Feeding habits of allis shad Alosa alosa (Linne, 1766) and twaite shad Alosa fallax (Lacepede, 1803) in the bay of Biscay.

Stomach contents of 193 Alosa alosa (181-538 mm total length TL; 2-4 years old) and 175 Alosa fallax (204-486 mm TL; 2-6 years old) caught throughout the French continental shelf area of the Atlantic ocean show that shads mainly select pelagic preys. A. alosa is zooplanktonophagous species. The major prey items are euphausiacea; copepoda are an additional prey. Fish, anchovies and sprats (Engraulis encrasicolus Sprattus sprattus) are incidentally cosumed during the year. A. fallax is predominantly ichthyophagous. It feeds preferentially on anchovy all over the year. In Spring, euphausiacea occur more often in the bulk but they are only secondary preys. The lowest feeding period for the two species of shad occurs during summer. Coefficient of condition decreases during that season. Feeding intensity of twaite shad rises 4-8 hours after sunrise.