A Drift–Retention Dichotomy for Larval Haddock (Melanogrammus aeglefinus) Spawned on Browns Bank

Abstract

This study was designed to assess the dispersal of haddock (Melanogrammus aeglefinus) larvae from their Browns Bank spawning site in terms of either drift or retention mechanisms. Larvae were collected in comprehensive surveys of southwestern Nova Scotia conducted at monthly intervals through the winter–spring of 1985. To avoid any confounding of larval displacement patterns by the numerically dominant young larvae, all spatial analyses were structured by age through otolith microstructure techniques. The results of a trend surface analysis indicated that both drift and retention processes operated in concert to split and disperse the larval population. Retention was probably physically based, through the action of a "leaky" gyre around Browns Bank. Although similar processes are believed to have influenced the distribution of Browns Bank cod (Gadus morhua) larvae, the interspecific difference in spawning time, coupled with the apparent instability of the gyre, produced a different balance between transported and retained larvae. A drift–retention dichotomy for Browns Bank ichthyoplankton has implications for both recruitment and stock structure studies.