Incorporating early-life history parameters in the estimation of the stock-recruit relationship of Georges Bank Atlantic cod (Gadus morhua)

Abstract

The determination of stock status and estimation of biological reference points for management of commercially important species often relies on a spawning stock-recruit function which typically assumes that spawners of all ages contribute equally to recruitment. Recent studies of cod (Gadus morhua), however, indicate that the viability of eggs spawned by large and old fish is greater than that of small and young fish. The current stock-recruit relationship for the Georges Bank Atlantic cod stock is based on recruitment of age 1 fish and spawning stock biomass (SSB) derived from virtual population analysis for 1978-2000. The stock-recruit relationship was re-examined by three component stages: egg production as a function of SSB, larval production as a function of egg production, and recruitment as a function of larval production. A statistically significant relationship (P <0.05) was detected for the eggs-SSB (1978-98) component but not for the eggs-larvae and larvae-recruits components although positive trends were observed during the time series (1978-86). Stepwise multiple regression suggests that the age diversity of repeat spawners, spatial distribution of spawned eggs, and bottom temperature contribute significantly to the estimation of variance in egg survivorship for the years 1979-98 (r2 = 0.54). The results of the eggs-SSB analysis support conclusions of other studies that repeat spawners have better survival of eggs and early larvae. In addition, these results emphasize that not only the total weight of SSB but also the age diversity of SSB contributes to enhanced recruitment.