Demographic characteristic of Alosa fallax rhodanensis (Clupeidae) populations in the French Mediterranean area.

Morphological and biological characteristics of twaite shad (Alosa fallax r hodanensis) populations in the French Mediterranean area are presented. Res ults were obtained from analysis of adults sampled during upstream migratio n in the Rhone, Aude, Herault and Tavignano Rivers. Populations were analys ed in terms of demographic structure (age class distribution, mean age at u pstream migration, age at sexual maturity, sex ratio and number of reproduc tions) and of biometry (length-weight per age class). Results, showing that the Mediterranean populations have a higher size, a greater longevity and an older AMR than Atlantic populations, are discussed. These characteristic s bring Mediterranean french twaite shads closer to Allis shed (A. alosa).