Resource Ecology &
Fisheries Management

RESOURCE ECOLOGY AND ECOSYSTEMS MODELING PROGRAM:

Activities and Research Results

Fish stomachs collected for predation studies totaled 1,036 from the eastern Bering Sea.  Laboratory analysis was performed on 1,640 groundfish stomachs from the eastern Bering Sea, 395 from the Gulf of Alaska-Aleutian Islands, and 542 from the Washington-Oregon-California area.  Eleven observers returned groundfish stomach samples during the quarter.
  

PICES Science 2000

The North Pacific Marine Science Organization (PICES) Ninth Annual meeting was held 18-29 October 2000 in Hakkodate, Japan. More than 500 people registered for 253 oral presentations and many posters sessions given at the meeting.  The main meeting was held at the new Future University.   The keynote lecture was on recent advances and key questions on the Kuroshio-Oyashio ecosystem given by Prof. Takashige Sugimoto. The Science Board symposium topic, “Subarctic gyre processes and their interaction with coastal and transition zones: physical and biological relationships and ecosystem impacts” followed.  Presentations in this session ranged from physical connections between the Subarctic gyres to the biological responses of upper trophic level species and interannual variations in the transition zone chlorophyll front.  The frontal regions in the Oyashio/Kuroshio region was also noted.

Topic sessions were well attended and ranged from basic physical oceanography such as “Large-scale circulation in the North Pacific” to those dealing with environmental quality such as “Science and technology for environmentally sustainable mariculture in coastal areas.”  The topic session on “Short life-span squid and fish as keystone species in the North Pacific marine ecosystems” was particularly appropriate for the PICES meeting in Hakkodate, where we observed the lights of squid fishing boats at night and at day a local artist’s paintings in squid ink. Other topic sessions encompassed the full range of the ecosystem from continuing PICES investigations into the carbon cycle, advancing progress in zooplankton ecology, higher trophic level predators, and continuing the ecosystem synthesis of GLOBEC research.

Interdisciplinary workshops and sessions on understanding climate variability and its effects on ecosystems began before the main scientific meeting with workshops in Tsukuba on CO2 data synthesis and iron fertilization experiment planning.  The Marine Mammal and Bird Advisory Panel met for the first time and held a technical workshop.  The task teams of the PICES GLOBEC Climate Change and Carrying Capacity Program (CCCC) signaled they were entering the final phase of the program with the workshops and task team meetings emphasizing coordination between the task teams and the development of linked biophysical models.

The year 2000 saw continued progress in international collaborative field and laboratory work by the PICES scientific community.  A PICES-sponsored interdisciplinary cruise aboard a research vessel of the Pacific Oceanological Institute took place in the Japan-East Sea.  Integration of the results from the international practical workshop  by scientists of our Marine Environmental Quality Committee’s Working Group 8 took place in one of the PICES topic sessions this year.  Similarly, the Physical Oceanography and Climate Committee’s Working Group 13 on Carbon Dioxide in the North Pacific continued to make significant progress by holding an intercalibration workshop in Tsukuba.  Finally, the PICES-GLOBEC Climate Change and Carrying Capacity Program (CCCC) continued its 2-year study to initiate continuous plankton recorder (CPR) monitoring in the North Pacific and showed interesting results regarding a latitudinal gradient in maturation timing for winter-spring dominant copepods.  PICES continues to discuss how to maintain this monitoring as a long-term PICES effort.

International collaborations of PICES are expanding.  PICES scientists participated in a joint ICES/PICES minisymposium at a meeting of the ICES Zooplankton Ecology working group in spring 2000.  Plans for a jointly sponsored large symposium on zooplankton ecology are now under way.  The North Pacific Anadromous Fish Commission (NPAFC) and PICES jointly sponsored an international workshop on juvenile salmon in Tokyo just after the PICES annual meeting in Hakkodate.  The Census of Marine Life and the International Pacific Research Center will cosponsor with PICES an International Workshop on “Impact of Climate Variability on Observation and Prediction of Ecosystem and Biodiversity Changes in the North Pacific.”  The workshop will help PICES advance in producing a PICES Ecosystem Status Report and begin collaborations to advance a North Pacific monitoring and prediction system that will match the goals of the Census of Marine Life program and the International Oceanographic Commission’s Global Ocean Observing System (GOOS).

In spring 2000, PICES and several international organizations sponsored the Beyond El Niño Conference.  The conference was highly successful and provided substantial evidence for North Pacific ecosystem variability at interannual and decadal time scales and provided insights on the implications of these variations for fishery management.  Selected papers from the conference will be published in a special volume of Progress in Oceanography scheduled for later in 2001.  The results from the 1999 Science Board Symposium on Climate Regime Shifts were published in September 2000 in that same journal.

Many other PICES scientific efforts were documented in 2000 by the publication of results in either the PICES Scientific Report Series, in special journal volumes, or as books.  Two volumes of the PICES Scientific Report series were produced in 2000:  Volume 14 has the results from the activities of Working Group 11 on Predation by Marine Birds and Mammals in the Subarctic North Pacific Ocean, Volume 15 has the proceedings of the 1999 PICES GLOBEC CCCC Program REX and MONITOR workshops and the 2000 MODEL workshop.

Two Working Groups disbanded in 2000 and will be making final preparation for publication of results in 2001.  The Fishery Science Committee Working Group 12 on Crab and Shrimp and Marine Environmental Quality Committee Working Group 8 on Practical Assessment Methodology will publish final results in the PICES Scientific Report Series in 2001.

The PICES-GLOBEC CCCC Program continues work on integrating and stimulating national GLOBEC research efforts in the North Pacific.  The Regional Experiments (REX) Task Team is presently focusing on comparative work on herring in the North Pacific.  They team recently completed a workshop on “Trends in Herring Populations and Trophodynamics” and is planning to expand their work to consider trends in size-at-age for several fish species in 2001.  REX and Basin Scale Studies (BASS) Task Teams are collaborating with MODEL Task Team to begin integrating their work into coupled biophysical models.  MODEL has been very successful in developing a standardized lower trophic level model that can be applied to a variety of regions for intercomparison and coupling with upper trophic level models.  The work on validating their NEMURO lower trophic level model will continue in the coming years.

