Commercial catch rates of the clam Spisula solida reflect local environmental coastal conditions

The effect of environmental variables and fishing pressure (explanatory variables were lagged 1 year) on commercial catch rates of the clam Spisula solida was studied on an annual basis over a 21 year period in three areas off the Portuguese coast (the Northwest, the Southwest and the South) between 1989 and 2009. Each area showed distinct environmental (oceanographic and hydrological) characteristics. Different sensitivities of S. solida fishing grounds to environmental variables were found among the study areas. On the Northwest coast, the combined effect of NAO indices and sea surface temperature had a positive effect on S. solida fisheries, particularly during the spawning season. On the Southwest coast, the variation of S. solida catches was negatively associated with wind magnitude and positively related with South-Southeast winds. Winter river discharges and summer sea surface temperature negatively affected S. solida catches on the South coast. Fishing effort also affected S. solida catch rates in the South. However, “extreme” changes in environmental conditions were the main drivers of short-term variations in catch rates. These results indicate that variations of S. solida catches strongly reflect a regional signature of local climatic features off the coast. Information on local environmental conditions should therefore be used for the purpose of identifying management actions to ensure long-term sustainability of S. solida fisheries.