The port of Mahdia and its fishing region is of local and national importance for fishing and the marketing of seafood. However, for more than a decade fishermen have felt that the quantity and quality of the seafood. Sin product has degraded. This degradation affected fish, molluscs and crustaceans. Likewise, the biodiversity of their fishing areas has been disturbed by the disappearance, appearance or modification of the appearance of the frequency of certain areas. Thus, the structure of the fishing stand seems to be disturbed. The size of some species caught has reduced, and for other species, the geographic range or depth of fishing is no longer 100/100% the same. For the causes of these disturbances, they could be one of the consequences of the excessive exploitation of fishing, which is known for its destructive effect on the population of fish, crustaceans or molluscs, and of degradation of the world stock of fishery products. . However, the cause which better explains this phenomenon of change of the environment, described by the answers to the questions asked to the fishermen, is the phenomenon of "climate change". Indeed, many of these changes in the biotic and abiotic environment of the marine area studied are internationally known to be the direct or indirect result of global warming of the environment.