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Status of Stocks & Multispecies Assessment Program

FIT Staff Conducts Successful Atka Mackerel Tag Recovery Cruise in the Aleutian Islands

Research Reports
Fall 2014
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Figure 1. Location of tag recovery hauls (blue) and tag release locations (red) near Seguam Pass (Area 541).  Numbers on map indicate research strata.

The goal of the Fishery Interaction Team's (FIT) ongoing tag-release-recovery studies is to determine the efficacy of trawl exclusion zones (TEZs) as a management tool to protect critical habitat. TEZs have been established around Steller sea lion rookeries to protect sea lion habitat and prey resources, including local populations of prey such as Atka mackerel.  Localized fishing may affect Atka mackerel abundance and distribution near sea lion rookeries.  Our tagging experiments estimate local abundance and movement between areas open and closed to the Atka mackerel fishery.  From 1999 through 2014, a total of approximately 130,000 tagged Atka mackerel have been released in the Aleutian Islands.  To date, over 3,000 tagged Atka mackerel have been recovered.  These data have contributed greatly to our understanding of small-scale movements and distributions of Atka mackerel around sea lion rookeries.  

In May and June 2014, a cooperative venture between the North Pacific Fisheries Foundation and NMFS tagged and released approximately 21,000 fish in the western Aleutian Islands (Buldir Island, WAI Seamounts, Agattu Island, and Ingenstrem Rock) as well as Seguam Pass in the Central Aleutian Islands (Figs. 1-2).  The primary objective of the factory trawler Seafisher Atka mackerel tag recovery cruise was to recover these tagged fish both in areas open to the Atka mackerel fishery and within trawl exclusion zones that are closed to the fishery.  Recovery of tagged fish is also being augmented by the fishery outside of trawl exclusion zones.

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Figure 2. Location of tag recovery hauls (blue) and tag release locations (red) in the Western Aleutian Islands (area 543). Numbers on map indicate research strata.

Secondary objectives included conducting undersea camera tows near fishing locations. These tows aided in the development of cameras as a tool for identifying fish habit as well as estimating fish species composition, density, and size.  In addition, Atka mackerel biological data including stomach samples, gonad samples, and age structures were collected during nearly every haul.

During this cruise we conducted 94 hauls and examined 1,934 t of Atka mackerel for tags (approximately 3.2 million individual fish).  We recovered 54 wild tags: 6 at Seguam pass and 48 in the Western Aleutian Islands. All of these tags were released during the 2014 tag release charter and all hauls were sampled for species composition.  In addition, we collected 737 Atka mackerel biological samples including stomach, gonad, and age structures, and we obtained sexed length frequencies from 8,776 individual fish.  Length distribution of Atka mackerel differed by area, with the small-sized fish found at the Western Aleutian sea mounts, medium-sized fish found at Buildir, Ingenstrem rock and Agattu, and the largest fish found at Seguam Pass (Fig. 3).

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Figure 3:  Length Frequency distribution in each study area. “WAI Nearshore” includes Buldir, Ingenstrem rock, and Aggatu; “WAI Seamounts” includes Tahoma Reef, Tahoma Seamount, Heck Canyon, and Walls Plateau.

In order to examine the habitat and develop indices of abundance, we conducted 22 underwater tows with a portable underwater camera (Figs. 4 and 5) using a stereo camera system developed at the AFSC by the Midwater Assessment and Conservation Engineering  group.

The data we collected on this cruise will be used to estimate population sizes of Atka mackerel in the study areas, as well as to understand relative abundance of other SSL prey species and invertebrates and the habitat types associated with those populations.

Finally, we conducted four special projects at the request of other researchers: stomach collections from the predominant fish species encountered, stable isotope samples from a range of fish species for Steller Sea lion dietary and mercury content analysis, rockfish maturity samples, and Pacific cod maturity samples. We collected an additional 752 specimens for these projects.

 

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Figure 4. Underwater stereo drop- camera system. Photo credit: Susanne McDermott, NOAA.
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Figure 5. Example of undersea camera footage. Photo credit: Mike Levine, NOAA.

 

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