Resource Assessment & Conservation Engineering Division

Eastern Bering Sea Crab-Groundfish Survey

The Bering Sea Resource Assessment group conducted the annual Eastern Bering Sea Crab-Groundfish Survey from 29 May to 19 July 2001.  Surveys started earlier in the season for the 1999 and 2000 surveys resulted in having to resurvey portions of the area for red king crab (Paralithodes camchaticus) due to the lack of new eggs.  This year, thanks to cooperation with the charter vessels, we were able to conduct gear experiments before the survey rather than after, and start the survey nearer the historic time of 1 June.  As a result, red king crab egg condition was also near normal, and no resurvey was necessary.

This year marked the twentieth survey of the standard time series in which the same gear (83-112 trawl) and the same sampling direction (inner Bristol Bay to the shelf edge) has been followed.  The series consists of 355 planned stations covering 463,000 km² (Figure 1).  We also marked the fifteenth year of completing an additional 20 stations in the northwest corner of the survey to expand the coverage of snow crab (Chionoecetes opilio).

In response to a request from the crab industry we also surveyed another 25 stations during 2001 in the same general area north of the standard survey area.  The need to continue that series will be evaluated.  As part of an effort to improve our estimates of yellowfin sole (Limanda aspera), we surveyed 19 inshore stations beyond the borders of our regular survey surrounding Bristol Bay.  This is the third year in evaluating that experiment.

Despite the unusual winter of 2001 where no sea ice extended into the southeastern Bering Sea, the summer bottom temperatures were near the long-term mean (2001 mean bottom temperature=2.57ºC, long-term mean=2.43ºC). In general, bottom temperatures were colder than average inshore and along the outer shelf, while the middle regime between the 50-m and 100-m isobaths was warmer than average.

The only major species to show a reduction in biomass from the 2000 survey was walleye pollock (Theragra chalcogramma). This decrease had been predicted from the stock assessment models run in 2000.  The bottom trawl estimate was 4.1 million metric tons (t).  There was no midwater-acoustic survey in summer 2001 to evaluate the off-bottom component of the pollock stock.  However, the size composition suggests that incoming year classes may provide improvement in the near term (Figure 2).

Pacific cod (Gadus macrocephalus) size composition results also indicate improvement in coming years to go with the significant increase in biomass in 2001 (Figure 3).  The 2001 estimate of abundance is 830,000 t.  These results are particularly welcome after seeing steady declines in cod since 1994.

Other important species showing increases in 2001 include: Alaska plaice (Pleuronectes quadri-tuberculatus) 538,000 t; Atheresthes sp. 409,000 t; Hippoglossoides sp., 514,000 t; yellowfin sole 1,855,000 t; and northern rock sole (Lepidopsetta polyxystra) 2,415,000 t.

By Gary Walters.


West Coast Team Completes Triennial Bottom Trawl Survey of Groundfish Resources

The West Coast Groundfish team completed the 2001 triennial West Coast bottom trawl survey of groundfish resources between 1 June  and 27 August.  Two fishing vessels, Sea Storm and Frosti, were each chartered for 65 days to conduct the survey.  The survey continues the triennial time series begun in 1977.  This year’s survey exactly replicated those done in 1995 and 1998, which  sampled the same stations each year between 50- and 500-m depth and between Point Conception, California (lat.34º30’N), and mid-Vancouver Island, British Columbia (lat.49º40’N).  Constraints on RACE Division survey resources this year reduced the number of vessel days to 130 from 140 days used in 1998 and 160 days in 1995.  Despite the reduction, we were able to sample all but the northernmost 30-40 miles of the survey area.

A total of 539 trawl hauls were attempted during the survey.  The performance of all of these hauls are currently being evaluated to determine whether the catches accurately represent the abundance and distribution of the groundfish and invertebrates caught.  Catches were sorted by species, weighed, and counted.  Biological information (length, sex, individual weight, maturity, age structures, etc.) was collected from samples of commercially and ecologically important species.  These data are currently being edited and will be added to the RACE Division database of trawl survey results.  After they are analyzed, results will be provided to scientific teams assessing West Coast stocks.

The West Coast Team is indebted to the many scientists from the AFSC, the Northwest Fisheries Science Center, and other institutions, as well as to the captains and crews of the vessels, all of whom contributed to make this survey  a success.

By Mark Wilkins.


