hanamseth et al. 2022), thereby allowing for a comparison of the

structure and distribution of catches between or among sampling techniques.

In addition to addressing apparent pot shyness, future sampling should seek to standardize pot

gear among vessels, to the greatest degree practicable, in order to avoid any potential spatial

biases within the survey region. For example, the current survey employed pots that had been

manufactured using slightly different webbing sizes on the pots’ main body and funnels. In all

cases, the webbing sizes were considerably smaller than employed during commercial fishing

operations and so their ability to retain large males and mature females is unlikely to have

differed. However, if one were interested in indexing small, pre-recruit individuals then it is

possible that even small differences in webbing sizes could result in slightly different selectivity,

which could translate into perceived spatial variance in the apparent abundance of the smallest

crabs even if no such variance existed. This could be accentuated if pots of different

configuration are used within discrete spatial “blocks” within a survey, such that the selectivity

differences have discrete spatial footprints. For example, in the current survey, a north-south

difference in the perceived abundance or distribution of small crabs could arise due to one vessel

having fished the northern half of the grid with pots that were of slightly different configuration

than the pots used in the southern half of the grid. Ideally, all pots used for future work should be

standardized to ensure equivalent selectivity and fishing power across all demographics of

potential interest, including standardization of pot size, funnel design, webbing sizes; and bait

type, source, quality, and quantity. In cases in which complete standardization is impractical,

differences in selectivity among pot configurations could be examined (e.g., Zhou and Kruse

1999, Herrmann 2021) and accounted for by conducting paired sampling at individual stations to

quantify any differences and applying selectivity coefficients to survey data post hoc to

standardize the resulting catches (sensu Gibson-Reinemer et al. 2017). However, this can be a

large undertaking necessitating dedicated studies and often cannot be directly introduced into the

design of surveys, themselves. Alternatively, if all pots cannot be standardized to a single strict

configuration, then one might elect to evenly distribute pot configurations among all vessels and

deploy them in either a randomized or orthogonal design that eliminates the potential for

systematic spatial bias in catches.

ACKNOWLEDGMENTS

This project was funded primarily by the Alaska Department of Fish and Game and the National

Marine Fisheries Service, with additional support from the Bering Sea Fisheries Research

Foundation. We thank Captain Bill Prout of the FV Silver Spray and Captain Mike Wilson of the

FV Summer Bay and all their crew whose hard work and expertise made this a safe and

successful survey. Katie Palof (ADF&G), Chris Siddon (ADF&G), Gary Stauffer (BSFRF),

Gordon Kruse (BSFRF), and Madison Heller-Shipley (BSFRF) provided guidance during the

project’s design and planning phases. Allie Conrad (NMFS-AFSC), Connor Cleary (NMFS-

AFSC), and Rachel Alinsunurin (ADF&G) provided assistance in gear preparation. Danielle

Lampe (ADF&G) and Jon Richar (NMFS-AFSC) aided in data processing. In addition to the co-

authors who served aboard the survey vessels (E. Ryznar and L. Zacher, field party chief on

Silver Spray), we acknowledge the dedication of the scientific personnel who made up the 2023

CPS1 “crab crew”: Charlie Heller-Shipley (Natural Resources Consultants / BSFRF), Cory

Lescher (Alaska Bering Sea Crabbers / BSFRF), Vicki Vanek (ADF&G), and Jared Weems

(ADF&G, field party chief on Summer Bay).

CITATIONS

Adams, A. E., and Paul, A. J. 1983. Male parent size, sperm storage and egg production in the

crab Chionoecetes bairdi (Decapoda, Majidae). International Journal of Invertebrate

Reproduction 6(3):181-187. DOI: 10.1080/01651269.1983.10510040

Aedo, G., and Arancibia, H. 2003. Estimating attraction areas and effective fishing areas for

Chilean lemon crab (Cancer porteri) using traps. Fisheries Research 60(2-3):267-272. DOI:

10.1016/S0165-7836(02)00177-7

Alaska Department of Fish and Game (ADF&G). 2023. 2023 – 2024 Statewide King and Tanner

Crab Commercial Fishing Regulations. Alaska Department of Fish and Game, Juneau, USA.

207 p. Available:

https://www.adfg.alaska.gov/static/regulations/fishregulations/pdfs/commercial/cf_king_

tanner_crab_2023_2024.pdf

Baker, K. D., Mullowney, D. R., and Saint-Marie, B. 2022. Large males matter: low sperm

reserves in female snow crab (Chionoecetes opilio) off Newfoundland, Canada. Fisheries

Research 253(2022):106385. DOI: 10.1016/j.fishres.2022.106385

Bishop, J. M., Olmi, E. J. III., Whitaker, J. D., and Yianopoulos, G. M. 1983. Capture of blue

crab peelers in South Carolina: an analysis of techniques. Transactions of the American

Fisheries Society 112:(1):60-70. DOI: 10.1577/1548-8659(1983)112<60:COBCPI>2.0.CO;2

Block, A. B., Dewar, H., Williams, T., Prince, E. D., Farwell, C., and Fudge, D. 1998. Archival

tagging of Atlantic bluefin tuna (Thunnus thynnus thynnus). Marine Technology Society

Journal 32(1):37-46. DOI: 10.1007/978-94-017-1402-0_3

Bryan, D. R., McDermott, S. F., Nielsen, J. K., Fraser, D., and Rand, K. M. 2021. Seasonal

migratory patterns of Pacific cod (Gadus macrocephalus) in the Aleutian Islands. 2021.

