Science



Science

Stock Assessments

Annual Bottom Trawl Survey

Each year since 1975, the Alaska Fisheries Science Center (AFSC) conducts an eastern Bering Sea bottom trawl survey. The purpose of this survey is to collect data on the distribution and abundance of crab, groundfish, and other benthic resources in the eastern Bering Sea. These fishery-independent data are used to estimate population abundances for the management of commercially important species in the region. This annual survey and data collection are essential for proper assessment and management of target stocks and non-target species. Without the bottom trawl survey and associated collection of data, there would be: 1) a decrease in the precision of biomass estimates resulting in increased uncertainty regarding population dynamics; 2) increased annual variation in catch limit recommendations resulting in a higher risk of overfishing; 3) a loss of other important biological information including age, growth, and spatial distribution; and 4) foregone economic opportunities as a result of an increase in precautionary management. An interactive data map showing the eastern Bering Sea shelf bottom trawl survey catch per unit effort for commercially important crab species from 1975 to the present can be found at http://www.afsc.noaa.gov/maps/crabmap/crabmap.html.

Crab Plan Team and Scientific and Statistical Committee

Data collected from the annual eastern Bering Sea bottom trawl survey (combined with other data sources like observer and fishery-dependent information) make it possible for stock assessment scientists to build detailed population dynamics models for each of the harvested crab species. These models are used to provide biologically-based quota recommendations that ensure commercial fishing remains at a level to sustain the population over the long-term.

An annual stock assessment and fishery evaluation (SAFE) report is prepared that provides the current biological, ecosystem, and economic data associated with each target crab species. The Crab Plan Team (CPT) and Scientific and Statistical Committee (SSC) review each assessment and modeling data and make recommendations for biological reference points for each of the stocks. The CPT and SSC are composed of leading scientists in biology, economics, statistics, and social science and are made up of individuals from the Alaska Fisheries Science Center (AFSC), Alaska Department of Fish and Game (ADF&G), University of Alaska Fairbanks (UAF), University of Washington (UW), and the NMFS Alaska Regional Office (AKRO). The purpose of the review is to assess the scientific validity of the stock assessment, including any assumptions, methods, results and conclusions. Specific aspects of the review will vary, but may include: quality of the data collected or used for the assessment, appropriateness of the analyses, validity of the results and conclusions, and appropriateness of the scope of the assessment (e.g., were all relevant data and information considered). The primary function of both the CPT and SSC is to provide the North Pacific Fishery Management Council (Council) with the best available scientific information, including scientifically based recommendations regarding appropriate harvest levels and measures for the conservation and management of the Bering Sea and Aleutian Islands (BSAI) king and Tanner crab fisheries. All recommendations must be designed to prevent overfishing while achieving optimum yield (National Standard 1). All recommendations must also be scientifically based (National Standard 2), drawing upon the CPT's and SSC's expertise is the areas of regulatory management, natural and social science, mathematics and statistics. The annual BSAI King and Tanner Crab SAFE report provides the Council with a summary of the most recent biological condition of the crab stocks and the social and economic condition of the fishing and processing industries. The SAFE report summarizes the best available scientific information concerning the past, present and possible future condition of the crab stocks and fisheries, along with ecosystem concerns. Because the Council strives to use the best available scientific and commercial data and analyses when making regulatory decisions, scientific peer review is an integral component of the process for ensuring the quality and integrity of the scientific assessments that are used to determine biologically acceptable catch limits for each of the commercially harvested crab species. More information on the Crab Plan Team and the SSC can be found on the North Pacific Council's website at http://www.npfmc.org/fishery-management-plan-team/bsai-crab-plan-team/ and http://www.npfmc.org/scientific-and-statistical-committee/. Links to the most recent King and Tanner crab SAFE Reports can be found at http://www.npfmc.org/safe-stock-assessment-and-fishery-evaluation-reports/.

