Salmon As Predators and Prey in Marine Waters of Alaska

Predation during the early critical period of rapid fish growth is thought to determine year class strength for juvenile salmon and many other species, yet surprisingly little has been published on the impact of specific marine predation. Predation impact is hard to document because it requires consistent sampling over extended periods to capture infrequent or episodic events. We examined diets of marine fish, including adult salmon, in migratory corridors from a 14-year time series (1997-2010) of surface trawl catches in Southeast Alaska and from two years (2009-2010) of purse seine test fisheries in southwestern Prince William Sound. Our objectives were to investigate four aspects of predation: a) the incidence of predation on juvenile salmon by adult/immature Chinook, coho, sockeye, chum, and pink salmon, b) piscivory on forage fish by adult salmon, c) the potential for cannibalism by odd-even year broodlines of pink salmon to depress adult returns the following year, and d) predation impact on juvenile salmon by an episodic strong year class of sablefish. We present highlights of research on these trophic interactions that could affect salmon recruitment.