The complex relationship between weight and length of Atlantic cod off the south coast of Newfoundland

Abstract

The relationship between the length and weight of fish is used to assess their growth and condition. This relationship is often assumed to be the same spatially and temporally. However, variability in the weight–length relationship can occur, which provides important information about stock productivity. We developed a spatiotemporal model for the weight–length relationship that is useful for predictions in un-sampled areas. We applied the model to survey data for Atlantic cod off the southern coast of Newfoundland, Canada. We found that weight-at-length was higher inshore, oscillated over time, was below average in recent years, declined during late-January to early-June especially for intermediate sized cod, and that the temporal oscillations were correlated with several local environmental time series. Finally, the model estimated a decrease in the allometric coefficient for intermediate sized cod (40–80 cm), indicating that those cod may be experiencing additional feeding deficiencies. Spatiotemporal variation in the weight-at-length relationship should be accounted for in the stock assessment process when fishery catch numbers are derived from tonnes landed and when estimating stock and fishery weights-at-age.