A review of the importance of various areas for northern contingent West-Atlantic mackerel spawning

Abstract

The southern Gulf of St. Lawrence (sGSL) is considered to be the dominant spawning area of northern contingent West-Atlantic mackerel (Scomber scombrus). This premise underlies our basic understanding of the stock and its assessment. Because there are however indications of spawning outside the sGSL, we aimed to review the potential importance of various external regions for spawning, based on a weight of evidence approach. Fundamentally, important spawning areas can only exist where there is evidence of a considerable spawning stock biomass being present when environmental conditions are suitable for spawning. This should lead to direct observations of significant egg and larval densities. Based on an ensemble of evidence (migration patterns, environmental conditions, and ichthyoplankton observations), we investigated the dominance of the sGSL for northern contingent mackerel spawning. Elsewhere, such as on the Scotian Shelf, where mackerel starts its spring migration, there is evidence of minor but relatively consistent egg production. Spawning off Newfoundland, where mackerel can migrate to later in the year, appears sporadic and highly variable in intensity. This review should alleviate some of the uncertainty associated with the mackerel stock assessments and be a baseline to further our knowledge on mackerel spatial spawning dynamics.