Tier System

As part of the annual stock assessment review process, status determination criteria for commercial crab stocks are annually calculated using a five-tier system that accommodates varying levels of uncertainty of information. This tier system allows the incorporation of new scientific information and provides the ability to improve status determination criteria as new information becomes available. Under this system, overfishing and overfished criteria and acceptable biological catch (ABC) levels are formulated annually. For crab stocks, the annual catch limit (ACL) is equal to the ABC. For crab stocks, the overfishing limit (OFL) equals maximum sustainable yield (MSY) for that stock. Each crab stock is annually assessed to determine its status and whether: 1) overfishing is occurring; 2) the stock is overfished or approaching an overfished condition; and 3) the catch (all directed and non-directed fishery removals including retained and discards) has exceeded the ACL. For Tiers 1 through 3, reliable estimates of biomass, biomass at MSY, the fishing rate necessary to achieve MSY, and other essential life-history information are available. Tier 4 is for stocks where essential life history and other information are insufficient to achieve Tier 3. Tier 5 stocks have no reliable estimates of biomass and only historical catch data is available. A more detailed description of the status determination criteria and the five-tier system can be found in the federal King and Tanner Crab Fishery Management Plan at http://www.npfmc.org/wp-content/PDFdocuments/fmp/CrabFMPOct11.pdf.

Uncertainty

In setting annual total allowable catch levels (TACs), the Alaska Department of Fish and Game (ADF&G) takes the following factors into consideration: 1) whether the ACL for a stock was exceeded in the previous year; 2) stock status relative to the OFL and ABC; 3) estimates of exploitable biomass; 4) estimates of recruitment; 5) estimates of thresholds; 6) market and other economic considerations; 7) any additional factors pertaining to the health and status of the stock; and 8) additional uncertainty. Additional uncertainty includes both management uncertainty and scientific uncertainty. Management uncertainty encompasses the uncertainty in the ability of managers to constrain catch such that the ACL is not exceeded and the ability to quantify the true catch amount from all sources. Scientific uncertainty that is not already accounted for in the ABC including uncertainty in bycatch mortality, estimates and trends in size composition, shell condition, molt status, reproductive condition, spatial distribution as well as environmental conditions, fishery performance, and fleet behavior. ADF&G establishes the annual TAC for each crab stock at a level sufficiently below the ACL to ensure that the sum of the catch and assessment of additional uncertainty do not exceed an ACL. More information on the dual management system for commercial crab stock as well as on the incorporation of uncertainty into the TAC-setting process can be found in the King and Tanner Crab Fishery Management Plan at http://www.npfmc.org/wp-content/PDFdocuments/fmp/CrabFMPOct11.pdf.

ABSC Science Symposiums

Every year in September, in conjunction with the fall Crab Plan Team meeting, ABSC hosts a Crab Science Symposium for its members and all other interested stakeholders and members of the public. Crab scientists, researchers, and managers are invited to provide presentations and answer questions on the latest science and relevant topics to Bering Sea crab harvesters. Past Symposiums include regular presentations on and preliminary results from the NMFS bottom trawl survey. They have also included presentations on such topics as: the size-fecundity relationship in Bristol Bay red king crab; the life cycle of the male snow crab; results from handling mortality experiments for snow crab; ocean acidification and impacts to Bristol Bay red king crab; hatchery production of red and blue king crab; and predation and habitat use of red king crab around Kodiak Island.

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Science

Research

Bering Sea Fisheries Research Foundation

The Bering Sea Fisheries Research Foundation (BSFRF) is a non-profit research foundation voluntarily funded by both the crab harvesting and processing sectors as well as by fishery-dependent communities (http://www.bsfrf.org/). The BSFRF provides a forum for industry members, fisheries managers, and scientists to interact and work cooperatively in order to conduct scientific research that is specifically designed to expand the knowledge base for commercial Bering Sea crab stocks. Expanding and supplementing the available information on harvested crab species allows for improved sustainability and management of crab resources in the Bering Sea.

