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AFSC/ABL: Genetic data for juvenile chum salmon samples collected in the eastern Bering
Sea on the U.S. BASIS cruises during 2003-2007.
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Chum salmon (Oncorhynchus keta) are an important natural resource in western Alaska
for subsistence, commercial and cultural reasons. Declines in chum salmon returns
in some western Alaska drainages over the last couple of decades have prompted regulatory
changes and bolstered research on this species in this region. Since 2002, juvenile
chum salmon have been collected as part of the annual U.S. Bering-Aleutian Salmon
International Survey (BASIS) during the late summer/fall season in the eastern Bering
Sea. From the 2003-2007 collections, nearly 5,000 juvenile chum salmon samples were
genetically analyzed. With the available microsatellite baseline, regional stock estimates
were produced from mixed-stock analyses. The proportions of juvenile chum salmon
from four western Alaska regionsNorton Sound, lower Yukon (summer-run), upper Yukon
(fall-run), and Kuskokwim/northeastern Bristol Baywere remarkably similar across years
during early marine residence, especially given the latitudinal shifts from year-to-year
in the distribution across the eastern Bering Sea shelf of this highly migratory species.
Most of the juvenile chum salmon were from the Yukon River, which has two life-history
types, an earlier and typically more abundant summer run, and a later fall run. The
Kuskokwim/northeastern Bristol Bay contribution within the study area (lat. 58-63N)
was negligible, indicating that these stocks do not migrate northward during their
first summer. The Norton Sound group contribution varied annually, but in general,
increased with latitude. These results support a migration model whereby western
Alaska juvenile chum salmon, after leaving freshwater, head primarily west and south
across the eastern Bering Sea shelf. A relative abundance index was developed from
the proportions of the two life-history types in the Yukon River of juvenile chum
salmon in the survey area. In all five years of collections, the summer-run contribution
was higher than the fall-run contribution in the juvenile chum salmon samples. The
proportions of the two life-history types in the juvenile chum salmon collected at
sea were compared with those in the Yukon River adult returns. A correlation was found
between the juveniles and subsequent adult returns. This suggests that it is during
the period of freshwater and early marine residence that the cohort strength of Yukon
River summer- and fall-run chum salmon is determined.
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