Larval otolith growth histories show evidence of stock structure in Northeast Atlantic blue whiting (Micromesistius poutassou)

Oceanographic modelling studies suggest that blue whiting (Micromesistius poutassou) larvae released on the Northeast Atlantic spawning grounds split into two branches, one following a northerly drift trajectory and the second drifting towards the south. This mechanism is proposed to restrict gene flow between northern and southern stock components. This study examined larval growth histories recorded in otoliths of adult blue whiting from three regions of the main spawning area and three feeding areas for evidence of divergent dispersal pathways. Increment measurements show that fish from the south of the spawning area on average grew significantly faster as larvae than those from the north of the spawning area, confirming that blue whiting spawning west of Ireland and Scotland do not form a randomly mixing unit, and that larval dispersal influences the subsequent distribution of spawning adults. Larval otolith growth rates in feeding blue whiting from the Bay of Biscay were significantly faster than those of fish from the Norwegian Sea feeding grounds, showing that mixing of fish from these areas is limited. Fish from the Bay of Biscay grew faster as larvae than fish from all regions of the main spawning area. The results support the proposed split in the blue whiting stock and signal caution for managing the fishery.