Northern cod (<scp><i>Gadus morhua</i></scp>) movement: insights from acoustic telemetry and genomics

Knowledge of the timing and diversity of fish movements within a commercially exploited stock complex is required to ensure the sustainability of fisheries. Although migration can be driven by environmental factors, genomic mechanisms also play an important role in this complex life-history trait. The northern cod (Gadus morhua) stock complex, off the coast of Newfoundland and Labrador, once supported the largest fishery in the world. Like other Atlantic cod stocks, northern cod is believed to include components with diverse migratory patterns. Here we used telemetry to track the movement of 847 acoustically tagged northern cod caught and released from inshore and offshore sites. Four different migratory phenotypes were distinguished: (i) cod that moved along the Northwest Atlantic Fisheries Organization (NAFO) Divisions 2J3KL (3P4RS), (ii) cod that remained year-round mainly north of the Notre Dame Channel (NAFO Divisions 2J and north of 3K), (iii) cod that remained year-round mainly south of the Notre Dame Channel (NAFO Divisions south of 3K and 3L) and (iv) cod that remained year-round inshore. Whole-genome sequences of 77 tagged cod showed no relation between chromosomal inversions and the four migratory phenotypes described here but revealed genomic regions encoding for hormone receptors that show differentiation between cod detected north versus south of the Notre Dame Channel during the peak spawning season. This study demonstrates the synergistic value of an interdisciplinary approach that combines genomic with acoustic telemetry data along with life-history information (i.e., spawning time) to elucidate the complex spatial-temporal dynamics of a widespread marine species under exploitation.