Research Document - 2006/019

A review of predator-prey and competitive inter-specific interactions in Atlantic salmon (Salmo salar)

By Cairns, D.K.

Abstract

This paper reviews Atlantic salmon (Salmo salar) feeding behaviour, prey, predator relations, and competitive interactions. Juvenile salmon feed heavily in spring, less heavily in summer and fall, and minimally in winter. Diurnal feeding cycles are variable in summer, but in winter juveniles are nocturnal. Juvenile Atlantic salmon typically feed by darting up from home stations to seize passing prey. Juveniles in streams feed on aquatic invertebrates, including Ephemeroptera, Plecoptera, Trichoptera, Chironomiidae, and Coleoptera. Smolts on their downstream migration also feed on aquatic invertebrates. Growth in marine waters is much more rapid than in stream habitat. Marine-phase Atlantic salmon feed most heavily in spring. Post-smolts eat mostly invertebrates, while larger salmon eat a higher proportion of fish. Marine-phase salmon occupy the middle and upper layers of the water. Capelin, sand lance, herring, and a variety of crustaceans are among the principal foods of marine-phase salmon in the Northwest Atlantic. Atlantic salmon eggs may be consumed by ducks and by Atlantic salmon. Atlantic salmon fry and parr are consumed by birds, particularly common mergansers, belted kingfishers, and double-crested cormorants, and fish, including Atlantic salmon, trout, eels, and smallmouth bass. Under predation threat juvenile Atlantic salmon either freeze, relying on cryptic coloration, or dash for cover. Outmigrating smolts may be eaten by cormorants and other birds, seals, and by a variety of fish. In the open sea salmon are taken by predatory fish, birds, and seals. Adult salmon returning to their native rivers are subject to seal predation. Atlantic salmon in freshwater compete for resources with conspecifics and with other species, particularly other salmonids. Atlantic salmon competitively displace brook and rainbow trout from riffle habitat, but trout are stronger competitors in slow water. Wintering juvenile Atlantic salmon require rocky cavities for daytime shelter, which may be subject to intense inter- and intra-specific competition. In the ocean, competitive interactions between Atlantic salmon and other species have not been experimentally investigated. It is unlikely that nutrient flux due to Atlantic salmon contributes significantly to freshwater productivity.

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