Research projects conducted through the BSFRF are integrated collaborative efforts and the scope of research and array of scientific partners has continued to grow each year. Extensive cooperation on research priorities, project design, planning, methodology, field research, analyses, and reporting are coordinated among multiple partners including researchers and managers from the National Marine Fisheries Service (NMFS), the Alaska Department of Fish and Game (ADF&G), the University of Washington, the University of Alaska Fairbanks, the Department of Fisheries and Oceans Canada (DFO). The ultimate goal of the research projects undertaken is to assist in both determining and developing the best scientific approach for gathering and producing information (through improved stock assessments) for effective and sustainable management of the Bering Sea crab fisheries. Better research results in better management thereby ensuring the fisheries will be protected and preserved while simultaneously producing long-term sustainable yields.

Recently, the BSFRF was instrumental in coordinating the necessary research and data collection that allowed for a reduction in the snow crab handling mortality estimate used in the snow crab stock assessment model. In the eastern Bering Sea snow crab fishery, the discarded catch of snow crab (primarily small males) is approximately one-third of the total catch. Prior to 2013, the estimated mortality rate for this discarded catch was 50%, which was not based on any previous data or studies. The BSFRF was able to specifically hire and train fisheries observers to collect snow crab mortality data using a scientifically-validated approach based on a suite of reflex responses of crab captured during the fishery. From this work, the Crab Plan Team and Science and Statistical Committee revised the snow crab handling mortality estimate down to 30%. With all other aspects of the snow crab stock assessment model being equal, this change in estimated handling mortality resulted in an approximate 13% difference (increase) in the resulting acceptable biological catch (ABC) for snow crab.

Some of the other ongoing and past research projects conducted through the BSFRF include:

2011/2012 Bristol Bay Red King Crab Inshore Survey: Due to uncertainties regarding the distribution and abundance of red king crab inshore, the main goal of this research project is to improve understanding of the distribution of male and female red king crab outside of and near the edge of the standard AFSC eastern Bering Sea bottom trawl survey area in Bristol Bay.

2011 Snow Crab Growth Study: The main goals of this work were to collect pre-molt juvenile snow crab during the spring (when molting is known to occur), to transport the snow crab from the molting areas on the northwest Bering Sea shelf to holding facilities both at Dutch Harbor and at the Alaska Fisheries Science Center Kodiak laboratory, and to maintain the snow crab until molting occurred. The data from this experiment resulted in a prediction of post-molt carapace width from pre-molt carapace width, which was then used in the snow crab stock assessment model to improve the estimation of snow crab growth per molt within the model.

2010 Snow Crab Tagging: This research continued tagging and movement efforts, which started with red king crab, to understand adult male snow crab seasonal movements in the Bering Sea using archival tags.

2009/10 Eastern Bering Sea Tanner Crab Size Limit: This research focused on analysis of the minimum size limit(s) for eastern Bering Sea Tanner crab fisheries. The goal of this work was to evaluate the merits of a reduced minimum size limit(s) for the Tanner crab fisheries in the eastern Bering Sea. A number of important research questions were addressed as part of this work, including: the size of maturity of Tanner crab and how it has changed over time; the optimal size limit based on yield per recruit; the degree to which commercial landings, bycatch and discard amounts, and revenues change under a reduced size limit at varying levels of abundance; and how harvest rates should be modified under alternative minimum size limits.

Alaska King Crab Research, Rehabilitation, and Biology Program

Formed in 2004, the Alaska King Crab Research, Rehabilitation and Biology (AKCRRAB) Program is an Alaska Sea Grant partnership with regional fishermen's groups, coastal communities, the National Marine Fisheries Service (NMFS), the Alutiiq Pride Shellfish Hatchery and Chugach Regional Resources Commission, and the University of Alaska Fairbanks (UAF) School of Fisheries and Ocean Sciences (http://seagrant.uaf.edu/research/projects/initiatives/king-crab/general/index.php). AKCRRAB was initiated to conduct a research program aimed at hatching and rearing wild red and blue king crabs in a large-scale hatchery setting. The mission of the program is to understand the large-scale culturing needs of wild red and blue king crab stocks, and to perfect strategies for hatching and rearing king crab to a stage where they can be released into the wild and contribute to reversing low wild stock abundance in Alaska. The ultimate goals of the program are to add to the scientific understanding of king crab life history and ecology and to rehabilitate depressed king crab populations throughout Alaska. The coalition of state, federal, and stakeholder groups views the efforts of the AKCRRAB program as important to the region's long-term economic development and sustainability.