No new working groups were formed this year. Four working groups, CO2, Micronekton, Ecology of Harmful Algal Blooms, and Climate and Fisheries, are continuing their analyses.  Three advisory panels (Continuous Plankton Recorder, Marine Mammal and Bird, and Iron Fertilization Experiment) are playing important roles in advising the PICES scientific community about research design and improvement in particular areas.

The PICES Science Board has approved many exciting topic sessions for the next annual PICES meeting in Victoria, British Columbia, Canada.  The meeting will be an anniversary celebration of the first decade of science in PICES.  A special science board symposium will celebrate the anniversary with a review of the scientific accomplishments of PICES first 10 years, followed by talks on the future direction of PICES science.

By Pat Livingston.
  

Ecosystem Modeling

A comparison, in collaboration with Russian researchers, of two mass-balance food web models of the 1980s eastern and western Bering Sea shelves revealed structural differences which may arise through the difference in biogeography between the regions.  The eastern Bering Sea ecoregion primarily consists of a wide continental shelf, while the western Bering Sea has an extremely narrow shelf in comparison with its slope area.  As a result, the western Bering Sea possesses approximately twice the level of primary and secondary pelagic production per unit area, as higher production occurs over the slope rather than on the shelf.  However, much of this extra energy is lost between lower and upper trophic levels in the western Bering Sea, due to the differences in supported fish communities in the two regions.  The eastern Bering Sea possesses a larger per-unit-area biomass of most higher trophic level fish guilds.

In both systems, primary production follows two distinct pathways to higher trophic levels: 1) the pelagic pathway, through pelagic zooplankton, forage fish, and cephalopods and 2) the benthic pathway, through benthic zooplankton, infauna, epifauna, and small flatfish.  The transfer of energy through pelagic pathways is proportionately similar in both systems.  However, the flow of energy through the benthic pathways differs substantially, especially between trophic levels 3 and 4.

In the eastern Bering Sea, a complex community of small flatfish species, especially yellowfin sole, rock sole, flathead sole, and Alaska plaice, provides a major energy conduit between benthic invertebrates and higher trophic levels.  These small flatfish may, as a guild, represent a keystone component of the ecosystem on the eastern Bering Sea shelf.  This community is considerably smaller in the western Bering Sea, where an extremely high density of epifauna, such as brittlestars and sea urchins, consume a large proportion of benthic material without passing it up the food chain.  On higher trophic levels (4+), Pacific cod seems to be a keystone predator in both ecosystems.  The determination of keystone species and points in the food web at which top-down and bottom-up control occurs is being explored further through sensitivity analysis of the two food webs.

Additionally, this work brought together data, aided in evaluating data quality, and served as a backdrop for comparing different methods for estimating food consumption in groundfish species.  Sensitivity analyses point to the importance of analyzing food habits and growth rates of fish over their entire life history when measuring their impact on ecosystem dynamics.  A next, important step in this work is to improve the quantification of highly migratory animals, especially marine mammals, in the two models.

By Kerim Aydin.

 

SOCIOECONOMIC ASSESSMENTS PROGRAM:

Economic Analysis of RPAs to Protect Sea Lions and Their Habitat

In a joint effort by the Alaska Fisheries Science Center, the Alaska Regional Office, and NMFS Headquarters, a series of reasonable and prudent alternatives (RPAs) were developed, both to decrease the potential for the Alaska walleye pollock, Pacific cod, and Atka mackerel fisheries to adversely affect Steller sea lions and their habitat and to improve our understanding of the interactions between sea lions and these three fisheries.  The RPAs developed in late November included management measures that would:  1) impose a more conservative control rule for setting the upper limit on total allowable catch (TAC); 2) reopen the Aleutian Islands pollock fishery; 3) close much of the sea lion critical habitat to all pollock, Pacific cod, and Atka mackerel fisheries; 4) establish catch limits for the critical habitat that remains open; and 5) establish seasonal apportionments of each TAC.  Center economists provided estimates of the effects of those management measures on the gross product value through primary processing for those three fisheries.

Three sets of RPA projections were made.  The Model 1 projections address only the RPA effects on TACs and the seasonal apportionment of TACs.  They do not address the effects of the additional area closures and the quotas for the critical habitat areas that would be open under the RPA. Thus, Model 1 projections can be used to estimate only part of the effect of the RPA.  The Model 2 and 3 projections attempt to capture the effects of the changes in the TACs as well as the area closures and critical habitat quotas.

The differences between the projections for Model 2 and Model 3 are due only to the difference in what is assumed about the degree to which catch would be made up from areas closed by the RPA or from catch in the open critical habitat in excess of the RPA quotas.  Under Model 2, it is assumed that none of that catch would be taken elsewhere or in a later season.  Although this assumption may be true under some circumstances for some vessel classes, it is very unlikely to be true in general.  Under Model 3, it is assumed that the percent taken elsewhere would vary by vessel size class or type of at-sea processor.  The assumed percentages are as follows:  1) 0% for catcher vessels under 60 feet; 2) 30% for catcher vessels  60-124 feet; 3) 50% for catcher vessels over 124 feet; 4) 60% for catcher processors; and 5) 40% for motherships.  It is assumed that the made up catch would result from increased catch in the open noncritical habitat areas in the same season.  A sensitivity analysis of the assumed percentages for Model 3 was conducted.

The models were designed to estimate changes in product value resulting from specific RPA induced reductions in catch and reductions in the percent of catch taken during the A (roe) season.  The RPA induced reductions addressed by the models are those resulting from the following:  1) changes in the TACs due to the RPA global control rule and the reopening of the Aleutian Islands area pollock fishery; 2) the additional area closures; and 3) the quotas for the parts of critical habitat that remain open with the RPA.  The potential RPA induced reductions in catch and product value that are not addressed by the models include the following:  1) decreases in catch due to increased fishing and processing costs, decreased ex-vessel and product value per unit of catch, and increased bycatch of prohibited species, groundfish species with very low TACs or seabirds; and 2) decreases in product value per unit of catch due to decreased roe recovery rates or product quality.  The models do not address the increases in harvesting, processing, and management costs that would result from the RPA.

The Model 1 projection, which only reflects the changes in TACs and their seasonal apportionments, is $7.5 million (0 .6%) greater than the status quo projection and $369 million (36.9%) greater than the estimate of the 1998-99 average product value.  The Model 1 projection is greater than the status quo projection because the projected increases in catch and product value resulting from reopening the Aleutian Islands pollock fishery under the RPA more than offset the effects of the decrease in the GOA pollock TAC under the RPA.

