Measuring sturgeon. Male biologist measuring a common Atlantic sturgeon (Acipenser sturio) before tagging it and releasing it back into the wild. This fish is now protected after declining dramatically in number in France during the 20th century. Its eggs can be pickled and eaten as caviar. Tagging enables the size and movements of the fish population to be determined, while measuring the fish's length provides data about its age and health. Photographed in the Gironde Estuary in France.