Every year since 2007, king crab broodstock have been collected under permits provided by the Alaska Department of Fish and Game. The Alutiiq Pride Shellfish Hatchery and UAF Seward Marine Center house and care for the adult broodstock and offspring. Hundreds of thousands of eggs from female king crab hatch in early spring, and the swimming larvae settle to become juveniles approximately two months later. AKCRRAB's team of production biologists, scientists, and graduate students has made great progress towards advancing the science and technology necessary to support hatchery production of juvenile king crab. Production biologists have achieved high survival rates for king crab (31% in 2013) and scientists and graduate students have conducted research on larval nutrition, rearing densities, and rearing temperatures. Work has also been done on juvenile crab nutrition, release strategies, substrate preference, and the development of genetic markers. Scientists involved in AKCRRAB research highlight their work each month in a newsletter called AKCRRAB News Flash, which can be found at http://seagrant.uaf.edu/research/projects/initiatives/king-crab/newsflash/index.php.

North Pacific Research Board

The North Pacific Research Board (NPRB) was created by Congress in 1997 to recommend marine research activities to the US Secretary of Commerce, supported by interest earned from the Environmental Improvement and Restoration Fund. The enabling legislation requires the funds to be used to conduct research on or relating to the fisheries or marine ecosystems in the North Pacific Ocean, Bering Sea, and Arctic Ocean (http://www.nprb.org/). To achieve its overall mission of building a clear understanding of North Pacific ecosystems, the NPRB must emphasize research designed to address pressing fishery management issues or marine ecosystem information needs and supports wide-ranging peer-reviewed scientific research in the Gulf of Alaska, Bering Sea, Aleutian Islands and Arctic Ocean to inform effective management and sustainable use of marine resources.

The Board is comprised of twenty members representing federal, state and other entities. The board receives advice from both an Advisory Panel and a Science Panel. The Board's recommendations on research proposals are subject to approval by the U.S. Secretary of Commerce, whose authority is delegated to the Alaska Regional Administrator for the National Marine Fisheries Service (NMFS). The Board relies upon input from external reviewers in addition to its science and advisory panels to fund the most meritorious science projects that address pressing fishery management and ecosystem information needs. Proposals are selected for funding through the annual research program or the long-term monitoring program. The NPRB also develops and implements multi-institution, interdisciplinary science projects under the integrated ecosystem research program to create a more integrated understanding of Alaska's ocean ecosystems. Additionally, NPRB administers a graduate student research award program that encourages students to pursue scientific and scholarly research that addresses management issues in northern seas.

To date, the NPRB has funded a total of 351 projects for a total of over $58 million awarded thorough its Annual Research Program (http://www.nprb.org/annual-research-program/about-the-program/). Projects touch on all aspects of Alaska's marine ecosystems. Since the development of the NPRB Science Plan in 2005, the annual Request for Proposals (RFPs) have been structured around specific research themes that address both pressing fishery management needs and marine ecosystem information needs. The full NPRB Science Plan can be found at http://www.nprb.org/assets/images/uploads/science_plan_nov05_low.pdf. Past, crab-specific, projects funded through NPRB include:

Essential Habitat for Pribilof Island Blue King Crab

Female Reproductive Output of Snow Crab in the Eastern Bering Sea

Retrospective Analysis of Kodiak Red King Crab

Quantification of Unobserved Injury and Mortality of Bering Sea Crabs Due to Encounters with Trawls on the Seafloor

Reduction of Bycatch Mortality for Non-target Crab Species in the Commercial Snow Crab Fishery

Evaluating Methods for Determining Overfishing Levels for Bering-Sea Aleutian Islands Crab Stocks

Mapping Tanner Crab Habitat in the Kodiak Area of the Gulf of Alaska

Development of Biochemical Measures of Age in the Alaskan Red King Crab: Validation, Refinement, and Initial Assessment