2001 Gulf of Alaska Biennial Groundfish Assessment Survey

The second in the series of biennial bottom trawl surveys of Gulf of Alaska (GOA) groundfish resources was conducted from 17 May through 25 July 2001. Unlike the 1999 survey, which sampled the continental shelf and slope of the GOA from Islands of Four Mountains in the eastern Aleutian Islands to Dixon Entrance in the eastern GOA, sampling during the 2001 survey was restricted to the continental shelf of the central and western GOA.

Prior to the 1999 survey, groundfish resources in the GOA had been surveyed by the RACE Division on a triennial schedule conducted in 1984, 1987, 1990, 1993, and 1996.  The triennial surveys covered the continental shelf of the GOA in each of the five previous surveys but only included the continental slope in 1984 and 1987 and again in 1999.  It is anticipated that the 2003 survey will again resume sampling the entire GOA continental shelf and slope.

ITINERARY
Survey sampling was conducted aboard the chartered commercial trawlers Vesteraalen and Morning Star.  The 75-day survey period  was divided into four legs of 18-19 days each.  Sampling operations began near the Islands of Four Mountains (long.170ºW) and extended eastward on the continental shelf to the eastern boundary of the central GOA off Prince William Sound (long.147ºW).  Sampling occurred at preselected stations, or nearby alternate stations, in depths ranging from 20 m to 448 m.

OBJECTIVES
The primary focus of the biennial groundfish surveys is to build a standardized time series of data designed to assess, describe, and monitor the distribution, abundance, and biological condition of various GOA groundfish stocks.  Specific objectives of the 2001 survey were to:

1. Define the distribution and relative abundance of the principal groundfish and invertebrate species inhabiting the GOA.
     
2. Collect data to define various species-specific biological    parameters, such as age, sex, size, growth rates, length-weight relationships, and feeding habits.
     
3. Collect integrated net configuration and position data for all trawl hauls to obtain precise area-swept estimates.
     
4. Record surface-to- bottom water column temperatures.
     
5. Perform special collections as requested by cooperating research groups.
   

RESULTS
Sampling proceeded from west to east.  Each survey vessel was allocated an equal number of randomly selected stations from each stratum.  Some pre-assigned stations were not sampled due to unsuitable bottom conditions.  In cases where trawlable bottom could not be found at a given station, a preselected alternate location was sampled.  Of the 528 attempted standard survey tows, 489 tows were successfully completed ranging in depths from 20 m to 448 m.

In the central and western GOA, walleye pollock continued a decade long downward trend in abundance, declining from 783,000 t in 1990 to 593,000 t in 1999 and to only 209,000 t in 2001.  The 2001 pollock biomass which ranked only sixth among all species, exhibited a 41-59 percent split between the western and central GOA respectively.  Compared to the 1999 population where the size distribution included many 35- to 60-cm fish, the 2001 population was composed of three to four times fewer larger fish and twice as many smaller fish less than 20 cm.  Pacific cod, the other important gadid species, ranked sixth in abundance among all species.  Cod declined 10 percent from 285,000 t in 1999 to 256,000 t in 2001 which was evenly divided between the western (51%) and central (49%) GOA.

Over the central and western GOA survey area, arrowtooth flounder was by far the most abundant species with a total biomass estimate of nearly 1.4 million t, a 41 percent increase over the 1999 estimate encompassing the same area.  Nearly 93 percent of the  biomass was from the central GOA survey area. The second-most abundant species was Pacific ocean perch (POP) with a biomass estimate of 712,000 t, a 10 percent increase from the 1999 survey.  POP was relatively evenly distributed between the central (60%) and western (40%) GOA.  Northern rockfish, with a biomass estimate of 344,000 t, ranked third in abundance, a 47 percent increase over the 1999 estimate.  Nearly 74 percent of the northern rockfish biomass was located in the central GOA survey area.  Pacific halibut, the fourth-most abundant species, had a similar biomass distribution with 73 percent of the 347,000  t biomass estimate also occurring in the central GOA.

By Eric Brown.


Midwater Assessment & Conservation Engineering: Triennial Pacific Whiting Survey

Scientists from the MACE program conducted the ninth triennial echo integration trawl (EIT) survey of Pacific whiting (Merluccius productus) off the U.S. and Canadian west coasts from Monterey, California (lat.36ºN) to northern Vancouver Island, British Columbia (lat.50ºN) between 15 June to 29 July 2001.  The purpose of the survey was to collect echo-integration data and midwater and bottom trawl data necessary to determine the distribution, biomass, and biological composition of Pacific whiting.  The survey was part of a collaborative effort with Canadian scientists from the Pacific Biological Station, Nanaimo, British Columbia.

