The impact of water circulation on the year-class abundance dynamics of redfish and cod on the Flemish Cap

Abstract

This paper studies the formation of abundance of redfish (Sebastes spp) and cod (Gadus morhua) year-classes under varying conditions of spawning, of which a key role is played by water circulation. A statistically significant relationship (r=0.601, p=0.002) between survival of cod year-classes and atmospheric cyclonic activity was revealed. This relationship is based on the effect of storms on water circulation over the Flemish Cap and supports the hypothesis on the impact of year-to-year variation in the Taylor column circulation on the cod survival. By contrast with cod, the survival of larval redfish is to a large extent related to the position of the North Atlantic Current, which impacts on the main spawning grounds (southern slopes of the bank) and correspondingly may influence the drift of larvae away from the bank. This is supported by a reciprocal relationship (r=-0.565, p=0.012) between redfish survival rate on the Flemish Cap and position of the northern front of the Gulf Stream by latitude south of the Grand Banks near 51°W. The emergence of very strong year-classes of redfish in Div. 3M is likely to be related more to the hydrographic conditions rather than to the status of the spawning stock. It is most probable that a stronger anticyclonic eddy leds to increased year-class strength, while weak eddies result in a more powerful drift of larval and juvenile redfish away from the bank. In turn, the emergence of on year-classes may, in a way, be an "indicator" of specific types of water circulation on the bank.