Partial migration in the northern Gulf of St. Lawrence Atlantic cod population

No abstracts are to be cited without prior reference to the author.

The coexistence of resident and migratory individuals within a population is termed partial migration. Using data storage tags that record depth and temperature, we investigated the migratory behaviour of adult Atlantic cod in the northern Gulf of St. Lawrence. The geolocation problem was solved using the hidden Markov model based on daily maximum depths and bottom temperature. Reconstructed migration routes revealed undocumented partial migration in the panmictic population. Migratory individuals overwintered in relatively deep (300-500m) and warm (5°C) waters. In the spring, these migratory fish displayed extensive diel vertical movements that were interpreted as spawning behaviour. Resident individuals displayed a prolonged period of dormancy in shallow (< 50m) and near freezing (-1.5°C) coastal waters during the winter and the spring. This dormancy period was followed by foraging movements in western Newfoundland coastal waters. Limited ability of scientific survey to sample resident cod in shallow coastal waters may induce bias in the population abundance estimations.