The main objective of this study was to design a method able to forecast gonadal stages in Chamelea gallina based on the influence of environmental conditions. This tool could be used to improve its fishery management since natural beds have been extremely overexploited during the last few decades on the European coasts and populations have severely decreased. The natural population’s reproductive cycle was studied from November 2013 to June 2016 (32 months). Gonadal and condition indexes (GI and CI) values were statistically related to environmental conditions: surface seawater temperature (SST) and chlorophyll-a (Chlo-a). Among all the correlations made, the highest R2 value (p < 0.001) was found between GI and the SST registered 60 days before bivalve sampling (SST-60). The regression equation derived from this correlation allows estimate the GI value if the SST-60 values are available. Each GI value is related with one gonadal stage (resting, maturation, ripe) and this allows for forecasting 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 colors onto a map of striped venus´ reproductive stages in its natural beds.