The Model 2 projection is $401.4 million (29.5%) less than the status quo projection and $40 million (4.0 percent) less than the estimate of the 1998-99 average product value.  The Model 3 projection is $224.6 million (16.5%) less than the status quo projection and $137 million (13.7%) greater than the estimate of the 1998-99 average product value.

The projections are based on 1999 data for product prices, product mix, and the distribution of catch by period, type of area, processing sector, gear, and vessel size class.  Data for 2000 were not available.

The quantitative estimates were of gross, not net, product value.  The decrease in product value associated with a decrease in catch will tend to overstate the decrease in net product value, because typically harvesting and processing costs would also be reduced.  However, if the RPA would not decrease catch but would increase harvesting and processing costs, the decrease in net product value would exceed the decrease in gross product value.  The lack of cost data prevents an assessment in terms of net product value.

None of the model projections address changes in fishery participant actions that may mitigate some of the adverse effects of the RPA.  Such actions may include changing effort allocation across seasons, areas, or gear types.

In addition to providing projected changes in product value, the analysis identified a variety of other types of effects the RPA would be expected to have.

By Joe Terry.
  

Age and Growth Program

Estimated production figures for 1 January  2000 to 30 December.

Total production figures were 28,370 with 6,979 test ages and 343 examined and determined to be unageable.

By Dan Kimura.

 

U.S. GROUNDFISH OBSERVER PROGRAM

During the fourth quarter of 2000, 171 observers were trained, briefed, and equipped for deployment to fishing and processing vessels and shoreside plants in the Gulf of Alaska, Bering Sea, and Aleutian Islands.  They sampled aboard 161 fishing and processing vessels and at 14 shoreside processing plants.  The observers were trained or briefed in various locations.  The Alaska Fisheries Science Center (AFSC) Observer Program in Seattle trained 26 first time observers and another 18 observers with prior experience were briefed at this site.  The University of Alaska Anchorage (UAA) Observer Training Center briefed 79 observers and another 35 first-time observers were trained.  No observers were briefed at the Observer Program’s field offices in Dutch Harbor and Kodiak during the fourth quarter of 2000, and 13 observers were excused from briefing because they had just completed a cruise successfully and were returning immediately to the field.  The fourth quarter 2000 observer workforce thus comprised 36% new observers and 64% experienced observers.

The Observer Program conducted a total of 216 debriefings during the fourth quarter of 2000. Two debriefings were held in Kodiak, three in Dutch Harbor, 46 in Anchorage; and 165 were held in Seattle.

The statistics for the entire year of 2000 are as follows:

 

Highlights of 2000

An extensive, independent review of the Observer Program began in late 1999 by Marine Resources Assessment Group (MRAG) Americas, Inc.  The purpose of the review was to provide recommendations for changes in program operations and organization which might improve the program’s ability to meet its mission and goals.  Their final report along with a response from the AFSC was made available to the North Pacific Fishery Management Council at its meeting in September 2000. Two key recommendations in the MRAG report were 1) reestablishing  program goals and objectives and 2) developing a contractual relationship between NMFS and the observer provider companies to eliminate any real or perceived conflicts of interest between the observer companies and the fishing fleet they service.

In addition to the MRAG review, the Observer Program was also reexamined in 2000 along with all other NMFS observer programs, through the annual NMFS management control review (MCR) process.  The newly established National Observer Program Advisory Team (NOPAT) was actively involved in this endeavor.  NOPAT is made up of representatives from all NMFS regional offices, science centers, and observer programs and is coordinated through the National Observer Program Office of NMFS.
  

Observer Program Cadre Takes Shape:

New office space in Anchorage was designed, constructed, and leased in the federal building annex during 2000, to house 10 new Observer Program employees.  These new employees along with the existing two positions in Anchorage will make up the Observer Program “Cadre.”  The cadre is an inherently flexible unit of employees that can be deployed as needed to ports throughout Alaska.  They help to increase the Observer Program’s presence in the field and allow for more communication between NMFS, observers, and the fishing industry.
  

Second Biennial U.S.-Canada Observer Program Workshop:

Several Observer Program staff participated in the second biennial U.S.-Canada Fisheries Observer Program Workshop in St. John’s Newfoundland in June 2000.  The first workshop was hosted by the AFSC in 1998 and was developed to bring together some of the key organizations responsible for the design, management and delivery of at-sea fisheries observer programs in the United States and Canada.  The second workshop was expanded in scope to include greater representation from the fishing industry and observers.
  

CDQ and AFA Fisheries:

Implementation of an expanded Community Development Quota (CDQ) program and implementation of provisions of the recently enacted American Fisheries Act (AFA) continued during 2000.  The CDQ program was developed for the purpose of allocating fishery resources to eligible Western Alaska communities to provide the means for starting or supporting commercial fishery activities that would result in ongoing, regionally based, commercial fishery, or related businesses.  CDQ was initiated in 1992 with pollock and expanded to include fixed gear halibut and sablefish in 1995.  In 1998, it was further expanded to include multiple species of groundfish and crab (MSCDQ).  In 1999, NMFS was responsible for monitoring the groundfish (including pollock and sablefish) and halibut CDQs and the State of Alaska was responsible for monitoring the crab CDQs.  This division of responsibility continued into 2000.

By Bob Maier.

 

STATUS OF STOCKS AND MULTISPECIES ASSESSMENT PROGRAM:

2000 Stock Assessment Summaries

BSAI Walleye Pollock		BSAI Pacific Cod
BSAI Yellowfin Sole		BSAI Greenland Turbot
BSAI Arrowtooth Flounder		BSAI Rock Sole
BSAI Flathead Sole		BSAI Other Flatfish
BSAI Pacific Ocean Perch		BSAI Other Red Rockfish
BSAI Other Rockfish		AI Atka Mackerel
BSAI Squid & Other Species		GOA Pollock
GOA Pacific Cod		GOA Flatfish
GOA Arrowtooth Flounder		GOA Atka Mackerel

The Status of Stocks and Multispecies Assessment Program (SSMA) completed stock assessments for major groundfish stocks in the Bering Sea, Aleutian Islands region, and Gulf of Alaska.  Information from a variety of sources were used including:  survey biomass estimates provided by the RACE Division, fishery catch estimates from the NMFS Alaska Regional Office, fishery dependent biological samples from the REFM Observer Program and fishery and survey age composition data from the REFM Age and Growth Program.  Final SAFE (Stock Assessment and Fishery Evaluation) reports were prepared for the NPFMC meetings.  The NPFMC used the assessments to recommend levels of Acceptable Biological Catch (ABC) for the 2001 fishing seasons.

