Research Document - 2003/060

Cod stocks rebuilding and fish bioenergetics : low productivity hypothesis

By Dutil, J.D., Gauthier, J., Lambert, Y., Fréchet, A., Chabot, D.

Abstract

The lack of response of several cod stocks and other species to management regulations expected to promote stock rebuilding is hypothesized to stem from a combined (multiplicative) effect of 3 factors : 1. natural intrinsic productivity is low; 2. natural intrinsic productivity has declined; 3. pressures on production associated with natural and fishing mortality have remained high or have increased relative to these stocks/species rates of production. Annual production per capita and per unit biomass varies among stocks, with northerly distributed stocks or stocks inhabiting cold and sometimes hypoxic environments being notably less productive than other stocks. Cod in less productive stocks grow slowly, recruit at an older age, become sexually mature at a later age and a smaller size and produce fewer eggs. Fish condition is on average lower and varies much more in these stocks compared to other stocks. Environmental conditions have changed progressively after the mid '80s with conditions during the moratorium not favorable to cod production in northern areas of the western North Atlantic. Fish stocks in these areas have thus become less productive and hence less resilient, i.e., less able to resist and respond to perturbations, whether man-made or environmental. There are several recent indications that individual performance has improved, but fishing pressure has not been relaxed sufficiently to offset increased predation pressures and low productivity associated with limiting environmental conditions. These stocks are unable to produce new biomass fast and as a result stock rebuilding is expected to take much longer than would be predicted for other stocks living in more favorable environments, particularly if exploited under enduring adverse environmental conditions. Strengths and weaknesses of this hypothesis are discussed.

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