Animal Biotelemetry 9:24 (2021). DOI: 10.1186/s40317-021-00250-2

Brunson, J. F., Sitta, K. A., Kendrick, M. R., and Kingsley-Smith, P. R. 2023. Evidence in male

bias in Atlantic blue crab pot-based sampling. bioR

iv (preprint). DOI:

10.1101/2023.05.09.538440v1

Cates, K., Marrinan, S., and Smith, M. 2022. Considering a closure to the Red King Crab

Savings Area for all gear types. Discussion Paper C1 RKC Savings Area December 2022.

North Pacific Fishery Management Council, Anchorage, USA. Available:

https://meetings.npfmc.org/CommentReview/DownloadFile?p=80d47407-c90a-44ca-997a-

fcc8c0b7d5cc.pdf&fileName=C1%20Red%20King%20Crab%20Savings%20Area%20Anal

ysis.pdf

Cunninham, S., and Cates, K. 2022. Bristol Bay red king crab information. North Pacific Fishery

Management Council Discussion Paper D1 BBRKC Info Paper April 2022. North Pacific

Fishery Management Council, Anchorage, USA. Available:

https://meetings.npfmc.org/CommentReview/DownloadFile?p=7608c5c6-d20a-4b3e-a23a-

7fb0754d3f71.pdf&fileName=D1%20BBRKC%20Information%20Paper.pdf

Donaldson, W. E., and Beyersdorfer, S. 2003. Biological field techniques for lithodid crabs.

Alaska Sea Grant College Program AK-SG-05-03, University of Alaska, Anchorage, USA.

76 p.

Donaldson, W. E., and Beyersdorfer, S. 2014. Anatomy of king crabs, p. 73-80. In Stevens, B. G.

King (eds.), King Crabs of the World: Biology and Fishery Management. CRC Press, New

York, USA.

Filina, E. A. 2011. Spermatogenesis and physiological maturity of male red king crab

(Paralithodes camtschaticus Tilesius, 1815) and snow crab (Chionoecetes opilio Fabricius,

1788) in the Barents Sea. Marine Biology Research 7(3):289-296. DOI:

10.1080/17451000.2010.497188

Ganji, P. C. N. 2011. Reproductive regulators in decapod crustacean: an overview. Journal of

Experimental Marine Biology and Ecology 214:3-16. DOI: 10.1242/jeb.047183

Gardner, J. R., Orr, J. W., Stevenson, D. E., Spies, I., and Somerton, D. A. 2016. Reproductive

parasitism between distant phyla: molecular identification of snailfish (Liparidae) egg

masses in the gill cavities of king crabs (Lithodidae). Copeia 104(3):645-657. DOI:

10.1643/C1-15-374

Gibson-Reinemer, D. K., Ickes, B. S., and Chick, J. H. 2017. Development and assessment of a

new method for combining catch per unit effort data from different fish sampling gears:

multigear mean standardization (MGMS). Canadian Journal of Fisheries and Aquatic

Sciences 74(1):8-14. DOI: 10.1139/cjfas-2016-0003

Goñi, R., Quetglas, A., and Reñones, O. 2003. Differential catchability of male and female

European spiny lobster Palinurus elephas (Fabricius, 1787) in traps and trammel nets.

Fisheries Research 65:295–307. DOI: 10.1016/j.fishres.2003.09.021

Hanamseth, R., Johnson, D. D., Schilling, H. T., Suthers, I. M., and Taylor, M. D. 2022.

Evaluation of a novel research trap for surveys of blue swimmer crab populations. Marine

and Freshwater Research 73(6):812-822. DOI: 101071/MF21005

Herrmann, B., Grimaldo, E., Brčić, J., and Cerbule, K. 2021. Modelling the effect of mesh size

and opening angle on size selection and capture pattern in a snow crab (Chionoecetes opilio)

pot fishery. Ocean and Coastal Management 201(2021):105495. DOI:

10.1016/j.ocecoaman.2020.105495

Hernández-Sandoval, P., Díaz-Herrera, F., Díaz-Gaxiola, J. M., Martínez-Valenzuela, C., and

Garía-Guerrero, M. G. 2018. Effect of temperature on growth, survival, thermal behavior,

and critical thermal maximum in the juveniles of Macrobranchium occidentale (Holthius,

1950) (Decapoda: Caridea: Palaemonidae) from Mexico. Journal of Crustacean Biology

3(4):483-488. DOI: 101093/jcbiol/ruy024

Huang, P., Woodward, R. T., Wilberg, M. J., and Tomberlin, D. 2015. Management evaluation

for the Chesapeake Bay blue crab fishery: an integrated bioeconomic approach. North

American Journal of Fisheries Management 35(2):216-228. DOI:

10.101080/02755947.2014.986342

Jørgensen, C., Ernande, B., Fiksen, Ø, and Diechmann, U. 2006. The logic of skipped spawning

in fish. Canadian Journal of Fisheries and Aquatic Sciences 63(1):186-199. DOI:

10.1139/f05-210

Karinen, J., and Hoopes, D. 1971. Occurrence of Tanner crabs (Chionoecetes bairdi) in the

eastern Bering Sea with characteristics intermediate between C. bairdi and C. opilio.

