Temporal evolution of critical traits and their relationship to cod stock collapse and recovery

Abstract

The North Atlantic Fisheries Organization response to a precipitous decline of the Flemish Cap cod ( Gadus morhua) stock during the 1990s was the imposition of an 11 year moratorium on directed fishing for cod; recovery followed. Over the three decades that encompassed the precollapse, collapse, and recovery stages, we found that the cod stock status was characterized by four traits: spawning stock biomass, maturity-at-age, weight-at-age, and recruitment. The temporal evolution of these traits was consistent with a density-dependent conceptual model suggesting that phenotypic plasticity was at play during the rebuilding of the stock. The temporal progression of the broader fish community paralleled that of cod, underlying its key ecosystem position. The same demographic variables defined the state of the adjacent Northern Cod stock that underwent a similar pattern of decline, an intermittent moratorium but only partial recovery. This partial recovery is possibly related, in part, to declines of prey species brought about by excessive harvesting after the cod collapse and an apparent collapse of capelin, a major dietary component.