Status of Stocks and Multispecies Assessments Program -
Fisheries Interaction Team

Atka Mackerel Tagging Studies

Atka mackerel represent one of the largest groundfish biomasses in the Aleutian archipelago, with current estimates of exploitable biomass in excess of 500,000 tons.  They occur in dense aggregations in the Aleutian island passes and  prefer habitat with strong currents.  Atka mackerel have been observed at great densities and are extremely patchily distributed in space and time.

In order to prevent possible prey shortage for the Steller sea lions, the National Marine Fisheries Service (NMFS) established 20nm no trawl zones around six sea lion rookeries in the eastern Aleutians in 1991.  In 1998, further efforts were made to spread out fishing effort temporally as well as spatially.  Instead of one season per year for Atka mackerel, an A and a B season were mandated and more quota was assigned to be caught outside of critical habitat.  These restrictions affected the fishery severely and the question arose as to the efficacy of the no trawl zones and the impact of the fishery on Atka mackerel.  In order to measure the impact, it is necessary to estimate small scale Atka mackerel abundance and potential changes in behavior or movement of Atka mackerel that could be attributed to the fishery.  The goal of this project is to use tagging methods to estimate local abundance and small scale movement of Atka mackerel around Steller sea lion rookeries and to examine potential fishery effects on Atka mackerel movement and abundance. 

A feasibility study was conducted in 1999 at Seguam Pass.  In summer 2000, approximately 8000 tagged Atka mackerel were released in Seguam Pass, and in 2001 approximately 1000 were released during a truncated cruise.  In June-July 2002, ~ 21,000 fish were tagged in the Seguam Pass area, and ~ 14,520 were tagged near Tanaga Pass.   Recovery of tagged fish is supplied by the fishery in the open area outside the trawl exclusion zone.  Recoveries in the closed area are provided by chartered recovery cruises. 

The tagging model used was an integrated model using maximum likelihood to estimate all parameters simultaneously.  There were four components of the model including expected tag recoveries, tag loss, tag survival, and tag reporting.

Results to date suggest that there is relatively little movement of Atka mackerel from inside to outside the trawl exclusion zones, indicating that trawl exclusion zones are effective at protecting Atka mackerel near Steller sea lion rookeries around Seguam and Tanaga Passes.  Caution should be used in applying these results to other areas, each with resident Atka mackerel populations and fisheries of different size and distribution.  To examine geographical variation in movement and local abundance, FIT scientists will begin a parallel tag release-recovery study in third study area in the western Aleutians in 2003. 

Contact

For more details on the results summarized above, see the documents below or contact Susanne McDermott at susanne.mcdermott@noaa.gov or 1-206-526-4417