The survey was conducted using the NOAA ship Miller Freeman.  About 3,000 nmi of tracklines were covered, and 76 midwater and 14 bottom trawls were conducted (Figure 1).  A centerboard-mounted 38- and 120-kHz scientific acoustic system was calibrated using standard sphere techniques.  Pacific whiting target strength data were collected using the centerboard transducer system.  A total of 59 Methot trawl hauls were conducted throughout the survey area to examine the distributional patterns and biological characteristics of common macrozooplankton species (e.g., euphausiids).  An intership calibration was performed with the Canadian research vessel W.E. Ricker, which surveyed the area from 50ºN to Dixon Entrance, Alaska.  Vessel-mounted acoustic Doppler current profiler data and surface temperature and salinity measurements were collected continuously throughout the survey.  Vertical profiles of temperature were also collected at selected sites. Ancillary projects included sediment sample collections for a surficial sediment map, fish collections for taxonomy instruction, and collections of near-shore water samples for a biotoxin study.

Pacific whiting echo sign was broadly distributed along the coasts of California and southern Oregon from Monterey Canyon (37ºN) to Heceta Bank (44ºN).  Few whiting were detected north of Heceta Bank, with the only substantial aggregations observed off Barkley Sound, Vancouver Island.  Juvenile whiting (<40 cm) comprised 84 percent of the whiting south of Heceta Bank, whereas adult whiting (>40 cm) comprised 92 percent of the whiting north of Heceta Bank.

By Mike Guttormsen.


Gulf of Alaska Steller Sea Lion/Fishery Interaction Study

Figure 2. Survey trackline used for each pass during the August 2001 echo integration-trawl survey of walleye pollock off the east side of Kodiak Island, Gulf of Alaska.

Center scientists completed the field season for the second year of a fishery interaction experiment during 9-31 August off the east side of Kodiak Island in the Gulf of Alaska. The study is part of a larger program designed to evaluate the effect of commercial fishing activity on the prey availability of walleye pollock to endangered Steller sea lions. The study area consisted of Barnabas and Chiniak troughs, which served as treatment and control sites with commercial fishing allowed in one trough and prohibited in the other, respectively.

The principal objectives for the second year of the experiment were to use standard acoustic survey methods to describe the spatio-temporal variability in pollock abundance and distribution patterns within and between the two troughs over a period of several weeks.  Repeated survey passes (Figure 2 above) were conducted within each trough before and during the fishery to document whether fishery-induced changes occurred in the fish distribution.  Oceanographic data, to characterize the physical environment, were also collected with five current meter moorings, drifters, CTDs (conductivity-temperature- depth data), XBTs (expendable bathythermograph data), a vessel-mounted thermosalinograph, and acoustic Doppler current profiler.

Acoustic backscattering was classified into primarily three groups: adult pollock, juvenile pollock, and capelin (Mallotus villosus).  The adults generally formed loose near-bottom aggregations during the day, whereas the juvenile pollock and capelin formed more discrete aggregations that were higher in the water column.  Preliminary analyses suggested that adult pollock were distributed throughout Chiniak Trough, but largely restricted to the northern half of Barnabas Trough during all passes.  The geographical distributions of the juvenile pollock were similar to those of the adults during all passes.  Capelin were often present over the shallower edges of Chiniak Trough, but were concentrated in the deeper waters within the southern half of Barnabas Trough.

The size distributions of adults were generally similar within each trough, with a prominent mode near 60 cm fork length (FL). The size distributions of juveniles were often characterized with a prominent mode near 20 cm FL, although a second mode also existed between 30-40 cm in some areas.  Capelin ranged in size between 65-140 mm standard length with prominent modes centered around 75-85 and 120 mm.

Analyses are currently underway to determine whether significant changes in fish abundance and distribution patterns were detectable in response to the commercial fishing activities.  Spatial patterns are being explored through spectral analysis and the use of variograms.  In subsequent years repeated surveys will also be conducted following closure of the 1-2 week August fishery to describe the duration that a potential fishery-induced perturbation may persist in the area.

