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AFSC/ABL: Taku chum salmon project diet and energy database
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This study is a cooperative effort between Douglas Island Pink & Chum (DIPAC), the
University of Alaska Fairbanks, School of Fisheries and Ocean Sciences (UAF, SFOS),
the National Oceanic & Atmospheric Administration, Auke Bay Lab (ABL), and the Alaska
Department of Fish & Game (ADF&G) to determine the potential for interactions between
DIPAC hatchery chum salmon (Oncorhynchus keta) fry and wild chum salmon fry in Taku
Inlet, Southeast Alaska. We analyzed patterns in spatial and temporal distribution,
size, and condition of juvenile chum salmon collected in the littoral and neritic
waters of Taku Inlet in 2004 and 2005. Energy density and diet of wild and hatchery
chum salmon fry in Taku Inlet were analyzed and compared to data obtained later in
the season for chum salmon stocks caught in Icy Strait. The greatest potential for
wild/hatchery interactions was in the outer inlet, directly following early hatchery
releases (May 9-11). Peak outmigration for wild chum salmon fry coincided with early
hatchery releases; in contrast, most wild chum salmon fry had already emigrated from
the estuary by the time of late hatchery fry release (May 22 June 1). In both years,
hatchery fry were rare in the inner inlet, but comprised over 95% of the catch in
the outer estuary during the peak of outmigration. Hatchery chum salmon were significantly
larger than wild fry in both beach and neritic samples. Wild and early hatchery chum
salmon were smaller in the littoral than the neritic habitat, indicating that both
groups moved from shallow to deeper water with ontogeny. In spite of large differences
in abundance, no negative correlation between abundance of hatchery fish and condition
of wild fish was identified. Both wild and early hatchery chum salmon fry showed apparent
growth through the season, while late hatchery fry appeared to leave the estuary soon
after release. Regardless of origin, most chum salmon juveniles emigrated from the
study area in late May and early June, indicating a high probability for mixed-stock
schools. Hatchery chum salmon juveniles were initially larger and had greater
energy content than wild fish; however, energetic values converged by mid-June in
Taku Inlet. In Icy Strait, energetic condition of wild and hatchery chum salmon juveniles
was also similar. Multivariate analysis of 54 prey measures indicated that diets of
the two groups were distinctly different throughout the season in all Taku Inlet locations
and converged in Icy Strait.
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