Is spawner biomass a sensitive measure of the reproductive and recruitment potential of Northeast Arctic cod?

Abstract

The assumption that spawner biomass is directly proportional to total egg production by fish stocks underlies most spawner-recruit relationships. Despite its importance, this assumption is largely untested. Data describing the reproductive potential of Northeast Arctic (NEA) Atlantic cod (Gadus morhua) were used to test the proportionality assumption for a period showing strong variation in condition and abundance of spawners. At the individual scale, relative fecundity varied with length and condition. This decreases the likelihood that the proportionality assumption is valid. At the stock level, total egg production was estimated (1985-1996) using acoustic estimates of total abundance and demographic information from trawl sampling in combination with year-specific fecundity-length relationships. For NEA cod, spawner biomass estimated by virtual population analysis (VPA) was not proportional to total egg production. Compared with VPA-based estimates of spawner biomass, total egg production is an improved index of recruitment potential because (i) the magnitude of variation observed in total egg production was closer to that observed in recruitment and (ii) the relationship between recruitment at age 1 and total egg production approaches the origin. The results suggest that further progress in explaining recruitment variation will be achieved using more sensitive measures of the true reproductive potential of the stock.