By Chris Wilson.

Shellfish Assessment:  Kodiak Laboratory 2001 NMFS Bering Sea Crab Survey Results

Results of the AFSC’s annual eastern Bering Sea bottom trawl survey for crab and groundfish are used by the NMFS and the ADF&G to determine allowable Guideline Harvest Levels (GHL) for Bering Sea king, Tanner, and snow crabs.  The results of the 2001 survey have been used to determine indices of population abundance that are used to establish the GHLs shown below.  The percent changes in number of crab are relative to the population numbers determined in 2000.  The GHLs are for the combined open-access and CDQ (Community Development Quota) fisheries unless otherwise noted.  The MSST (Minimum Spawning Stock Threshold) levels are established in the fishery management plan for Bering Sea king, Tanner and snow crabs.  For further information, contact Dr. Louis J. Rugolo at 907.481.1715 or Dr. Robert S. Otto at 907.481.1711.

Red king crab (Paralithodes camtschaticus) Bristol Bay
Legal males: 5.1 million crabs; 41percent decrease.
Prerecruits: 4.3 million crabs; 41 percent decrease.
Large females: 21.2 million crabs; 22 percent increase.

Outlook: Abundance of mature and legal males declined sharply owing to mortality, fishery removals, and poor recruitment. Respective indices remain at low historical (1966-P) levels.  Total mature biomass is above MSST, allowing a 10 percent exploitation rate.  Effective spawning biomass and total mature biomass levels are comparable to levels in 2000.

GHL:  7.15 million lb (3,243 metric tons, t), with 6.614 million lb (3000 t) allocated to the open access fishery, and 0.536 million lb (243 t) to the CDQ fishery.  Fishery will open 15 October 2001.

Red king crab (P. camtschaticus) Pribilof District  
Legal males:     1.8 million crabs; 54 percent increase.
Prerecruits:     2.5 million crabs; 587 percent increase.
Large females: 4.0 million crabs; 549 percent increase.

Outlook: Data suggest an increasing trend in abundance of legal males, but caution is urged due to extremely low precision of the estimates. Crabs were highly concentrated. Females are considered to be poorly estimated.  Total mature biomass is above MSST; no fishery threshold has been established in the plan.

GHL:  Fishery will not open in 2001 due to concerns about incidental blue king crab catch, and to low confidence in the abundance indices.

Pribilof Islands blue king crab (P. platypus) Pribilof District
Legal males: 0.4 million crabs; 16 percent decrease.
Pre-recruits: 0.1 million crabs; 48 percent decrease.
Large females: 1.6 million crabs; 17 percent increase.

Outlook: Population is in extremely low historical (1974-P) abundance, and declining trends are not easily detectable.  Total mature biomass is only slightly (6%) above MSST; the male stock is notably below the fishery threshold definition.

GHL:  Fishery will not open in 2001.

St. Matthew blue king crab (P. platypus) Northern District.  
Legal males: 1.1 million crabs; 29 percent increase.
Pre-recruits: 0.6 million crabs; 80 percent increase.
Large females: 0.2 million crabs; 22 percent increase.

Outlook:  Population is in extremely low historical (1976-P) abundance following a steep that commenced in 1997.  Total mature biomass is below MSST; the stock remains in overfished condition.  Female abundance is considered poorly estimated due to their preference for inshore rocky grounds which are untrawlable.

GHL:     Fishery will not open in 2001.

Tanner crab (Chionoecetes bairdi) Eastern District.
Legal males:         6.3 million crabs; 28 percent increase.
Pre-recruits:        17.3 million crabs; 4 percent decrease.
Large females:    13.2 million crabs; 4 percent decrease.

Outlook: Population has declined steeply (86%) since 1990, and remains essentially unchanged over the last 5 years. Legal male abundance is at extremely low historical (1968-P) levels.  Total mature biomass is below MSST; female biomass is below the fishery threshold.  The stock remains in overfished condition.

GHL:     Fishery will not open in 2001.

Snow crab (C. opilio) All districts combined.
Large males: 77.5 million crabs; 2 percent increase.
Small males: 1,791 million crabs; 73 percent increase.
Large females: 1,524 million crabs; 3 percent increase.

Outlook:  Abundance of legal males is unchanged, and remains at low historical (1978-P) levels.  Population is experiencing recruitment of crabs to smaller size groups which may yield legal males in several years conditional on losses to mortality and the fishery.  Total mature biomass is above MSST and the fishery threshold, but significantly (62%) below the rebuilt threshold.

