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Salmon Excluder Testing in the Gulf of Alaska Shows Promising Results

Aug 21, 2013
Summer 2013

Early this spring GMRI collaborated with the North Pacific Fisheries Research Foundation to test a salmon excluder device for use in the Alaskan pollock midwater trawl fishery. Recent bycatch limits on salmon, set by the North Pacific Fishery Management Council in June 2011 (Amendment 93 to Alaska Groundfish FMP) prompted the study as a way to help pollock vessels remain within the new 25,000-fish, fleet-wide annual harvest limit for Chinook salmon. The new limit for the central and western Gulf of Alaska pollock fisheries has created some concern, as it is shared among the fleet -- so the bycatch of one boat affects everyone. The limit set by the Council is close to the average catch history since 2003, but the more recent years have seen some higher catches (44,061 fish in 2010 for example). 

The design of the salmon excluder was inspired by previous work on salmon bycatch reduction in the Bering Sea pollock fishery. It creates selectivity of the two fish species by exploiting the salmon's superior swimming ability to move up and out of an escape opening, while the slower pollock are retained in the net. This design showed great success in the Bering Sea, where many boats continue to use the excluder. Adaptations of the design for use by the smaller Gulf of Alaska boats include a scaled down net size, altered water flow regime, lower vessel horsepower and tow speeds, and variable fish densities.

Initial sea trials out of Kodiak, Alaska in April 2013, showed salmon escapement rates of over 20% and pollock retention rates as high as 99%, and there is hope for further improvement on these initially promising results. Researchers are continuing to work with captains to test the excluder under conditions truly representative of commercial fishing operations. They are looking for situations with a relatively high number of salmon and enough pollock to fully vet the results. Future sea trials are planned for the fall as well as the spring and fall of 2014. After seeing the success of the Bering Sea excluder, industry members are eager to see the project results. Potential economic impacts associated with a fishery shutdown would be significant and far reaching. The Alaskan pollock fishery lands almost 3 billion pounds of fish per year -- the largest fishery in the U.S. by weight -- valued at just under $375 million.