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Predation impacts of gadid fish and seagulls on migrating smolts in Norway

The predation on seaward migrating salmonid post-smolts can be a major regulating factor for local populations of salmon and sea trout. In freshwater, and especially in the transition zone from river to the sea, avian predators have been reported to be of importance.

During the study of the behaviour and migration of salmon smolts, several of the tagged smolts were eaten by gulls or predatory fish within few hours after descent. Through visual observations and stomach analyses, the predation from saithe (Pollachius virens L.) and cod (Gadus morhua L.) on seaward migrating Atlantic salmon (Salmo salar L.) and anadromous trout (Salmo trutta L.) post-smolts, the results indicate that some saithe may have specialized in preying on post-smolts.

Wild and hatchery-reared post-smolts were eaten at equal rates. For smolt releases in both enhancement strategies and in telemetry studies, predation as a population regulating factor in various fjord systems should also be considered.

Reported by

Norwegian Institute for Nature Research
Tungasletta 2
N-7485 Trondheim
Norway
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