Sex Ratio and Potential Fecundity of Atlantic Salmon (Salmo salar L.) Caught by Anglers on the Elorn River (Northern Brittany, France) during 1979 and 1980

Analysis of the sex ratio of angling Atlantic salmon catches from March to mid-June on the Elorn river in 1979 and 1980 showed a majority of females among the spring salmon population. Comparison between serodiagnostic technique and visual observations of gonads indicated that the former method provided a very low error margin for sex ratio determination on all females in the early stages of maturation and entering rivers. Study of sexual characteristics of spring salmon bearing copepod parasites or not indicated that fish entering freshwater would initiate a new stage of the ovogenesis process characterized by a failure of about 30% of the oocytes and a correlation between fecundity and size that did not exist at the time of the entry into freshwater.