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Status of Stocks & Multispecies Assessment Program

Eastern Bering Sea Pollock Fishery

Research on aspects of the biology of walleye pollock and management implications continues to be actively pursued within the REFM Division. The issues facing fisheries management in Alaska are growing in complexity and pose new challenges. These issues include implementing practical regulations that satisfy a diverse set of biological, economic, and ecosystem objectives.

The largest fishery, walleye pollock in the eastern Bering Sea, enjoys a number of unique characteristics. Under the current regime, for example, two scientific observers are deployed on each vessel and extensive real-time reporting is required. The fact that this fishery is regulated to use only pelagic trawls (though bottom contact does occur) results in reduced bottom-habitat disturbance and reduced bycatch of nontarget species. Also, the fishery operates within strict catch limits by seasons and areas. The highest value from this fishery is derived from the production of prespawning roe. The rationalization of the fishery (whereby entry is limited and participating fishers are granted rights to a proportion of the annual quota) has further enhanced the value of the fishery since waste has declined.

From a biological perspective, the high level of observer coverage, combined with regular extensive surveys provides a unique situation to directly apply fisheries population dynamics theory into management. This provides the first tier of resource protection—that which avoids overfishing on a single-species basis.

figure 6, see caption
Figure 6.  Mean pollock body mass (kg) given length (cm) for the eastern Bering Sea stock by month based on NMFS fishery observer data, 1991-2006.

figure 7, see caption
Figure 7.  Scatter-plot results of simulation modeling of the present management strategy for eastern Bering Sea pollock showing how harvest rates change and when an upper limit of 1.5 million t TAC (pollock only) is imposed.

figure 8, see caption
Figure 8.  Normalized (to have mean value equal to one) estimates of pollock trawl effort (duration) and Chinook salmon bycatch, 1990-2007.

As an example of the applicability and extent of observer data, fine-scale patterns in growth (expressed as body weight for given lengths) reveal distinct monthly declines through the winter months followed by "fattest" conditions in September (Fig. 6). This type of information, also broken out by regions, provides signals that reflect changes in environmental conditions that affect how management recommendations are formulated.

The next tier of conservation considers the multi-species aspect of the fishery whereby any bycatch is recorded and counted against separate quota levels. Additionally, the annual overall multispecies limit of 2.0 million metric tons (t) for groundfish catch in this region impacts the levels of fishing mortalities for individual stocks.

Recent developments on management strategy evaluations for eastern Bering Sea pollock and yellowfin sole were presented at the February North Pacific Fishery Management Council meeting in Seattle. Results from this work show how management decisions for these stocks, given the overall constraint, are likely to play out under various productivity hypotheses (e.g., Fig. 7).

During periods of high pollock abundance levels, depending on the multispecies aspect of fisheries performance, the full 2.0 million t is nearly taken. During other years, in fisheries with higher levels of nontarget bycatch (e.g., flatfish fisheries), it is more difficult for the fleets to catch the 2.0 million t optimum yield (OY).

The levels of salmon bycatch in the eastern Bering Sea pollock fishery have increased in recent years, despite proactive management measures designed to reduce bycatch. Consequently, alternative management measures are being proposed and an environmental impact statement is currently under way.

The pollock stock in this region has dropped below the expected long-term average in 2008, and there was concern that increases in fishing effort may exacerbate bycatch. However, data on effort by the fleet show only a slight increase, whereas the Chinook salmon bycatch was nearly three times above average (Fig. 8).

The preliminary levels recorded for the first quarter of 2008 in this fishery appear to be back below mean levels. However, the new management measures (anticipated to be in place by late 2009) will add further restrictions on the pollock fishery, particularly in years where Chinook salmon abundance is high.

By James Ianelli


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