COD SPAWNING ON A MIGRATION HIGHWAY IN THE NORTH-WEST ATLANTIC

FIVE hundred years of fishing and fifty years of research have produced only vague accounts of the spawning and migrations of Atlantic cod (Gadus morhua) off Newfoundland in the north-west Atlantic1. Here I report the discovery of 'spawning columns' and a 'highway' used by cod to traverse the northeastern Newfoundland Shelf during annual springtime feeding migrations. Sea research using echosounders2,3 showed that cod spawned in dense shoals (to one fish per m3) that featured midwater spawning columns comprised of pairs of fish. Immature joined mature post-spawning cod to migrate in large (scales of tens of kilometres and hundreds of millions of fish) size-structured aggregations led by larger 'scouts'. Cod traversed the cold waters of the shelf along a deep highway of warm oceanic water (2-2.5-degrees-C). During migration, fish spacing appeared to maximize search volumes while maintaining visual contact. Aggregations fragmented when prey (capelin Mallotus villosus; shrimp, Pandalus spp.) were encountered.