Scientists from the SSMA Program participated in preparation of many of the assessment chapters for the Gulf of Alaska and Bering Sea-Aleutian Islands regions.  Scientists from the Auke Bay Laboratory, the RACE Division, and the Alaska Department of Fish and Game also authored or contributed to the development of the SAFE chapters.

In 2000, 14 stocks or stock complexes in the Bering Sea-Aleutian Islands (BSAI) were assessed:  walleye pollock, Pacific cod, yellowfin sole, Greenland turbot, rock sole, flathead sole, arrowtooth flounder, other flatfish (includes 16 species of flatfish), eastern Bering Sea (EBS) Pacific ocean perch, Aleutian Islands Pacific ocean perch, other red rockfish, sablefish, Atka mackerel, and “other species” (see Table 1 for species included in stock complexes).  In the Gulf of Alaska, 10 stocks or stock complexes were assessed:  walleye pollock, Pacific cod, arrowtooth flounder, other flatfish, Pelagic shelf rockfish, slope rockfish, demersal shelf rockfish, sablefish, Atka mackerel, and other species.  Major findings for selected assessments are summarized below, grouped by management area and species.

The values presented below reflect information found in the SAFE documents developed by the NPFMC’s Plan Teams for groundfish fisheries in the Gulf of Alaska and Bering Sea-Aleutian Islands
(Table 2 and Table 3).  It should be noted that the Plan Teams’ ABC and TAC recommendations are reviewed by the NPFMC advisory bodies and the Council recommends the final TAC.  Thus, the values presented below may differ from the final Council recommendations.  For information on final groundfish specifications, please consult the NPFMC’s web page at http://www.fakr.noaa.gov/npfmc or contact the authors.
  

BSAI Walleye Pollock

This year’s walleye pollock assessment features new data from the 2000 fishery and two surveys:  the bottom trawl and echo-integration trawl surveys.  The 2000 bottom trawl survey estimated a biomass of 5,140,000 metric tons (t), an increase of 44% relative to the 1999 estimate.  This follows a 61% increase in 1999 relative to the 1998 estimate.  The 2000 echo-integration trawl survey estimated a biomass of 3,005,000 t, a decrease of 7% relative to the 1999 estimate and following an increase of 27% from the 1997 estimate, the last year an echo-integration trawl survey was conducted in this region.  Ten alternative models were presented to the Council, all of which follow the statistical age-structured approach that was used last year to set ABC for 2000.  Of the 10 models presented, the stock assessment author based his recommendations for 2001 on Model 1, which uses the commercial fishery selectivity pattern from 1999 to make projections of future catch and stock size.  This model is most similar to the model used by the Plan Team last year to recommend the 2000 ABC, except that the selectivity estimates are based only on estimates from 1999, since the establishment of cooperatives and new regulations may be best reflected in the most recent year of fishery data.  In addition, this year’s model runs all include the foreign fishery CPUE data from 1965 to1976.

Last year, the scientific and statistical committee (SSC) determined that reliable estimates of B_MSY and the probability density function for F_MSY exist for this stock, and that EBS walleye pollock qualified for management under Tier 1.  The maximum permissible value of F_MSY under Tier 1a is 0.71, the harmonic mean of the probability density function for F_MSY.  A fishing mortality rate of 0.71 translates into a 2001 catch of 2,125,000 t, which would be the maximum permissible ABC under Tier 1a.  Last year, the senior assessment author and Plan Team recommended setting ABC at a lower value, specifically, the maximum permissible level that would be allowed under Tier 3.  The 2001 catch associated with a fishing mortality rate of 0.49 is 1,842,000 t, a 13% reduction from the maximum permissible level under Tier 1.

The 2000 bottom trawl survey of the Aleutians Islands region resulted in a biomass estimate of 106,000 t, an increase of 13% relative to the 1997 estimate.  The 1997 estimate previously was 106,000 t, but was revised this year to 94,000 t due to discrepancies found in strata definitions.  The 1997 stock assessment concluded that the model which had been used to recommend ABC for 1997 was no longer reliable due to the confounding effect of immigration from other areas, and the SSC determined that Aleutian pollock qualified for management under Tier 5. This gives an ABC based on Tier 5 (2000 survey biomass  × M ×  0.75) of 23,750 t at a biomass of 105,554 t (with M = 0.3). The overfishing level (OFL)  based on Tier 5 (2000 survey biomass × M) gives 31,666 t.

The 2000 hydroacoustic survey of the Bogoslof  region resulted in a biomass estimate of 301,000 t.  The maximum permissible 2001 ABC is 45,200 t (= 301,000 t × M × 0.75), which is the Plan Team’s recommended ABC and for 2001 OFL is 60,200 t (= 301,000 t  × M).
  

BSAI Pacific Cod

The 2000 assessment updated last year’s assessment, incorporating new catch and survey information.  This year’s EBS bottom trawl survey resulted in a biomass estimate of 528,000 t, a 9% decrease from last year’s estimate and the lowest observed value for the survey.  The Aleutian Islands were surveyed in 2000, the biomass increased 63% from 1997.  Estimates of abundance are somewhat higher for the 2000 assessment compared to the 1999 assessment.  For example, estimated 2001 spawning biomass for the BSAI stock is 369,000 t, up about 10% from last year’s F_ABC projection for 2001.   The SSC has determined that reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and that this stock qualifies for management under tier 3 of the BSAI Groundfish fishery management plan.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 389,000 t, 0.29, and 0.35, respectively.  Fishing at a rate of 0.28 is projected to result in a 2001 spawning biomass of 369,000 t, and solves the equation for the maximum permissible value of F_ABC under Tier 3.  Because projected biomass for 2001 is less than B_40%, Pacific cod qualify for management under sub-tier “b” of Tier 3.  Fishing at an instantaneous rate of 0.28 is projected to result in a 2001 catch of 214,000 t, which is the maximum permissible ABC under Amendment 56.  The 2001 ABC was set at 188,000 t, 12% below the maximum permissible level.  This recommendation is based on a risk-averse optimization procedure which considers uncertainty in the estimates of the survey catchability coefficient and the natural mortality rate in the computation of an F_40% harvest level.  The Bayesian meta-analysis which has formed the basis for a risk-averse ABC recommendation in each of the last 4 years was not performed for the present assessment.  Instead, the ratio between last year’s recommended F_ABC and F_40% (0.87) was assumed to apply this year as well.