Proceedings of the National Shellfish Association 61:8-9.

Keating, K. A. 1995. Mitigating elevation-induced errors in satellite telemetry locations. Journal

of Wildlife Management 59:801-808. DOI: 10.2307/3801960

Kotwicki, S., Buckley, T. W., Honkalehto, T., and Walters, G. 2005. Variation in the distribution

of walleye pollock (Theragra chalcogramma) with temperature and implications for

seasonal migration. Fishery Bulletin, U.S. 103(4):574-587.

Loher, T. 2022. Dispersal and seasonal movements of Pacific halibut (Hippoglossus stenolepis)

in the eastern Bering Sea and Aleutian Islands, as inferred from satellite-transmitting

archival tags. Animal Biotelemetry 10:18. DOI: 10.1186/s40317-022-00288-w

McLeay, L. J., Doubell, M. J., and Linnane, A. J. 2019. Spatial and temporal variations in female

size at maturity of a southern rock lobster (Jasus edwardsii) population: a likely response to

climate change. PLosOne 14(11):e0225144. DOI: 10.1371/journal.pone.0225144

Meyers, T., and Burton, T. 2009. Diseases of Wild and Cultured Shellfish in Alaska. Alaska

Department of Fish and Game, Fish Pathology Laboratories, Anchorage, USA. 130 p.

Morado, J. F., Shavey, C. A., Ryazanova, T., and White, V. C. 2014. Diseases of king crabs and

other anomalies, p. 139-210. In Stevens, B. G. (ed.), King Crabs of the World: Biology and

Fishery Management. CRC Press, New York, USA.

Muller, R. G., Bert, T. M., and Gerhart, S. D. 2006. The 2006 Stock Assessment Update for the

Stone Crab, Menippe spp., Fishery in Florida. Florida Fish and Wildlife Conservation

Commission, Florida Marine Research Institute, St. Petersburg, USA. Available:

https://sjrda.stuchalk.domains.unf.edu/files/content/sjrda_464.pdf

Nielsen, J. K., Mueter, F. J., Adkinson, M. D., Loher, T., McDermott, S. F., and Seitz, A. C.

2019. Effect of study area bathymetric heterogeneity on parameterization and performance

of a depth-based geolocation model for demersal fishes. Ecological Modeling 24:18-34.

DOI: 10.1016/j.ecolmodel.2019.03.023

Nichol, D. G., and Somerton, D. A. 2015. Seasonal migrations of morphometrically mature male

snow crabs (Chionoecetes opilio) in the eastern Bering Sea in relation to mating dynamics.

Fishery Bulletin, U.S. 113(3):313-326. DOI: 10.7755/FB.113.3.7

North Pacific Fishery Management Council (NPFMC). 2023. C- 4 BBRKC closure area. Council

Motion 1 BBRKC Closure Area, 11 June 2023. North Pacific Fishery Management Council,

Anchorage, USA. Available:

ttps://meetings.npfmc.org/CommentReview/DownloadFile?p=c82d4c84-8e06-4dde-8a14-

c9777cfbde86.pdf&fileName=C4%20Motion%201%20BBRKC%20Closure%20Area.pdf

Olsen, A. P. 2016. Spatial Variability in Size at Maturity and Reproductive Timing of Golden

King Crab (Lithodes aequispinus) in Southeast Alaska. Master’s Thesis. University of

Alaska, Fairbank, USA. 55 p.

Palof, K. J., and Siddeek, M. S. M. 2022. Bristol Bay Red King Crab Stock Assessment in Fall

2022. North Pacific Fishery Management Council, Anchorage, USA. 187 pp. Available:

https://meetings.npfmc.org/CommentReview/DownloadFile?p=b98b90b2-88ab-43c2-9487-

c12cdb4e0a25.pdf&fileName=BBRKC%20SAFE%202022%20Final.pdf

Pederson, M. W., Righton, D., Thygesen, U. H., Andersen, K. H., and Madsen, H. 2018.

Geolocation of North Sea cod (Gadus morhua) using hidden Markov models and

behavioural switching. Canadian Journal of Fisheries and Aquatic Sciences 65(11):2367-

2377. DOI: 10.1139/F08-144

Powell, Pengilly, D., and Blau, S. F.. 2002. Mating pairs of red king crabs (Paralithodes

camtschaticus) in the Kodiak Archipelago, Alaska, 1960-1984. Pp. 225-246 in Paul, A. J.,

Dawe, E. G., Elner, R., Jamieson, G. S., Kruse, G. H., Otto, R. S., Sainte-Marie, B., Shirley,

T. C., and Woodby, D. (eds). Crabs in Cold Water Regions: Biology, Management, and

Economics. Alaska Sea Grant College Program AK-SG-02-01, Anchorage, USA.

