The goal of the Fishery Interaction Team’s (FIT) on-going tag release-recovery studies is to determine the efficacy of trawl exclusion zones (TEZs) as a management tool to protect critical habitat. Trawl Exlusion Zones 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 were released in the central and western 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 20,000 fish in the Western Aleutian Islands (Buldir Island, Western Aleutian Islands Seamounts, Agattu Island, and Ingenstrem Rock) as well as Seguam Pass in the Central Aleutian Islands. The primary objective of this cruise on the F/T Seafisher 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 (Figs. 1 and 2). Recovery of tagged fish is also being augmented by the fishery outside of trawl exclusion zones.
Figure 1. Location of tag recovery hauls (orange) and tag release locations (blue) at Seguam Pass (Area 541). Numbers on map indicate research strata.
Figure 2. Location of tag recovery hauls (orange) and tag release locations (blue) in the Western Aleutian Islands (area 543). Numbers on map indicate research strata.
The 2015 tag recovery effort onboard the chartered research vessel Seafisher is the second tag recovery cruise of the study. As with the initial Seafisher cruise in October 2014, the 2015 study was conducted both inside and outside of trawl exclusion zones (TEZs). In January 2015, the Western Aleutian Islands (Area 543) were opened to the Atka mackerel fishery for the first time since 2011; the fishery has provided another source of tag recovery in the open areas outside of the TEZs. At Seguam Pass (Area 541), the fishery has been, and will continue to, provide additional tag recovery outside of the TEZ.
During the 2015cruise, we conducted 132 total trawl hauls. We examined 1,016,127 Atka mackerel (790.62 t) for tags at Seguam Pass and 2,409,483 Atka mackerel (1,133.59 t) for tags in the Western Aleutian Islands. Figures 1 and 2 show the locations of tag recovery and release tows. We recovered 40 wild tags: 7 at Seguam Pass and 33 in the Western Aleutian Islands. We obtained sexed length frequencies from 12,368 fish and collected 1,070 samples of stomachs and otoliths. In approximately half of the stomach/otolith samples, we also collected gonads. In addition, we noted gross maturity stage for both sexes and male spawning coloration for every lengthed male Atka mackerel. Figure 3 compares the observed length frequencies from each cruise (May-June 2014, October 2014, and the summer 2015 cruise). In general, the largest Atka mackerel were found at study sites located near shore (Seguam Pass, Buldir, Kiska, and Agattu) while considerably smaller fish were found at the offshore seamounts (Tahoma Reef, Tahoma Seamount, Heck Canyon, and Walls Plateau).
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 1,641 specimens for these projects.
Figure 3. Size frequency distribution of Atka mackerel during the tag release cruise (May-June 2014) and the two tag recovery cruises (October 2014 and April-May 2015). The group “543 Nearshore” consists of Kiska, Buldir East, Buldir West, Ingenstrem Rock, and Agattu; the group “543 Offshore” consists of Tahoma Reef, Tahoma Seamount, Heck Canyon, and Walls Plateau.