The 12% reduction from the maximum permissible ABC is justified not only on the basis of these decision-theoretic concerns, but also because estimated spawning biomass from the model has declined continuously since 1987 and because four of the last five year classes (assessed at age 3) appear to have been well below average.  A 2001 catch of 188,000 t would represent a decrease of 2% relative to the 2000 ABC of 193,000 t, the same direction as the 9% decrease in the trawl survey biomass estimate.  Spawning biomass projected for 2001 is 38% of it’s unfished level.  Spawning biomass is projected to decline through 2004.  ABC reaches a minimum of 135,000 t in 2003.  A 2001 catch of 188,000 t corresponds to a fishing mortality rate of 0.24, below the value of 0.28 which constitutes the upper limit on F_ABC under Tier 3b.  The recommended OFL was determined from the Tier 3b formula, where fishing at a rate of 0.32 gives a 2001 catch of 248,000 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
  

BSAI Yellowfin Sole

This year’s EBS bottom trawl survey resulted in a biomass estimate of 1,580,000 t, an increase of 21% from last year’s survey, but still a 32% decline from 1998.  The sharp decrease in 1999 was attributed in part to cold water which might have decreased availability.  However, both the 1999 and 2000 trawl surveys’ lower estimates may be due to the survey being performed earlier, when a significant portion of the stock is still at the spawning grounds in shallow water.  Extra tows were done outside the normal trawling area (in shallow waters), and concentrations of yellowfin sole were encountered.  An AI trawl survey was also performed and caught yellowfin sole in only two tows, of less than 20 kg each.  The biomass estimate for the AI is not included in the model due to the relatively low catch.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and the stock qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 502,000 t, 0.11, and 0.13, respectively.  Given that the projected 2001 spawning biomass of 742,000 t exceeds B_40%, the ABC and OFL recommendations for 2001 were calculated under sub-tier “a” of Tier 3.  The author recommended setting F_ABC at the F_40% (=0.11) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2001 ABC of 176,000 t.  The OFL was determined from the Tier 3a formula, where an F_35% value of 0.13 gives a 2001 OFL of 209,000 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.  The yellowfin sole stock continues to decline, as do several other flatfish stocks, despite low exploitation rates.  The decline is due to the low recruitment in the last decade.
  

BSAI Greenland Turbot

The current assessment updated last year’s assessment, incorporating new catch and survey information.  The SSC has determined that reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and that this stock qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35%  from the present assessment are 81,200 t, 0.26, and 0.32, respectively.  Projected spawning biomass for 2001 is 136,000 t, placing Greenland turbot in sub-tier “a” of Tier 3.  The Plan Team notes that the ratio of spawning biomass to B_40% has changed slightly since last year’s assessment.  The maximum permissible value of F_ABC under Tier 3a is 0.26.  A fishing mortality rate of 0.26 translates into a 2001 catch of 27,400 t, which would be the maximum permissible ABC under Amendment 56.  The recommendation to set the 2001 ABC at a value substantially less than the maximum permissible, using F_ABC = 0.25 × max F_ABC, which results in a 2001 ABC of 8,400 t was accepted  for the following reasons: 1) the estimated age 1+ biomass has trended downward continually since 1972; 2) the seven most recent age-1 recruitments constitute seven of the lowest eight values in the entire time series; and 3) if the maximum permissible ABC of 27,400 t were actually caught, this would constitute the highest catch since 1983, even though spawning biomass in 2001 is projected to be less than half of what it was in 1983.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
  

BSAI Arrowtooth Flounder

This year’s EBS bottom trawl survey resulted in a biomass estimate of 340,000 t, a 29% increase relative to last year’s estimate and similar to the 1998 trawl survey.  The 2000 AI trawl survey resulted in a biomass estimate of 93,500 t, which represents 22% of the BSAI arrowtooth flounder combined biomass estimate from the trawl surveys.  The biomass estimate for the AI is not included in the model due to the low relative catch.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock and, therefore, it qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35%  from the present assessment are 183,000 t, 0.23 and 0.28, respectively.  Given that the projected 2001 spawning biomass of 458,000 t exceeds B_40%, the ABC and OFL recommendations for 2001 were calculated under sub-tier “a” of Tier 3.  The author recommended setting F_ABC at the F_40% (=0.23) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2000 ABC of 117,000 t.  The OFL fishing mortality rate is computed under Tier 3a, F_OFL = F_35% = 0.29, and translates into a 2000 OFL of 141,500 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

The effort in the fishery increased this year due to a developing market in Japan for arrowtooth flounder, though still a low exploitation rate (< 0.02).  The arrowtooth flounder stock continues to decline, as does several other flatfish stocks, due to the low recruitment in the last decade.
  

BSAI Rock Sole

This year’s EBS bottom trawl survey resulted in a biomass estimate of 2,130,000 t, a 26% increase relative to last year’s estimate, and very similar to the 1998 trawl survey estimate.  An Aleutian Island trawl survey was also performed and resulted in a biomass estimate of 46,000 t, which represents only 2% of the BSAI rock sole combined biomass estimate from the trawl surveys.  The biomass estimate for the AI is not included in the model due to the low relative catch.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and it qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35%  from the present assessment are 285,000 t, 0.16, and 0.19, respectively.  Given that the projected 2001 spawning biomass of 676,000 t exceeds B_40%, the ABC and OFL recommendations for 2001 were calculated under sub-tier “a” of Tier 3.  The author recommended setting F_ABC at the F_40% (=0.16) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2001 ABC of 230,000 t.  The OFL was determined from the Tier 3a formula, where an F_35% value of 0.19 gives a 2001 OFL of 273,000 t.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

The rock sole stock continues to decline, as do several other flatfish stocks, due to the low recruitment in the last decade.
  