Quinn II, T. J., Shirley, T. C., and Koeneman, T. M. 2006. Southeast Alaska red king crab stock

assessment review. Special Publication No. 06-12. Alaska Department of Fish and Game,

Division of Sport Fish, Research and Technical Services, Anchorage, USA. 40 p. Available:

https://www.adfg.alaska.gov/FedAidPDFs/sp06-12.pdf

R Core Team. 2023. R: a language and environment for statistical computing. R Foundation for

Statistical Computing, Vienna, Austria.

Saint-Marie, B., and Lovrich, G. A. 1994. Delivery and storage of sperm at first mating of

female Chionoecetes opilio (Brachyura: Majidae) in relation to size and morphometric

maturity of male parent. Journal of Crustacean Biology 14(3):508-521. DOI:

10.2307/15498997

Sharp, D. M. T., and Hendry, A. P. 2009. Life history changes in commercially exploited fish

stocks: an analysis of trends across studies. Evolutionary Applications 2(3):260-275. DOI:

10.1111/j.1752-4571.2009.00080.x

Sheilds, J. D. 2012. The impact of pathogens on exploited populations of decapod crustaceans.

Journal of Invertebrate Paleontology 110(2012):211-224. DOI: 10.1016/j.jip.2012.03.011

Sloan, L. M., and Hardy, S. M. 2017. Larval biology and environmental tolerances of the king

crab parasite Briarosaccus regalis. Journal of Parasitology 103(1):22-31. DOI: 10.1645/16-

Stentiford. G. D., Bateman, K. S., Feist, S. W., Oyarzún, S., Uribe, J. C., palacios, M., and Stone,

D. M. 2014. Areospora rohanae n.gen. n.sp. (Microsporidia; Areosporiidae n. fam.) elicits

multi-nucleate giant-cell formation in southern king crab (Lithodes santolla). Journal of

Invertebrate Paleontology 118:1-11. DOI: 10.1016/j.jip.2014.02.004

Stevens, B. G. 1990. Survival of king and Tanner crabs captured by commercial sale trawls.

Fishery Bulletin, U.S. 88(4):731-744.

Stevens, B. G. 2009. Hardening of red king crab (Paralithodes camtschaticus) (TILESIUS,

1815) shells after molting. Journal of Crustacean Biology 29(2):157-160. DOI: 10.1651/08-

3039.1

Stone, R. P., O’Clair, C. E., and Shirley, T. C. 1992. Seasonal migration and distribution of

female red king crabs in a southeast Alaskan estuary. Journal of Crustacean Biology

12(4):546-560. DOI: 10.1163/193724092X00030

Stoner, A. W., Rose, C. S., Munk, J. E., Hammond, C. F., and Davis, M. W. 2008. An

assessment of discard mortality for two Alaska crab species, Tanner crab (Chionoecetes

bairdi) and snow crab (Chionoecetes opilio), based on reflex impairment. Fishery Bulletin,

U.S. 106(4):337-347.

Urban, D., Pengilly, D., Jadamee, L., and Beyersdorfer, S. 2002. Testing carapace morphology

characteristics for the field identification of Chionoecetes hybrids. Pp. 97-113 in Paul, A. J.,

Dawe, E. G., Elner, R., Jamieson, G. S., Kruse, G. H., Otto, R. S., Sainte-Marie, B., Shirley,

T. C., and Woodby, D. (eds). Crabs in Cold Water Regions: Biology, Management, and

Economics. Alaska Sea Grant College Program AK-SG-02-01, Anchorage, USA.

U.S. Department of Commerce. 1986. Foreign Fishing; Groundfish of the Bering Sea and

Aleutian Islands. Federal Register 51(204):37407-37412. Available:

https://www.govinfo.gov/content/pkg/FR-1986-10-22/pdf/FR-1986-10-22.pdf

U.S. Department of Commerce. 1987. Groundfish of the Bering Sea and Aleutian Islands.

Federal Register 52(53):8592-8602. Available:

https://archives.federalregister.gov/issue_slice/1987/3/19/8590-8604.pdf#page=3

U.S. Department of Commerce. 1989. Foreign fishing; Groundfish of the Bering Sea and

Aleutian Islands. Federal Register 54(152):32642-32652. Available:

https://www.govinfo.gov/content/pkg/FR-1989-08-09/pdf/FR-1989-08-09.pdf

U.S. Department of Commerce. 1995a. Groundfish of the Bering Sea and Aleutian Islands Area,

North Pacific Fisheries Research Plan; trawl closure to protect red king crab. Federal

