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

Abstract

In May of 2012 to 2015, 90 large (85-117 cm) Northern cod (Gadus morhua) with pop-up satellite archival tags (PSATs) set to release one year later were released from offshore spawning aggregations on the northeast Newfoundland shelf. Forty-nine (54%) transmitted or were recovered; 82% migrated inshore, 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 5o longitude (350 km) and 2o 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 oC) 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 Dec 1st was 50%, which could impact time-dependent surveys. Fishing exploitation was 6%, predation 5%. Northern cod have re-established historical spatial migration patterns, with capelin a key influence on timing and duration inshore.