BSAI Flathead Sole

The present assessment includes significant changes from last year’s assessment, including use of AD Model Builder as a modeling platform and incorporation of new catch and survey information.  The model included a new, simpler selectivity function that yielded a slightly lower, though smoother curve.  The new AD Model Builder estimates tested favorably against the previously used Synthesis Model.  Furthermore, there was an Aleutian Island trawl survey in 2000, and those data and estimates are combined here with the EBS data.  This year’s EBS bottom trawl survey resulted in a biomass estimate of 399,000 t, a 1% increase relative to last year’s estimate.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock, and it qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 134,000 t, 0.30, and 0.38, respectively.  Given that the projected 2001 spawning biomass of 268,000 t exceeds B_40%, the ABC and OFL recommendations for 2001 were calculated under sub-tier “a” of Tier 3.  The author recommended setting F_ABC at the F_40% (=0.30) level, which is the maximum permissible level under Tier 3a.  Projected harvesting at the F_40% level gives a 2001 ABC of 84,000 t.  The OFL was determined from the Tier 3a formula, where an F_35% value of 0.38 gives a 2001 OFL of 102,000 t. Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
  

BSAI Other Flatfish Complex

The present assessment updated last year’s assessment, including use of AD Model Builder as a modeling platform for Alaska plaice only.  The new model further was improved by using individual CVs of surveys to weight surveys each year as a replacement for the average CV values used previously.  The assessment also incorporates new catch and survey information.  This year’s EBS bottom trawl survey resulted in biomass estimates of 444,000 t for Alaska plaice and 80,000 t for the remaining species in the “other flatfish” complex.  The other “other flatfish” are Dover sole (1%), rex sole (21%), longhead dab (17%), Sakhalin sole (<1%), starry flounder (58%), butter sole (2%) and English sole (<1%).  This represents a decrease of 19% in Alaska plaice and an increase of 15% of “other flatfish” relative to last year’s estimates.  Note that last year, plaice increased and “others” decreased.  The population of Alaska plaice appears to be gradually declining, and there has been no apparent strong recruitment recently.

Reliable estimates of B_40%, F_40%, and F_35% exist for this stock complex, and it qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 111,000 t (Alaska plaice only), 0.29, and 0.36, respectively.  Given that the projected 2001 spawning biomass (Alaska plaice only) of 217,000 t exceeds B_40%, the Plan Team’s ABC and OFL recommendations for 2001 were calculated under sub-tier “a” of Tier 3.  Because 85% of the “other flatfish” category is Alaska plaice and the assessment author calculates plaice separately, the author recommended setting the ABC and OFL for Alaska plaice separately from the other species.  For Alaska plaice, the author recommended F_ABC at the F_40% level (=0.29), which is the maximum allowable under Tier 3a.  Projected harvesting at the F_40% level gives a 2001 ABC of 122,000 t for Alaska plaice.  For the remaining species in the flatfish complex, the author recommended F_ABC at the F_40% level (=0.30), which is the maximum allowable under Tier 3a.  Projected harvesting at the F_40% level gives a 2001 ABC of 18,000 t for “other” non-plaice flatfish.  As with the ABC, the plan recommends separating Alaska plaice from “other” flatfish for OFL. The Plan Team’s OFL was determined from the Tier 3a formula, where for Alaska plaice an F_35% value (=0.35) gives a 2001 OFL of 147,000 t.  For the “other flatfish” species, the author gave an F_35% value (=0.38) giving a 2001 OFL of 22,000 t. Model projections indicate that this stock complex is neither overfished nor approaching an overfished condition.
  

BSAI Pacific Ocean Perch (POP)

• EBS:

The present assessment updated last year’s assessment, incorporating new catch information. Reliable estimates of B_40%, F_40%, and F_35% exist for this stock and qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 21,500 t, 0.049, and 0.058, respectively.  Projected spawning biomass for 2001 is 18,100 t, placing POP in the EBS in sub-tier “b” of Tier 3.  The maximum F_ABC value allowed under Tier 3b is computed as follows:

   F_ABC  £  F_40%  ×  (B₂₀₀₁  /  B_40%  -  0.05)  /  (1-0.05)  = 
   0.049  ×  (18,100  /  21,500  -  0.05)  /  0.95  =  0.040.

Projected harvesting at a fishing mortality rate of 0.04 gives a 2001 catch of 1,730 t, which is the recommended ABC (last year’s ABC was set using a higher fishing mortality rate, 0.054, in part because last year’s B_40% estimate of 26,200 t was higher than this year’s estimate of 21,500 t).

The OFL fishing mortality rate is computed under Tier 3b as follows:

   F_OFL  =  F_35%  ×  (B₂₀₀₁  /  B_40%  -  0.05)  /  (1-0.05)  =
   0.058  ×  (18,100  /  21,500  -  0.05)  /  0.95  =  0.048.

Projected harvesting at a fishing mortality rate of 0.048 gives a 2001 catch of 2,040 t, which is the recommended OFL.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.

• AI:

The present assessment is a straightforward update of last year’s assessment, incorporating new catch information and age composition data.  Reliable estimates of B_40%, F_40%, and F_30% exist for this stock and qualifies for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 89,100 t, 0.062, and 0.073, respectively.  Projected spawning biomass for 2001 is 84,900 t, placing true POP in the AI region in sub-tier “b” of Tier 3.  The maximum F_ABC value allowed under Tier 3b is computed as follows:

   F_ABC  £  F_40%  ×  (B₂₀₀₁  /  B_40%  -  0.05)  /  (1-0.05)  =
   0.062  ×  (84,900  /  89,100  -  0.05)  /  0.95  =  0.059.

Projected harvesting at a fishing mortality rate of 0.059 gives a 2001 catch of 10,200 t, which is the Plan Team’s recommended ABC.  The ABC is apportioned among AI subareas based on survey distribution as follows:  Western AI = 46.5%, Central AI = 25.1% , and Eastern = 28.4%, corresponding to 4,749 t (W), 2,563 t (C), and 2,900 t (E).

The OFL fishing mortality rate is computed under Tier 3b as follows:

   F_OFL  =  F_35%  ×  (B₂₀₀₁  /  B_40%  -  0.05)  /  (1-0.05)  =
   0.073  ×  (84,900  /  89,100  -  0.05)  /  0.95  =  0.069.

