Response of individual shoaling Atlantic cod to ocean currents on the northeast Newfoundland Shelf

Abstract

The movements of sonically-tagged Atlantic cod swimming within a large (80,000 mt) shoal of post-spawning fish on the northeast Newfoundland Shelf were related to the acoustically determined position of the shoal and event structure in the local ocean currents. For the first several days of the study, a period when currents were unfavorable for shoreward transport, the tagged fish maintained station. There was little net movement of individual fish and no change in the geographical location of the shoal. Then, apparently in response to a shoreward current event, the cod moved with the flow. The tagged cod behaved as members of the shoal, in that their net movement was similar to that of the shoal itself. These observations further support the hypothesis that cod on the northeast Newfoundland Shelf selectively use currents for transport during their shoreward feeding migration. The cue to initiate migration by post-spawning cod is apparently an organized onshore flow exceeding a threshold velocity and duration.