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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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