25/pdf/95-1777.pdf

U.S. Department of Commerce. 1995b. Groundfish of the Bering Sea and Aleutian Islands Area,

trawl closure to protect red king crab. Federal Register 60(237):63451-63453. Available:

https://www.govinfo.gov/content/pkg/FR-1995-12-11/pdf/95-30011.pdf

U.S. Department of Commerce. 1996. Fisheries of the Exclusive Economic Zone off Alaska;

groundfish of the Bering Sea and Aleutian Islands Area; trawl closure to protect red king

crab. Federal Register 61(242):65985-65989. Available:

https://www.govinfo.gov/content/pkg/FR-1996-12-16/pdf/96-31850.pdf

U.S. National Archives and Records Administration. 2023. Code of Federal Regulations, Title

50, Chapter VI, Part 679, Subpart B, § 679.22 Closures. Available:

https://www.ecfr.gov/current/title-50/chapter-VI/part-679/subpart-B/section-679.22

Yeap, A. L. K., de Souza Valente, C., Hartnett, F., Conneely, E-A., Bolton-Warburg, M., Davies,

S. J., Johnson, M. P., and Wan, A. H. L. 2022. Barriers in European spiny lobster (Palinurus

elephas) aquaculture: what we know so far? Reviews in Aquaculture 14(4):2099-2121. DOI:

10.1111/rag/12693

Yochum, N., Stoner, A. W., Sampson, D. B., and Rose, C. 2017. A comparison of laboratory-

holding and tag-return methods for evaluating delayed mortality of Dungeness crab (Cancer

magister) discarded in Oregon fisheries. Fishery Bulletin, U.S. 116:126-141. DOI:

10.7755/FB.116.1.2

Zacher, L. S., Kruse, G. H., and Hardy, S. M. 2018. Autumn distribution of Bristol Bay red king

crab using fishery logbooks. PLosOne 13(7):e0201190. DOI: 10.1371/journal.pone.0201190

Zacher, L. S., Richar, J. I., Fedewa, E. J., Ryznar, E. R., and Litzow, M. A. 2024. The 2023

eastern Bering Sea continental shelf trawl surveys: Results for commercial crab species.

U.S. Department of Commerce, NOAA Technical Memorandum NMFS-AFSC-482, 264 p.

Zheng, J., Murphy, M. C., and Kruse, G. H. 1995a. A length-based population model and stock-

recruitment relationships for red king crab, Paralithodes camtschaticus, in Bristol Bay,

Alaska. Canadian Journal of Fisheries and Aquatic Sciences 52:1229-1246. DOI:

10.1139/f95-120

Zheng, J., Murphy, M. C., and Kruse, G. H. 1995b. An update of the length-based population

model and stock-recruitment relationships for red king crab in Bristol Bay, Alaska. Alaska

Fisheries Research Bulletin 2:114-124. DOI: 10.1139/f95-120

Zheng, J., Murphy, M. C., and Kruse, G. H. 1997a. Alternative rebuilding strategies for the red

king crab Paralithodes camtschaticus fishery in Bristol Bay, Alaska. Journal of Shellfish

Research 16:205-217.

Zheng, J., Murphy, M. C., and Kruse, G. H. 1997b. Analysis of the harvest strategies for red king

crab, Paralithodes camtschaticus, in Bristol Bay, Alaska. Canadian Journal of Fisheries and

Aquatic Sciences 52:1229-1246. DOI: 10.1139/f95-120. Alaska Fishery Research Bulletin

54:1121-1134. DOI: 10.1139/cjfas-54-5-1121

Zheng, J., Siddeek, M. S. M., and Palof, K. J. 2021. Bristol Bay Red King Crab Stock

Assessment in Fall 2021. Discussion Paper C1 BBRKC SAFE October 2021. North Pacific

Fishery Management Council, Anchorage, USA. Available:

https://meetings.npfmc.org/CommentReview/DownloadFile?p=3ada484b-7d8c-42f0-9360-

abc1560aa669.pdf&fileName=2%20Bristol%20Bay%20Red%20King%20Crab%20SAFE.

pdf

Zhou, S., and Kruse, G. 1999. Capture efficiency and size selectivity of two types of pots for red

king crabs in the Bering Sea. Alaska Fishery Research Bulletin 6(2):94-103.

Table 1. -- Number of red king crab (Paralithodes camtschaticus) captured at standard survey

stations during the 2023 Bristol Bay Collaborative Pot Sampling (CPS1) survey, and

the proportion of each demographic (i.e., sex, size, or maturity category) that was

captured, within each of four trawl management areas in Bristol Bay, Alaska. For

males, mature-sized versus immature-sized simply represents a size distinction (i.e.,

based on carapace length) that follows regulatory convention, irrespective of any

individual crab’s actual reproductive status. In inches, the cutoff for legal-size is

5.3 in and for mature-size is 4.7 in. For females, maturity indicates morphometric

maturity (i.e., ability to spawn). Trawl management areas are abbreviated as follows:

NBBTCA = Nearshore Bristol Bay Trawl Closure Area; RKCSA = Red King Crab

Savings Area; RKCSS = Red King Crab Savings Subarea; BLZ1-W = waters of

Bycatch Limitation Zone 1 west of 164° 00’ W longitude and not included within the

RKCSA. See Figure 2 for the boundaries of each area. Note that the RKCSS is

subdivision within the RKCSA; therefore, the Total listed for each demographic is

smaller than the sum of catches across all areas; that is, the Total will exclude the

catch listed for the RKCSS.

