Impact of ocean warming on sustainable fisheries management informs the Ecosystem Approach to Fisheries.

An integrated ecosystem model including fishing and the impact of rising temperatures, relative to species' thermal ranges, was used to assess the cumulative effect of future climate change and sustainable levels of fishing pressure on selected target species. Historically, important stocks of cod and whiting showed declining trends caused by high fisheries exploitation and strong top-down control by their main predators (grey seals and saithe). In a no-change climate scenario these stocks recovered under sustainable management scenarios due to the cumulative effect of reduced fishing and predation mortalities cascading through the food-web. However, rising temperature jeopardised boreal stenothermal species: causing severe declines in grey seals, cod, herring and haddock, while eurythermal species were not affected. The positive effect of a higher optimum temperature for whiting, in parallel with declines of its predators such as seals and cod, resulted in a strong increase for this stock under rising temperature scenarios, indicating a possible change in the contribution of stocks to the overall catch by the end of the century. These results highlight the importance of including environmental change in the ecosystem approach to achieve sustainable fisheries management.

Implications of a warming North Sea for the growth of haddock Melanogrammus aeglefinus.

The present study aimed firstly, to test for a temperature effect on North Sea haddock Melanogrammus aeglefinus growth and secondly, to develop a model that could be used to assess total length (L(T)) and mass (M)-at-age response to different temperature scenarios. The von Bertalanffy growth model was fitted on a cohort-by-cohort basis from 1970 to 2006. The asymptotic L(T) (L(∞)) was negatively correlated with temperature while the rate at which L(∞) is reached (K) was positively correlated with temperature. K was negatively correlated with density, whereas no effect on L(∞) was observed. These effects were incorporated into a von Bertalanffy model which was extended to include temperature and density as explanatory variables. Only the temperature variable was significant. Fitting the extended von Bertalanffy model revealed that L(∞) decreased while K increased with increasing temperature, resulting in up to a 40% loss of individual yield at older ages. The dramatic decline observed in the mean age at which 50% of the population becomes mature suggests that higher temperatures resulted in larger young M. aeglefinus that matured earlier and therefore reached a smaller maximum size. In a global warming context, the loss of individual yield observed at old ages is likely to reduce the fisheries yield for M. aeglefinus in the North Sea.