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Status of Stocks & Multispecies Assessment Program

Atka Mackerel Tag Recovery Cruise 2006 in the Aleutian Islands

The Fishery Interaction Team (FIT) conducted an Atka mackerel tag recovery cruise in the Seguam pass and Kiska Island areas of the Aleutian Islands, Alaska. The first objective of our tag release-recovery study is to determine the efficacy of trawl exclusion zones as a management tool to maintain prey abundance/availability for Steller sea lions at local scales. Trawl exclusion zones were established around sea lion rookeries as a precautionary measure to protect critical sea lion habitat, including local populations of prey such as Atka mackerel. Localized fishing may affect Atka mackerel abundance and distribution near sea lion rookeries. Tagging experiments are being used to estimate abundance and movement between areas open and closed to the Atka mackerel fishery.

During the years 1999-2003, NMFS released roughly 32,000 tagged fish in Seguam Pass, 14,520 near Tanaga Island and 14,700 near Amchitka Island. In July 2006 approximately 7,900 fish were released near the Kiska Island area, and 7,200 fish near the Seguam Pass area. This FIT recovery charter recovered tagged fish in Seguam Pass and the Kiska Island area.

The cruise lasted for 22 days, beginning on 11 October in Dutch Harbor, Alaska, and ending in Dutch Harbor on 2 November. A total of 75 tows were conducted with 44 tows in Seguam Pass (Fig. 6) and 31 tows near Kiska Island (Fig. 7). A total of 1,786 t of Atka mackerel were examined for tags. Approximately 1,006 t were caught in Seguam Pass and 780 t were caught near Kiska Island. During the cruise a total of 59 tagged Atka mackerel were recovered, 4 in Seguam Pass and 55 near Kiska Island.

  Figure 8, see caption
Figure 8.  Percent length frequency distributions by sex for Atka mackerel during the recovery cruise in 2006 in Seguam Pass (3a) and the Kiska Island area (3b). There were too few males in spawning color in the Kiska Island area to include in this graph.

Tag reporting rates were estimated by seeding the catch with tagged fish. Reporting rates were high and averaged approximately 94% for single-tagged fish and 100% for double-tagged fish. In addition to tag recoveries, catch composition was determined, and sexed length frequencies and biological samples were collected for every haul. Biological samples consisted of gonads, stomachs, and age structures from randomly selected fish. During the course of the cruise, 620 biological samples and 11,394 sexed length data were collected.

Figure 8 illustrates the percent length frequency distributions for Atka mackerel during the 2006 recovery cruise in Seguam Pass and the Kiska Island area. The length-frequency distribution of fish at Seguam Pass was similar for both sexes and unimodal at 40-41 cm. The length distribution of fish in the Kiska Island area was a unimodal distribution at 37 cm for males and 36 cm for females. There seemed to be a slightly greater proportion of males at Kiska than at Seguam Pass where there was a slightly greater percentage of females.

During this cruise we recorded length frequencies for males in spawning color separately to identify spawning habitat. It appeared that in October the proportion of males in spawning color was overall small with a unimodal distribution of 39 cm at Seguam Pass. There were very few males in spawning color at the Kiska Island area, therefore those data are not shown.

The length frequency data, species composition data, and biological samples collected during this cruise will give us insight into the population structure and will be used for studies on Atka mackerel reproductive ecology and food habits. Some of this information will be incorporated into an integrated tagging model as auxiliary information modeling Atka mackerel population dynamics.

By Susanne McDermott, Libby Logerwell, and Kim Rand

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