Lack of trophic competition among wild and hatchery juvenile chum salmon during early marine residence in Taku Inlet,Southeast Alaska |
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Authors: | Email author" target="_blank">Molly?V?SturdevantEmail author Emily?Fergusson Nicola?Hillgruber Carl?Reese Joe?Orsi Rick?Focht Alex?Wertheimer Bill?Smoker |
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Institution: | (1) Auke Bay Laboratories, Alaska Fisheries Science Center, National Marine Fisheries Service, 17109 Pt. Lena Loop Rd, Juneau, AK 99801, USA;(2) Juneau Center, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 17101 Pt. Lena Loop Rd, Juneau, AK 99801, USA;(3) Alaska Department of Environmental Conservation, 410 Willoughby Avenue, Juneau, AK 99801, USA;(4) Douglas Island Pink and Chum, Inc, 2697 Channel Drive, Juneau, AK 99801, USA |
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Abstract: | Early marine trophic interactions of wild and hatchery chum salmon (Oncorhynchus keta) were examined as a potential cause for the decline in harvests of adult wild chum salmon in Taku Inlet, Southeast Alaska.
In 2004 and 2005, outmigrating juvenile chum salmon were sampled in nearshore habitats of the inlet (spring) and in epipelagic
habitat at Icy Strait (summer) as they approached the Gulf of Alaska. Fish were frozen for energy density determination or
preserved for diet analyses, and hatchery stocks were identified from the presence of thermal marks on otoliths. We compared
feeding intensity, diets, energy density, and size relationships of wild and hatchery stocks (n = 3123) across locations and weeks. Only hatchery fish feeding intensity was negatively correlated with fish abundance. In
both years, hatchery chum salmon were initially larger and had greater energy density than wild fish, but lost condition in
early weeks after release as they adapted to feeding on wild prey assemblages. Diets differed between the stocks at all inlet
locations, but did not differ for hatchery salmon between littoral and neritic habitats in the outer inlet, where the stocks
overlapped most. Both diets and energy density converged by late June. Therefore, if density-dependent interactions affect
wild chum salmon, these effects must be very rapid because survivors in Icy Strait showed few differences. Our study also
demonstrates that hatchery release strategies used near Taku Inlet successfully promote early spatial segregation and prey
partitioning, which reduce the probability of competition between wild and hatchery chum salmon stocks. |
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