Research Priorities

As part of its regular duties, the North Pacific Fishery Management Council identifies priorities for research (with input provided by Plan Teams, the Scientific and Statistical Committee, and the Advisory Panel) as those activities that are the most important for the conservation and management of fisheries in the Gulf of Alaska, Aleutian Islands, eastern Bering Sea, and the Arctic. This listing of priorities serves two purposes: 1) to meet the requirements of the revised Magnuson-Stevens Fishery and Conservation Management Act (MSA) for all eight regional Councils to identify research that is needed in the next one to five years; and 2) to provide guidance and recommendations on research priorities to the broader research community and funding agencies. Research priorities are organized into four categories: critical, high, medium, and low.

The list of the Council's research priorities can be found at https://research.psmfc.org. Some of the crab-specific research items identified by the Council as having a high priority include:

Life History Research on Non-recovering Crab Stocks

Spatial Distribution of Male Snow Crab

Improve Handling Mortality Rate Estimates for Crab

Studies to Identify Crab Stock Boundaries

Effects of Trawling on Female Red King Crab and Subsequent Recruitment

Studies on Factors that Affect Catchability Particularly for King and Tanner Crab

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Science

Stock Rebuilding

Snow Crab

The National Marine Fisheries Service (NMFS) declared the Bering Sea snow crab stock overfished in 1999 because the spawning stock biomass estimated from the bottom trawl survey was below the minimum threshold specified in the Fishery Management Plan (FMP). As required by the Magnuson-Stevens Fishery and Conservation Management Act, the North Pacific Fishery Management Council (Council) developed and implemented a rebuilding plan within one year of this declaration. This framework rebuilding plan contained three components: 1) a harvest strategy; 2) bycatch control measures; and 3) habitat protection measures. Because the FMP defers management to the State of Alaska, with oversight by NMFS and the Council, it was the authority of the Alaska Department of Fish and Game (ADF&G) to develop appropriate harvest strategies (which allowed the fishery to continue during the rebuilding period) to increase spawning biomass as more large male crab are conserved and gear modification measures to reduce bycatch of females and sublegal sized males in the directed fishery.

During the ten year rebuilding timeframe, the currency for estimating snow crab biomass at the level for maximum sustainable yield (BMSY) changed from that previously based on total mature (morphometrically mature males and females) survey biomass to that currently based on the model estimated mature male biomass (MMB) at time of mating. The structure of the stock assessment model also changed during this time. The snow crab stock is considered "rebuilt" when the stock size reaches BMSY in one year. Using the current definitions for estimating BMSY, MMB at mating was above the proxy threshold in 2010/11 and the stock was declared rebuilt in 2011.

Tanner Crab

The National Marine Fisheries Service (NMFS) declared the Bering Sea Tanner crab stock overfished in 1999 because the spawning stock biomass estimated from the bottom trawl survey was below the minimum threshold specified in the Fishery Management Plan (FMP). As required by the Magnuson-Stevens Fishery and Conservation Management Act, the North Pacific Fishery Management Council (Council) developed and implemented a rebuilding plan within one year of this declaration. This framework rebuilding plan contained three components: 1) a harvest strategy; 2) bycatch control measures; and 3) habitat protection measures. Because the FMP defers management to the State of Alaska, with oversight by NMFS and the Council, it was the authority of the Alaska Department of Fish and Game (ADF&G) to develop appropriate harvest strategies to increase spawning biomass as more large male crab are conserved and gear modification measures to reduce bycatch of females and sublegal sized males in the directed fishery. Unlike snow crab, the Tanner crab fishery was only opened a few seasons (2005-2009) during its rebuilding timeframe.