NBBTCA

RKCSA

RKCSS

BLZ1-W

Demographic

Total

Legal-size (≥ 135 mm) males

3,498

2,160

61.7

689

19.7

1.9

649

18.6

Sublegal-size (< 135 mm) males

4,326

2,796

64.6

804

18.6

308

7.1

726

16.8

Mature-size (≥ 120 mm) males

5,000

3,098

62.0

979

19.6

122

2.4

923

18.5

Immature-size (< 120 mm) males

2,824

1,858

65.8

514

18.2

252

8.9

452

16.0

Mature females

1,934

1,466

75.8

336

17.4

3.8

132

6.8

Immature females

433

307

70.9

7.6

2.1

21.5

Total catch

10,191

6,729

66.0

1,862

18.3

457

4.5

1,600

15.7

Table 2. -- Summary of bycatch species (i.e., excluding red king crab, Paralithodes

camtschaticus) encountered at standard survey stations during the 2023 Bristol Bay

Collaborative Pot Sampling (CPS1) survey in Bristol Bay, Alaska, including the total

number of individuals of each species/sex that were captured and the number of

standard stations at which they were encountered.

Species name

Common name

# captured

# stations

Chionoecetes bairdi

male

Tanner crab

559

223

female

Tanner crab

Chionoecetes opilio

male

Snow crab

female

Snow crab

C. bairdi x opilio

male

Hybrid Tanner-snow crab

female

Hybrid Tanner-snow crab

Erimacrus isenbeckii

Horsehair crab

Hyas lyratus

Pacific lyre crab

Gadus chalcogrammus

Walleye pollock

Gadus macrocephalus

Pacific cod

1,728

510

Hippoglossus stenolepis

Pacific halibut

Lepidopsetta polyxystra

Northern rock sole

Limanda aspera

Yellowfin sole

2,393

420

Platichthys stellatus

Starry flounder

Myoxocephalus polyacanthocephalus

Great sculpin

Pleuronectes quadrituberculatus

Alaska plaice

Bathraja parmifera

Alaska skate

Rajidae spp.

Unidentified skates

Pycnopodia helianthoides

Sunflower seastar

Figure 1. -- Estimated abundance of mature-sized (≥ 120 mm (4.7 in) carapace length) and

morphometrically-mature female red king crab (Paralithodes camtschaticus) in

Bristol Bay, Alaska, from 1979 through 2023, derived from National Marine

Fisheries Service eastern Bering Sea summer trawl survey data.

Figure 2. -- Trawl closure and management areas in Bristol Bay, Alaska. The large area outlined

in black is the extent of the Bristol Bay red king crab (Paralithodes camtschaticus)

management unit; the area outlined in green indicates the intended coverage of the

Bristol Bay Collaborative Pot Sampling (CPS1) survey, conducted in March-April

2023.

Figure 3. -- Design and execution of stations included in the 2023 Bristol Bay (Alaska)

Collaborative Pot Sampling (CPS1) survey. The complete standard design included

all 694 stations depicted. Stations denoted in white were not fished due to logistical

and time constraints, and one station was omitted because the pot had not been

baited, resulting in a total of 637 stations fished. Stations fished by each vessel are

indicated in blue (fished by the FV Silver Spray) and yellow (FV Summer Bay).

Figure 4. -- Vessels that conducted pot fishing for red king crab (Paralithodes camtschaticus)

during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey.

Upper panel: FV Silver Spray. Lower panel: FV Summer Bay (photo credit: Cory

Lescher, Alaska Bering Sea Crabbers).

Figure 5. -- Pots used aboard the FV Silver Spray for capturing red king crab (Paralithodes

camtschaticus) during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling

(CPS1) survey. Pots were modified commercial traps fitted with smaller mesh and

meshed-over escape rings to enhance retention of juvenile and sublegal crab. Upper

panel: Side view of a pot (photo credit: Vicki Vanek, ADF&G). Note the upward-

sloping funnels and centrally-hung bait bag. Lower panel: A pot being emptied of its

catch (photo credit: Cory Lescher, Alaska Bering Sea Crabbers). Note the double-

frame construction of the pots. The black plastic hoods attached to the funnel-ends

have been propped open to become disabled; the rectangles inward of the open

hoods are the openings of the funnels into the pot. An open hood can also be seen on

the left-hand funnel in the upper image.

Figure 6. -- An RBR Ltd. XR-420 CTD datalogger affixed to the roof of a crab-survey pot used

to capture red king crab (Paralithodes camtschaticus) during the 2023 Bristol Bay

(Alaska) Collaborative Pot Sampling (CPS1) survey (photo credit: Vicki Vanek,

ADF&G). CTD = Conductivity (i.e., an indicator of salinity), Temperature, and

Depth meter.

Figure 7. -- Measurement of carapace length (CL) in red king crab (Paralithodes camtschaticus).