Projected harvesting at a fishing mortality rate of 0.069 gives a 2001 catch of 11,800 t, which is the recommended OFL.  Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
  

BSAI Other Red Rockfish

This year separate chapters were prepared for POP and the combined “other red rockfish” for presentation to the NPFMC.  It was felt that separate chapters would improve the clarity of the assessment and facilitate better understanding of the methodology used and the results obtained.  The authors also examined the possibility of specifying area-specific OFLs, ABCs, and TACs for the shortraker/rougheye complex and a combined-area OFL, ABC, and TAC for the northern/sharpchin complex.  The assessments included catch and survey data by individual species to determine if differential harvest rates exist.

Through 2000, the other red rockfish complex was split into northern/sharpchin and rougheye/shortraker groups in the AI region, and a combined other red rockfish group for the EBS.  The assessment authors provided an assessment for these species groups by incorporating recent catch data and the 2000 AI survey results.  Splitting the complexes was needed because when managed as a species complex, there is a risk that one stock would be fished disproportional to its abundance, resulting in overfishing of that stock.  This is especially true when one species has a higher value to the fishery than the other species.  This has happened in the other red rockfish complex, and the assessment appendix showed that on a species basis, catches have sometimes exceeded what OFL would have been.  This occurred for rougheye rockfish in the AI in 1997 and for northern rockfish in the EBS in 2000.  Establishing ABCs on a species by species basis would help prevent overfishing.  There are also immediate economic and management issues to be addressed by splitting out the other red rockfish category.  Quite simply, the low abundance of rockfish in the EBS would be very constraining to the fleet. The low OFL calculated for the 2001 EBS “other red rockfish” complex (180 t) could greatly impact the 2001 fisheries.  Note that the 2000 catch was 228 t even though it was on bycatch status all year.  Other target fisheries could be shut down, or prohibited to retention, to prevent the OFL from being exceeded.

For each species, the F_ABC  was set at the maximum value allowable under Tier 5, which is 75% of M.  Accepted values for M are:  rougheye rockfish - 0.025, shortraker rockfish - 0.030, and northern rockfish - 0.060.  Multiplying these rates by the best estimates of species-specific biomass gives the following 2001 ABCs:

Note that sharpchin rockfish are at the extent of their range in the BSAI and are not common.  Therefore, no specifications for this species are recommended.

To prevent topping off of northern rockfish, rougheye, and shortraker rockfish, these species may be prohibited to retention in the EBS at the beginning of the year.  Another possibility would be to reduce maximum retainable bycatch levels from the current 15%.

The OFL was determined from the Tier 5 formula, where setting F_OFL= M for each species gives 2001 OFLs:

As Tier 5 stocks, it is not possible to determine whether any species in the EBS “other red rockfish” complex is overfished or whether it is approaching an overfished condition.
  

BSAI Other Rockfish Complex

The present assessment is updated and expanded from last year’s assessment.  Traditionally, the biomass estimates (split according to management area) from all bottom trawl surveys (EBS shelf/slope and AI) are averaged over all years to obtain the best estimates of biomass for the species in this complex.  Summed over the species in the complex, this procedure produces a biomass estimate of 6,880 t in the EBS and a biomass estimate of 12,900 t in the AI.  The great majority of this biomass is comprised of thornyhead rockfish.  Last year, the SSC determined that a reliable estimate of the natural mortality rate (M) existed for the species in this subcomplex, and that “other rockfish” in the EBS and AI is qualified for management under Tier 5 of the BSAI Groundfish FMP.  The accepted estimate of M for these species in both areas is 0.07.  The recommended F_ABC was set at the maximum value allowable under Tier 5, which is 75% of M, or 0.053.  Multiplying this rate by the best estimate of complex-wide biomass gives a 2001 ABC of  361 t in the EBS and 676 t in the AI.

The OFLs were determined from the Tier 5 formula, where setting F_OFL = M gives a 2001 OFL of 482 t in the EBS and 901 t in the AI.  As a Tier 5 stock complex, it is not possible to determine whether the “other rockfish” complex is overfished or whether it is approaching an overfished condition.

The assessment authors provided catch and survey data for individual species within this complex.  Notably, about 90% of this complex is composed of shortspine thornyheads according to survey data.  However, the commercial fishery in the AI takes mostly dusky rockfish and this raised some concerns about the potential for localized overfishing.  For example, the catch in 2000 of dusky rockfish in the eastern AI region was 171 t, whereas the estimated biomass was 522 t.
  

AI Atka Mackerel

New catch data, survey biomass estimates, 1999 fishery and 2000 survey age data were incorporated into the model.  The SSC has determined that this stock is qualified for management under Tier 3 of the BSAI Groundfish FMP.  The updated point estimates of B_40%, F_40%, and F_35% from the present assessment are 154,000 t, 0.35, and 0.42, respectively.  Projected spawning biomass for 2001 is 159,000 t, placing Atka mackerel in sub-tier “a” of Tier 3.  The maximum F_ABC value allowable under Tier 3a is F_40% (0.35).  Projected harvesting at a fishing mortality rate of 0.35 gives a 2001 catch of 128,000 t, which is the maximum permissible value of ABC under Tier 3a.   The assessment authors recommend setting F_ABC at a value of 0.19 would give a 2001 catch of 58,700 t.  The F_ABC value was computed from the F_40% value by adjusting the F_40% value based on the CV of the survey biomasses, which results in a 44% downward adjustment of F.  Stock size continues to decline, current biomass is about 40% of the peak estimated in the early 1990s. The five surveys from 1986 through 2000 are highly variable, the biomass estimates for a 95% confidence interval are very large in several cases ranging from zero to more than double the estimate.  Atka mackerel are difficult to survey, applying the model’s estimate of F_40% to the model’s estimate of next year’s biomass does not address the substantial uncertainty surrounding these biomass estimates. The adjustment method incorporates a  measure of uncertainty regarding the survey estimates into the harvest strategy.

To apportion ABCs among areas, the authors used a weighted average of the four most recent survey estimates of the distribution of the biomass, which gives the greatest weight to the 2000 survey.  When applied to the recommended ABC of 58,700 t, this formula gives the following subarea-specific ABCs:  EBS and Eastern Aleutians = 6,600 t (11.2%), Central Aleutians = 28,500 t (48.5%), Western Aleutians  = 23,600 t (40.2%).  The Plan Team discussed other possible weighting schemes including a three survey, unweighted average.  The OFL was determined from the Tier 3a formula, where an F_35% value of 0.42 gives a 2001 OFL of 138,000 t. Model projections indicate that this stock is neither overfished nor approaching an overfished condition.
  

