FIT Research Projects: 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 360,000 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.
Atka mackerel tag-recapture study locations
Biomass and movement rates were estimated with an integrated model (McDermott et al., 2005) that uses 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.
From 1999-2006, roughly 80,000 Atka mackerel have been tagged and released in our study areas at Seguam Pass, Tanaga Pass, Amchitka Island and Kiska Island of which 2152 have been recovered to date (Table 1 and 2).
Tag releases were conducted aboard the chartered Vessel Pacific Explorer and tag recoveries were conducted aboard the chartered Vessel
Seafisher. In addition, the Atka mackerel fishery provided a substantial amount of the tag recoveries in the areas open to fishing.
Tagging procedures and recovery sampling are described in detail in McDermott et al 2005. Since 2005 this study has been a cooperative venture with the non-profit organization North Pacific Fisheries Foundation which has funded a large part of the 2006 tag release and recovery field work.
Charter vessel CPUE was estimated from the hauls of the recovery cruise with the Chartered factory trawler Seafisher as the average Catch in tons per hour trawled. The vessel was using commercial fishing gear.
Preliminary results presented here are from the years 2000–2003 and will be updated for 2006 in the near future. Population sizes and biomass were highest at Seguam Pass and lowest at the south end of Amchitka Island and are summarized in Table 3 and Fig. 1, Fig. 2, and Fig. 3. In all areas, biomass inside the TEZs was similar to or greater than biomass outside the TEZs (Fig. 1). In all areas, movement rates from inside to outside were similar to or less than movement rates from outside to inside, with the exception of Amchitka Island where movement rates may have been greater from inside to outside. In addition, movement rates were greater overall at Amchitka Island than at any of the other study areas (Fig. 2). Population estimates for Amchitka Island north and Tanaga West were estimated for inside and outside the TEZ’s combined since the model could not estimate population size for the areas separately.
Vessel CPUE was highest at Seguam Pass and lowest at Amchitka (Fig. 3) and seemed to show the same trends as the population estimates. CPUE (tons of Atka mackerel caught per hour) only reflects the fish density in the sampled hauls. It does not take into account the differences in geographical size of the habitat. Therefore it seems reasonable that CPUE is about three times as high in Seguam as it is in Amchitka, even though population estimates are more than ten times as high. The geographical area of Atka mackerel trawlable habitat at Seguam pass is much larger than the one at Amchitka which is reflected in the larger population size.
These results suggest that TEZs in Seguam and Tanaga Passes, where Atka mackerel biomass is relatively high and movement is relatively low, may be effective at preserving local foraging areas for SSL. In contrast, the TEZ at the south end of Amchitka, where biomass is low compared to other areas and movement is high, may be less effective. These differences in movement relative to TEZs may be due to differences in the distribution of Atka mackerel habitat. For example, the boundaries of the TEZs at Seguam and Tanaga passes appear to coincide with natural Atka mackerel habitat boundaries (by chance). In contrast, the TEZs at Amchitka Island, appear to bisect Atka mackerel habitat. This may be why movement rates relative to TEZ boundaries at Amchitka were higher than at Seguam and Tanaga passes.
For more details on the results summarized above,
see the documents below or contact Susanne McDermott at firstname.lastname@example.org or 1-206-526-4417.
Research Reports and Activities
McDermott, S. F., Maslenkov, K. P., Gunderson, D. R. 2007. Annual fecundity, batch fecundity, and oocyte atresia of Atka mackerel (Pleurogrammus monopterygius) in Alaskan waters. Fish. Bull. 105: 19-29.
McDermott, S.F., L.W. Fritz, V. Haist. 2005. Estimating movement and abundance of Atka mackerel (Pleurogrammus monopterygius) with tag-release-recapture data.
Fish.Oceanogr. 14 (Suppl.1) 113-130.
F/T Seafisher Cruise 200701 (PDF)
October 9 – 25, 2007. Project Title: Atka Mackerel Tag Recovery Kiska Island and Seguam Pass, Aleutian Islands Alaska
F/T Seafisher Cruise 200601(PDF)
October 11 – November 1, 2006. Project Title: Atka Mackerel Tag Recovery Kiska Island and Seguam Pass, Aleutian Islands Alaska
F/V Pacific Explorer Cruise 200601
July 8 - July 21, 2006. Project Title: Atka mackerel tag and release, Kiska and Seguam Islands, Aleutian Islands, Alaska
AFSC Quarterly Report
Atka Mackerel Tagging
F/T Seafisher Cruise, SE200301
(PDF) October 5 - 31, 2003. Project Title: Atka mackerel tag recovery Amchitka Island and Seguam Pass, Aleutian Islands Alaska
F/V Pacific Explorer Cruise 200301
July 12-26, 2003. Project Title: Atka mackerel tag and release Amchitka Island area, Aleutian Islands Alaska
F/T Seafisher Cruises SE200201, SE200202 (PDF) August 23-28, 2002 and September 30 - October 12, 2002. Project
Title: Atka mackerel tag recovery Seguam and Tanaga Passes, Aleutian
F/V Pacific Explorer Cruise 200201
(PDF) June 10 - July 9, 2002. Project Title: Atka mackerel tag and release Seguam and Tanaga Passes, Aleutian Islands Alaska.
AFSC Quarterly Report
The Fishery Interaction Team: Investigating the
potential impacts of commercial fishing on the foraging success of
endangered Steller sea lions.
K. Rand and S. McDermott.
Seasonal changes in Atka
mackerel sex ratios in Seguam and Tanaga Passes during 2002
(PowerPoint). Marine Science for the Northeast Pacific: Science
for resource-dependent communities, January 13-17, 2003, Anchorage