Variation in fish condition between Atlantic cod (Gadus morhua) stocks and implications for their management

Abstract

A comparative analysis of the fish condition (Fulton’s K) of 11 cod stocks in the North Atlantic in relation to the temperature of their habitat and their reproductive potential is presented. It is shown that the cod stocks in the North Atlantic display different levels of mean condition, which are partly due to the different temperature regimes of their habitats. Cod stocks living in colder waters, e.g. Southern Gulf of St Lawrence, Greenland and Grand Bank cod stocks, were more poorly-conditioned than cod stocks living in warmer waters, e.g. North Sea and Irish Sea. The a-coefficient obtained from a standardised Ricker’s recruitment-spawning stock biomass (SSB) relationship represents the function’s slope at the origin and was defined as an indicator for the recruitment potential of a given stock. The a-coefficients were found to be correlated with the mean condition factors of the stocks in 9 of the 11 cod stocks analysed. This indicates that stocks consisting of poorly-conditioned individuals appear to be very susceptible to reduced recruitment at low SSB, while the stocks which consist of well conditioned fish seem to behave more robust with a higher probability of good recruitment at low SSB. The positive effect of the cod condition on their reproductive potential generally implies that the well-conditioned stocks in the Northeast Atlantic can sustain higher exploitation rates than the poorly-conditioned stocks in the Northwest Atlantic. This implication is confirmed by a positive relationship between the estimated biological management reference points Fmed and the mean cod condition factors of the stocks.