GHL:  30.82 million lb (13,997 t), with 28.51 million lb (12,930 t) allocated to the open access fishery, and 2.31 million lb (1,048 t) to the CDQ fishery.  Fishery will open 15 January 2002.

Hair crab (Erimacrus isenbeckii) All districts combined.
Large males:  1.8 million crabs; 58 percent decrease.
Large females: Not well estimated.

Outlook:  Population has declined sharply (72%) since 1995, and remains in extremely low levels of historical (1978-P) abundance.  Recruitment trends are unclear.  The 2000 fishery in the Northern District performed poorly, yet was targeted at notably larger (2.5-fold) levels of legal male abundance than that estimated in 2001.

GHL:  Fishery will not open in 2001.

By Lou Rugolo.

Fisheries Oceanography Coordinated Investigations (FOCI): Gulf of Alaska Juvenile Pollock and Forage Fish Study

For the second year, FOCI scientists continued to study the mesoscale geographic distribution of young-of-the-year (age-0) walleye pollock and other forage species (capelin and  eulachon) in the western Gulf of Alaska.  Previous estimates of late-summer abundance of age-0 pollock in the GOA have provided early indications of recruitment and insights about large-scale, regional patterns in the geographic distribution of fish density and size. Patterns evident in these data and the complexity of the GOA coastal marine environment suggest that geographic variation among age-0 pollock may exist at smaller scales, such as observed among age-0 density and length data from the western GOA during 1985-88, possibly in response to habitat. Geographic variation in nursery habitat is relevant to recruitment processes because suitable nurseries are the target destination of drifting larvae.  By late summer, the distribution of age-0 juveniles may be indicative of nursery suitability due to their presumed ability to seek out and maintain position in favorable areas. The primary objective of this ongoing study, therefore, is to identify and explain late-summer geographic distribution pattern of age-0 pollock with regard to mesoscale environmental (topography, temperature, salinity) and biological (prey taxa) variation, and in relation to fish growth and feeding success.

During 2-19 September 2001, a grid of 39 stations, representing approximately 10,500 nmi² of the coastal (near-shore and shelf) and slope area between the Shumagin Islands and Kodiak Island, was surveyed aboard the Miller Freeman.  Most grid stations were sampled twice: once at night, when age-0 pollock disperse into the water column and again during the day for comparison.  Samples were collected to quantify the composition and abundance of plankton and micronekton, collect fish samples, and obtain temperature and salinity profiles.  Additional sampling at these and 23 other locations addressed many secondary cruise objectives:

1. compare and evaluate sampling methods
     
2. conduct community analysis of the pelagic community
     
3. determine fish distribution near sea lion rookeries
     
4. perform special requests by other scientists.

The reports for this (MF01-10) and the previous MF00-11 (2-20 September 2000) cruise are posted in the Field Operations section of the FOCI website .  Participation in the cruise by scientists outside the FOCI program, Stan Kotwicki (AFSC), Frank Morado (AFSC), and Maria Ruud (University of Washington), is greatly appreciated.

By Matt Wilson.

Oshoro Maru Visits

Hokkaido University fisheries research vessel Oshoro Maru entering Elliot Bay, Washington

The AFSC and the University of Washington (UW) hosted the Japanese research vessel Oshoro Maru of Hokkaido University during her port-of-call in Seattle. The two universities and the AFSC jointly sponsored a 1-day research symposium “Marine Ecological Studies in the Bering Sea and Eastern North Pacific Ocean” held at the University of Washington.  Members of the Recruitment Processes Program presented four papers at the symposium.  Michael Canino presented a paper titled “Studies of walleye pollock genetic population structure in the North Pacific Ocean and Bering Sea.” Bernard Megrey presented a paper entitled “Modeling marine ecosystem trophodynamics in the North Pacific Ocean.” Former Recruitment Processes program leader Art Kendall presented a paper entitled “Rockfish larvae (Sebastes spp.) In the eastern Bering Sea.”  Lorenzo Ciannelli and Jeff Napp presented a paper entitled “Foraging impact of age-0 walleye pollock around the Pribilof Islands, Bering Sea.”

By Jeff Napp.
  

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AFSC Quarterly
Research Reports
July-Sept 2001