REPRODUCTION, CONDITION AND FOOD OF ADULT ARCTIC CHARR (SALVELINUS-ALPINUS, L) IN LAKE PAVIN (MASSIF-CENTRAL, FRANCE)

To determine the role and the importance of adult fish predation directly and indirectly in the food web of oligomesotrophic Lake Pavin, reproduction, condition, and feeding activity of the dominant adult arctic charr (Salvelinus alpinus, L.) were studied. Fish were caught by gillnets of different mesh sizes once a month from April to December 1992. The gonad cycle showed that the spawning period occurred between October to December. Relative fecundity is about 2509 ovules per kg of female fish and ovule mean diameter is 4.7 mm (+/-0.6 mm). Seasonal variations of the sex-ratio (Max. in April = 2.67 and Min. in October = 0.19) indicated the intralake migrations of females and males. The condition coefficients showed higher values for females than males; the maximum was observed in summer for both sexes and the minimum in April and in October for males and females, respectively. Low values of the condition were also observed during the spawning period. High feeding activity was recorded in spring and in December after reproduction; low feeding activity was observed in October during reproduction. Asellus aquaticus was quantitatively the dominant prey from April to September; during the spawning period, S. alpinus consumed its own eggs, particularly in large quantity in December. Daphnia longispina was numerically the dominant prey all over the studied cycle and the electivity (Ivlev Index) of arctic charr on the latter prey ranged from +0.79 to +0.16. During April more than 15 500 individuals of D. longispina per Lo nf fish were found in the guts contents. The selective predation of S. alpinus on benthic (A. aquaticus) and zooplankton prey (D. longispina) indicated that the fish immigrate during their feeding activity from benthic/littoral to the pelagic area.