Improving bivalve fishery management: The development of a tool to forecast bivalve reproductive season based on environmental data from satellite remote sensing observations

Donax trunculus is a much-appreciated commercial clam whose natural populations have been overexploited in southern-western Spain during the last decades. In order to control the decrease of natural beds, local governments establish annual closed seasons based on socioeconomic reasons, such as economic necessity or tourism interest. The objective of this study was to develop an efficient tool for predicting gonadal stages based on environmental condition data. This tool will allow for an improvement in fishery management since in this manner the closed season can be based on the reproductive cycle. The natural population's reproductive cycle was studied for more than 2 years. The obtained gonadal and condition indexes (GI and CI) values were statistically related to environmental conditions, specifically surface seawater temperature (SST) and chlorophyll-a (Chlo-a) levels with these data being provided from satellite remote sensing observations (SRS). The best statistical relationship was obtained between GI and the SST registered 60 days before bivalve sampling (SST-60). The regression equation allows for an estimate of GI value based on the SST-60 and, as each value is related with one gonadal stage (resting, maturation, ripe), for prediction of the reproductive cycle. Therefore, the closed season can be established when most of the population is in the ripe stage and can be adjusted taking into account the possible temperature variations across the years. For ease of use, GI values estimated with this tool have also been converted using different colours onto a map of wedge clam reproductive stages in its natural beds.