During 2011 and 2012, extensive work was done by the stock assessment author, Crab Plan Team members, and the Science and Statistical Committee to revise the Tanner crab model for its improved suitability in the stock assessment and rebuilding analysis. In May 2012 the Crab Plan recommended that the revised and updated model be used for all future Tanner crab stock assessments and in June 2012 the SSC reviewed the model and accepted the CPT's recommendations. Based on the newly-accepted assessment model, in October 2012 the SSC elevated the Tanner crab stock from Tier 4 to Tier 3 for status determination and for determining the overfishing limit (OFL) and acceptable biological catch (ABC) level. The change from Tier 4 to Tier 3 resulted in a large reduction in the estimate of biomass at the level for maximum sustainable yield (BMSY) used for status determination Based upon these results from the newly-accepted assessment model, the Tanner crab stock was subsequently declared rebuilt and not overfished. Although the Tanner crab stock was declared rebuilt in 2012, ADF&G did not open the directed commercial fishery for Tanner crab until the 2013/2014 season based on specific parameters contained in their harvest strategy.

St. Matthew Blue King Crab

The National Marine Fisheries Service (NMFS) declared the St. Matthew blue king crab stock overfished in 1999 because the spawning stock biomass estimated from the bottom trawl survey was below the minimum threshold specified in the Fishery Management Plan (FMP). As required by the Magnuson-Stevens Fishery and Conservation Management Act, the North Pacific Fishery Management Council (Council) developed and implemented a rebuilding plan within one year of this declaration. This framework rebuilding plan contained three components: 1) a harvest strategy; 2) bycatch control measures; and 3) habitat protection measures. Because the FMP defers management to the State of Alaska, with oversight by NMFS and the Council, it was the authority of the Alaska Department of Fish and Game (ADF&G) to develop appropriate harvest strategies to increase spawning biomass as more large male crab are conserved and gear modification measures to reduce bycatch of females and sublegal sized males in the directed fishery. The ADF&G rebuilding harvest strategy closed the fishery until the stock was considering “rebuilt” (when the stock reaches a biomass level considered for maximum sustainable yield for two consecutive years).

In addition to the annual Bering Sea bottom trawl survey for monitoring the effectiveness of the rebuilding plan, ADF&G also conducts a pot survey on a triennial basis for blue king crab in the St. Matthew area. Most of the pot survey effort is devoted to the area south of St. Matthew Island in the relatively shallow waters (25-55 fathoms) that supports much of the blue king crab commercial fishery and the mature female population. Use of pots allows for surveying areas that are not accessible to the NMFS trawl survey. This survey is invaluable for providing population indices and indicators of crab distribution for large portions of the legal-sized male and mature female stock that are not represented in the annual NMFS trawl survey. After a ten year closure period, NMFS declared the St. Matthew blue king crab stock rebuilt in 2009 and the fishery was reopened. However, based on specific parameters contained in the ADF&G harvest strategy, the St. Matthew blue king crab commercial fishery was closed for the 2013/2014 season.

Pribilof Islands Blue King Crab

The National Marine Fisheries Service (NMFS) declared the Pribilof Island blue king crab stock overfished in 2002 because the spawning stock biomass estimated from the bottom trawl survey was below the minimum threshold specified in the Fishery Management Plan (FMP). As required by the Magnuson-Stevens Act, the North Pacific Fishery Management Council (Council) developed a rebuilding plan within one year of this declaration. Unlike the rebuilding plans for Tanner crab and snow crab, the rebuilding plan for Pribilof Islands blue king crab contains only a conservative harvest strategy to improve the status of the stock. Because the FMP defers management to the State of Alaska, with oversight by NMFS and the Council, under the authority of the Alaska Department of Fish and Game (ADF&G), the rebuilding harvest strategy closes the fishery until the stock is considering “rebuilt” (when the stock reaches a biomass level considered for maximum sustainable yield for two consecutive years).

