Congruence of stock production and assessment areas? An historical perspective on Canada’s iconic Northern cod

Abstract

Fisheries management requires spatially congruent production and assessment areas. Canada’s Northern cod (Gadus morhua), initially considered a stock complex distributed from northern Labrador to the northern Grand Bank, had its northern boundary reduced to southern Labrador in the early 1970s. Spatial incongruence has resulted in spawning stock biomass (SSB) and recruitment (R) between historical and recent eras. To investigate temporal changes, four stanzas of SSB and R were derived from statistical Perron breaks. In stanza 1, the 1960s, spawning off northern Labrador coincided with higher SSB and R than in following stanzas from the 1970s onward. SSB–R relationships that include 1960s data do not represent potential production from a more southerly distributed stock. Loglinear models of R (density-dependent models did not improve fit) indicated SSB had greatest effect and, with indices of climate and south–north distribution, explained 86% of variance. Lack of density dependence suggests long-standing recruitment overfishing, making reference points problematic. SSB growth is suggested as an alternative management target. Rebuilding the Northern cod to historical abundance requires a full “portfolio” of spawning from northern Labrador to the Grand Bank (a remanaged 2+3KL stock). With a contracted range, lower production should be anticipated.