Northern cod re-establish historical migration patterns linked to capelin: insights from pop-up satellite archival tags

Abstract

In May 2012–2015, 90 large (85–117 cm) Northern cod ( Gadus morhua) with pop-up satellite archival tags (PSATs) set to release 1 year later were released from offshore spawning aggregations on the northeast Newfoundland shelf. Forty-nine (54%) transmitted or were recovered; 82% migrated inshore and 15% remained offshore (balance predated). Geo-locations were based on release, capture, and surfacing positions, and at tag-recorded depths <50 m, on Kalman-predicted light-based longitudes matched with coastal bathymetry. Migrating fish moved southwestward on average 5° longitude (350 km) and 2° latitude (222 km) to the northeast coast of Newfoundland, southern Labrador, and northern Grand Bank, as historically from similar release points. Migration onset through the Labrador Current (<0 °C) and arrival inshore were correlated with capelin ( Mallotus villosus) peak spawning, inshore duration with capelin, and cod biomass. Both species were delayed a month from historical norms. The probability of a cod remaining inshore after 1 December was 50%, which could impact time-dependent surveys. Fishing exploitation was 6% and predation 5%. Northern cod have re-established historical spatial migration patterns, with capelin a key influence on timing and duration inshore.