BSAI Squid and Other Species Complex

The squid assessment updated last year’s assessment by incorporating new catch information.  The squid stock is managed under Tier 6, OFL is set equal to the average catch from 1978 through 1995, and ABC is constrained to be no greater than 75% of OFL.  The average catch from 1978 through 1995 was 2,620 t.  The maximum permissible value of ABC for 2001, therefore, is 1,970 t.  The “other species” assessment is an update of last year’s assessment, incorporating new catch and survey biomass information. The 2001 ABC was set equal to the average catch, which is 26,500t.
  

GOA Pollock

Model exploration focused on improving treatment of the Shelikof Strait echo integration trawl (EIT) survey by splitting the time series into two catchability periods to account for the use of a new acoustic system in 1992.  In addition, a method for using the EIT survey estimates of age-1 abundance in stock projections was evaluated.  Projected exploitable biomass for age-3+ pollock in 2001 is 699,000 t as estimated from the current assessment model.  Projected female spawning biomass in 2001 for the Western, Central and West Yakutat areas is 202,800 t, which is below the B_40% value of 247,000 t.  This places GOA pollock in Tier 3b. The ABC for 2001 was 99,350 t for the Western, Central, and West Yakutat areas.  For pollock in Southeast Alaska (East Yakutat and Southeastern areas), the ABC recommendation is unchanged at 6,460 t.

Pollock in the Southeast Outside and East Yakutat areas fall into a Tier 5 assessment.  Under this approach, 2001 ABC is 6,460 t, based on exploitable biomass of 28,710 t as derived from catch per unit effort (CPUE) data during the 1999 GOA trawl survey and a natural mortality estimate of 0.30.  The OFL is 8,610 t.  The pollock catch in the pooled Southeast Outside and East Yakutat areas have never exceeded 100 t during 1991-2000.
  

GOA Pacific Cod

Only size composition and total catch data from the 1999 and January-August 2000 commercial fisheries (Federal and state) were incorporated into the 2000 Pacific cod assessment model.  The Bayesian metanalysis that has formed the basis for a risk-averse ABC recommendation in each of the last 4 years was not performed.  Instead, the ratio between last year's recommended F_ABC and F_40% (0.87) was assumed to apply this year as well.

The estimated 2001 spawning biomass for the GOA stock is 93,800 t, down about 15% from last year's estimate for 2000 and down about 7% from last year’s F_ABC projection for 2001.  The estimated 2001 total age 3+ biomass for the GOA stock is 526,000 t, down about 7% from last year's estimate for 2000 and down about 5% from last years F_40% projection for 2001.  While the population is still projected to decrease, it is still above the estimated B_40% level.

The author's recommended 2001 ABC for the GOA stock was 67,800 t, obtained by applying the ratio of 0.87 to the updated model fit.  This is down about 11% from last year’s recommendation for 2000 and down about 5% from last year's F_ABC projection for 2001.  The estimated 2001 OFL for the GOA stock is 91,200 t, down about 11% from last year’s estimate for 2000.  Apportioning  the ABC between regulatory areas in proportion to the biomass estimates from the most recent trawl survey, results in the following: Western-36% , Central-57%, and Eastern-7%, which would result in 24,400 t, 38,650 t, and 4,750 t, respectively.

Area Apportionments of GOA  Flatfish ABCs for 2001
	WESTERN	CENTRAL	WYAK	EYAK/ SEO	TOTAL
Deepwater flatfish	280	2,710	1,240	1,070	5,300
Rex sole	1,230	5,660	1,540	1,010	9,440
Shallow-water flatfish	19,510	16,400	790	1,160	37,860
Flathead sole	8,490	15,720	1,440	620	26,270
TOTAL	29,510	40,490	5,010	3,860	78,870

GOA Flatfish

The flatfish group is subdivided into deepwater flatfish, rex sole, shallow-water flatfish, and flathead sole.  The 2001 exploitable biomass for each category is based on a delay difference model that includes estimates of growth, natural mortality, and recruitment, as well as biomass estimates from the 1996 and 1999 bottom trawl surveys.  ABC and OFL were calculated by species, with individual species identified as tier 4, 5, or 6 depending upon the available data.  With catch being the only updated information, estimates of exploitable biomass and ABC totaled 655,680 t and 78,870 t, respectively, the same values as in the previous assessment. ABCs are apportioned among the regulatory areas according to biomass distributions from the 1999 survey.
  

GOA Arrowtooth Flounder

The 2001 exploitable biomass of 1,586,530 t is based on abundance estimates derived from an age-structured model developed with AD Model Builder software.  Similar to the previous assessment, the model accommodated a higher proportion of females in the larger size intervals of both survey and fishery data by giving males a higher mortality rate than females.  Exploitable biomass in 2001 is estimated to be greater than B_40% and ABC was determined to be 148,150 t based on Tier 3a calculations (F_40%= 0.134).  The overfishing level based on F_35%= 0.159 is estimated at 173,550 t.
  

GOA Atka Mackerel

Prior to 1997, exploitable biomass and ABC for Atka mackerel were based on triennial bottom trawl survey estimates.  However, schooling behavior, patchy distribution, and habitat preference makes this species difficult to sample with standard trawl survey gear.  Atka mackerel are also poor targets for hydroacoustic surveys because they lack swim bladders.  Reevaluation of historical survey data indicated abundance estimates prior to 1997 were also compromised by high variability.  Thus, existing GOA bottom trawl survey data has limited utility for either absolute abundance estimates or indices for Atka mackerel.  A bycatch-only fishery was recommended as a harvest policy for Atka mackerel because:  1) there is no reliable biomass estimate; 2) localized depletion may occur; and 3) this species has previously exhibited a particular vulnerability to fishing pressure in the GOA.  The ABC of 600 t in 2001 was determined to be sufficient to satisfy bycatch needs in other fisheries.  Under Tier 6 criteria, the overfishing level is equal to 6,200 t, the average catch for 1978-95.

By Anne Hollowed and Jim Ianelli.