Upper: CL is the distance from the center of the posterior margin of the crab’s

carapace, measured from between the marginal spines, to the deepest point of one of

the crab’s eye orbits, at the base of the rostrum. Lower: a crab being measured using

digital calipers (photo credit: Cory Lescher, Alaska Bering Sea Crabbers). Note the

placement of the calipers in the crab’s right eye orbit (the left orbit is visible on the

near side of the rostrum).

Figure 8. -- A Bristol Bay red king crab (Paralithodes camtchaticus) tagged with a Wildlife

Computers (Redmond, Washington, USA) Pop-up Archival Transmitting (PAT)

during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey

(photo credit: Cory Lescher, Alaska Bering Sea Crabbers). The tag is attached to a

polyolefin tubing harness that wraps around the crab’s carapace.

Figure 9. -- Distribution of soak times employed during the 2023 Bristol Bay (Alaska)

Collaborative Pot Sampling (CPS1) survey, targeting red king crab (Paralithodes

camtschaticus).

Figure 10. --Bottom temperature in the CPS1 area. Top panels: Summer temperatures from the

NMFS survey. Bottom panel: March/April temperature from CPS1, with logger

locations.

Figure 11. --Sea ice conditions in Bristol Bay (Alaska) during the course of the 2023 Bristol Bay

(Alaska) Collaborative Pot Sampling (CPS1) survey. Ice cover ranges in density

from red (nearly complete coverage) to light blue (open water with < 10% ice). Sea

ice was not encountered at any of the survey stations but occurred just north of the

survey grid at the initiation of sampling.

Figure 12. --Lower panel: size frequency (by carapace length) distribution of all male red king

crab (Paralithodes camtschaticus) captured during the 2023 Bristol Bay (Alaska)

Collaborative Pot Sampling (CPS1) survey, depicting the abundance of individuals

within 1 mm size bins possessing various shell conditions. Upper panels: male shell

conditions, by length, as observed during U.S. National Marine Fisheries Service

trawl survey data within the Bristol Bay District during the summers of 2022 and

2023.

Figure 13. -- Lower panel: size frequency (by carapace length) distribution of all female red

king crab (Paralithodes camtschaticus) captured during the 2023 Bristol Bay

(Alaska) Collaborative Pot Sampling (CPS1) survey, depicting the abundance

within 1 mm size bins of morphometrically mature and immature individuals.

Upper panels: female maturity, by length, as observed during U.S. National

Marine Fisheries Service trawl survey data within the Bristol Bay District during

the summers of 2022 and 2023.

Figure 14. -- Lower panel: size frequency (by carapace length) distribution of

morphometrically-mature female red king crab (Paralithodes camtschaticus)

captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1)

survey, depicting the abundance of individuals within 1 mm size bins possessing

various shell conditions. Upper panels: mature female shell conditions, by length,

as observed during U.S. National Marine Fisheries Service trawl survey data

within the Bristol Bay District during the summers of 2022 and 2023.

Figure 15. -- Lower panel: size frequency (by carapace length) distribution of morphometrically

mature female red king crab (Paralithodes camtschaticus) captured bins during the

2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey, depicting

the abundance of individuals within 1 mm size bins exhibiting each measure of egg

condition. Upper panels: mature female egg conditions, by length, as observed

during U.S. National Marine Fisheries Service trawl survey data within the Bristol

Bay District during the summers of 2022 and 2023.

Figure 16. -- Lower panel: size frequency (by carapace length) distribution of morphometrically

mature female red king crab (Paralithodes camtschaticus) captured during the

2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey, depicting

the abundance of individuals within 1 mm size bins displaying each measure of

clutch fullness condition. Upper panels: mature female egg conditions, by length,

as observed during U.S. National Marine Fisheries Service trawl survey data

within the Bristol Bay District during the summers of 2022 and 2023.

Figure 17. --Spatial distribution and relative abundance of all red king crab (Paralithodes

camtschaticus) captured during the 2023 Bristol Bay (Alaska) Collaborative Pot

Sampling (CPS1) survey. Spot size is proportional to the number of crabs captured

at each location, as indicated in the legend.

Figure 18. -- Lower panel: Spatial distribution and relative abundance of male red king crab

(Paralithodes camtschaticus) ≥ 135 mm (5.3 in) carapace length (i.e., legal-size)

captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1)

survey. Spot size is proportional to the number of crabs captured at each location,

as indicated in the legend. Abundance data are overlain on smoothed bottom

temperatures obtained from temperature loggers placed inside the pots. Upper

panels: legal-size male red king crab abundance and bottom temperatures observed

during U.S. National Marine Fisheries Service trawl survey data within the Bristol

Bay District during the summers of 2022 and 2023.

Figure 19. -- Lower panel: Spatial distribution and relative abundance of male red king crab

(Paralithodes camtschaticus) ≥120 mm (4.7 in) carapace length (i.e., mature-size)

captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1)

survey. Spot size is proportional to the number of crabs captured at each location,

as indicated in the legend. Abundance data are overlain on smoothed bottom

temperatures obtained from temperature loggers placed inside the pots. Upper

panels: mature-size male red king crab abundance and bottom temperatures

observed during U.S. National Marine Fisheries Service trawl survey data within

the Bristol Bay District during the summers of 2022 and 2023.

