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NOAA Technical Memorandum NMFS-AFSC-198

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Aleutian Islands cooperative acoustic survey study for 2006

Abstract

Results from the 2006 Aleutian Islands cooperative acoustic survey study (AICASS) conducted in March – April 2006 are presented. These surveys were part of a cooperative project between the National Marine Fisheries Service, the Aleut Enterprise Corporation, the owners and operators of the FV Muir Milach, and Adak Fisheries LLC to test the feasibility of using small (< 35 m) commercial fishing vessels to conduct acoustic surveys on walleye pollock (Theragra chalcogramma) in the central Aleutian Islands. To verify the acoustic data and to support the study, 1,000 metric tons (t) of walleye pollock was allocated to be harvested within Steller sea lion critical habitat. The acoustic and biological information from the study is used to assess: 1) if it is feasible to conduct acoustic surveys in the Aleutian Islands using commercial fishing vessels, 2) if the data collected are of sufficient quality for management purposes, and 3) if pollock aggregations in the Aleutian Islands during the winter are sufficiently spatially and temporally stable to allow for biologically reasonable management measures to be enacted.

Six acoustic surveys were successfully completed resulting in precise estimates of pollock biomass in the surveyed areas over time. The abundance trend was stable for the first two surveys, and then declined significantly during the final four surveys. During the study, 965 t of groundfish were harvested, 97% of the harvested groundfish were removed from a 72 square nautical mile area in the center of the study area and 85% of the harvest occurred in the final 11 days of the study. The change in biomass from earlier to later surveys is much larger than the fishing removals, indicating that significant movement of pollock from the study area occurred. Distribution and abundance of pollock, although dynamic in the overall survey area, did remain stable during the times when, and in the areas where there were lower densities of pollock and lower fishing effort during the survey. Further studies would be needed to evaluate the cause of the decline in the fished area. Two possible ways of capturing this information would be to: 1) expand the survey to encompass the full extent of the pollock movement, and 2) use an acoustic buoy to observe the behavior of pollock in relation to vessel noise and fishing removals.

The scientific objectives of the 2006 AICASS were achieved. The project also fostered an excellent working relationship among NMFS, the Aleut Enterprise Corporation, and the fishing industry. Local participation and stakeholder involvement enhances NMFS ability to provide responsible stewardship of this important marine resource. Future work should consider the expansion of this technique to survey more areas within the Aleutian Islands to determine the status of this stock within Steller sea lion critical habitat.


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