At the time the original rebuilding plan was approved in 2003, no additional habitat or bycatch measures were included because neither was expected to have a measureable impact in rebuilding. Habitat was protected from fishing impacts due to trawl gear by the Pribilof Islands Habitat Conservation Zone, which encompasses the majority of blue king crab habitat, and bycatch in both the directed crab and groundfish fisheries was considered a negligible proportion of the total population abundance. However, recognizing that the original rebuilding plan had not achieved adequate progress towards rebuilding the stock by 2014 (ten-year timeframe from implementation), the Council took further action in 2012 to further limit groundfish fisheries near the Pribilof Islands. Because recent trends in crab bycatch had the potential to exceed the annual overfishing limit and acceptable biological catch for this stock, the Council took action to apply the Pribilof Islands Habitat Conservation Zone to those groundfish fisheries targeting Pacific cod with pot gear. The analyses that helped to inform and guide the Council's action on this issue can be found at http://www.npfmc.org/wp-content/PDFdocuments/catch_shares/Crab/PIBKCrebuildingEA512.pdf and http://www.npfmc.org/wp-content/PDFdocuments/catch_shares/Crab/PIBKCrebuildingAPX_512.pdf and

http://www.npfmc.org/wp-content/PDFdocuments/catch_shares/Crab/PIBKCrebuildingRIR512.pdf.

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Ocean Acidification

Ocean acidification is a decrease in the pH (increased acidity) of marine waters associated with rising carbon dioxide concentrations in seawater. Calcifying organisms, including crustaceans, are particularly vulnerable to this increase in carbon dioxide and changing ocean chemistry because a lower pH causes an increase in the dissolution rates of calcium carbonate. Calcium carbonate is essential component of the calcification process for crab species whereby their shells harden after molting. In other words, the more acidic the sea, the harder crab species have to work expending energy to build and maintain their exoskeletons. In addition, embryos and larvae exposed to increased acidity in seawater exhibit lower survival rates, lower growth rates, and increased rates of malformation.

King and Tanner crab experimental studies have been conducted by leading scientists and researchers at the Alaska Fisheries Science Center's Kodiak Laboratory (http://www.afsc.noaa.gov/kodiak/). The effects of increased carbon dioxide on the survival, condition, and growth of king and Tanner crab species were investigated from 2009 to 2011. At that same time, infrastructure was developed to support a multi-year program capable of assessing both direct and indirect effects of ocean acidification on shell building in commercial crab species in Alaska. The results of this research program will not only provide empirical data specific to the physiological response of crabs to increasingly acidic condition, but they will also support modeling efforts on the indirect impacts of ocean acidification associated with food webs and fisheries interactions. More information on this research into the effects of ocean acidification on Alaska marine resources can be found at http://www.afsc.noaa.gov/Quarterly/jas2012/JAS12-Feature2.pdf.

The issue of ocean acidification and its effects upon living marine resources and dependent-industries is gaining increased publicity and attention, including this recent multi-part Seattle Times article http://apps.seattletimes.com/reports/sea-change/2013/sep/11/pacific-ocean-perilous-turn-overview/. More information on the broader topic of ocean acidification, including research and monitoring investments that will improve our understanding of ocean acidification, its potential impacts on marine species and ecosystems, and adaptation and mitigation strategies can be found at http://oceanacidification.noaa.gov/IWGOA.aspx.

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Gear Interactions and Modifications

The potential for both bycatch and unobserved mortality of crabs that encounter bottom trawls but are not captured have long been a concern to directed crab harvesters and managers of crab and groundfish fisheries. The current suite of management measures to control and reduce crab bycatch in Alaska groundfish fisheries includes closure areas and species-specific crab bycatch limits. However, bycatch is only one source of mortality from directed groundfish fisheries; of greater concern is the unaccounted for mortality from direct trawl gear interactions as they occur at or near the seafloor.

Addressing and mitigating the issue of unobserved mortality has been done through experiments designed to assess the mortality probabilities for crabs that pass under the various components (sweeps, wings, and central footrope) of trawl gear and aimed at modifying bottom trawl gear to lessen such probabilities. Cooperative research undertaken by scientists with the Alaska Fisheries Science Center and members of the groundfish fleet (through Groundfish Forum), with the majority of funding provided through the North Pacific Research Board (NPRB), has resulted in the groundfish fleet voluntarily modifying their bottom trawl gear to use 24-inch bobbins (versus previously used 16-inch) bobbins as a way of reducing snow and Tanner crab mortality. More information on this work can be found on the NPRB website at:

http://www.nprb.org/.

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