Figure 20. -- Lower panel: Spatial distribution and relative abundance of male red king crab

(Paralithodes camtschaticus) < 120 mm (4.7 in) carapace length (i.e., immature-

size) captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling

(CPS1) survey. Spot size is proportional to the number of crabs captured at each

location, as indicated in the legend. Abundance data are overlain on smoothed

bottom temperatures obtained from temperature loggers placed inside the pots.

Upper panels: immature-size male red king crab abundance and bottom

temperatures observed during U.S. National Marine Fisheries Service trawl survey

data within the Bristol Bay District during the summers of 2022 and 2023.

Figure 21. -- Lower panel: Spatial distribution and relative abundance of morphometrically

mature female red king crab (Paralithodes camtschaticus) captured during the

2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey. Spot size is

proportional to the number of crabs captured at each location, as indicated in the

legend. Abundance data are overlain on smoothed bottom temperatures obtained

from temperature loggers placed inside the pots. Upper panels: mature female red

king crab abundance and bottom temperatures observed during U.S. National

Marine Fisheries Service trawl survey data within the Bristol Bay District during

the summers of 2022 and 2023.

Figure 22. -- Lower panel: Spatial distribution and relative abundance of morphometrically

immature female red king crab (Paralithodes camtschaticus) captured during the

2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey. Spot size is

proportional to the number of crabs captured at each location, as indicated in the

legend. Abundance data are overlain on smoothed bottom temperatures obtained

from temperature loggers placed inside the pots. Upper panels: immature female

red king crab abundance and bottom temperatures observed during U.S. National

Marine Fisheries Service trawl survey data within the Bristol Bay District during

the summers of 2022 and 2023.

Figure 23. --Spatial distribution and relative abundance of all Tanner crab (Chionoecetes bairdi)

captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1)

survey. Spot size is proportional to the number of crabs captured at each location, as

indicated in the legend. Abundance data are overlain on smoothed bottom

temperatures obtained from temperature loggers placed inside the pots.

Figure 24. --Spatial distribution and relative abundance of all snow crab (Chionoecetes opilio)

captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1)

survey. Spot size is proportional to the number of crabs captured at each location, as

indicated in the legend. Abundance data are overlain on smoothed bottom

temperatures obtained from temperature loggers placed inside the pots.

Figure 25. --Spatial distribution and relative abundance of all Pacific cod (Gadus

macrocephalus) captured during the 2023 Bristol Bay (Alaska) Collaborative Pot

Sampling (CPS1) survey. Spot size is proportional to the number of fish captured at

each location, as indicated in the legend. Abundance data are overlain on smoothed

bottom temperatures obtained from temperature loggers placed inside the pots.

Figure 26. --Spatial distribution and relative abundance of all yellowfin sole (Limanda aspera)

captured during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1)

survey. Spot size is proportional to the number of fish captured at each location, as

indicated in the legend. Abundance data are overlain on smoothed bottom

temperatures obtained from temperature loggers placed inside the pots.

Figure 27. --Movement vectors for new hard-shell, mature-size male Bristol Bay red king crab

(Paralithodes camtschaticus) that were tagged with Pop-up Archival Transmitting

(PAT) tags in late March to early April 2023, during the 2023 Bristol Bay (Alaska)

Collaborative Pot Sampling (CPS1) survey, and released from crab and reported

locations via satellite from 1 to 3 June 2023.

Figure 28. -- Rose plot showing movement rate and direction of movement between tagging and

tag reporting for new hard-shell, mature-size male Bristol Bay red king crab

(Paralithodes camtschaticus) that were tagged with Pop-up Archival Transmitting

(PAT) tags in late March to early April 2023, during the 2023 Bristol Bay (Alaska)

Collaborative Pot Sampling (CPS1) survey, and whose tags released and reported

final locations via satellite from 1 to 3 June 2023.

Figure 29. --Pop-up locations for pop-up archival transmitting (PAT) tags that were placed on

new hard-shell mature Bristol Bay red king crab (Paralithodes camtschaticus)

during the 2023 Bristol Bay (Alaska) Collaborative Pot Sampling (CPS1) survey.

Tags surfaced while the NMFS eastern Bering Sea trawl survey was surveying

Bristol Bay. Pop-up locations are overlaid on trawl survey results for new hard-shell

mature-size males.

U.S. Secretary of Commerce

Gina M. Raimondo

Under Secretary of Commerce for

Oceans and Atmosphere

Dr. Richard W. Spinrad

Assistant Administrator, National Marine

Fisheries Service.

Janet Coit

April 2024

www.nmfs.noaa.gov

OFFICIAL BUSINESS

National Marine

Fisheries Service

Alaska Fisheries Science Center

7600 Sand Point Way N.E.

Seattle, WA 98115-6349