RECOLONIZATION IN A DEVASTATED CORSICAN R IVER - RESPECTIVE CONTRIBUTION OF WILD AND DOMESTIC BROWN TROUT

The present study was carried out in the Abatesco River basin on the E astern coast of Corsica. In September 1989, this small river basin was devastated by a storm spate. In the main river bed, the destruction o f the riparian vegetation and the perturbation of the habitat led to a nearly complete loss of the benthic fauna and thus of the brown trout (Salmo trutta L.) populations. About 20 000 domestic fingerlings (5 c m mean length) were stocked during the spring of 1990 in the main rive r and its tributaries. In subsequent years, stocking practices were li mited to the head of the basin. Fishing was prohibited until March 199 3. Two sites were sampled five times from September 1989 to September 1993 for the evaluation of trout densities. In June 1993, 30 individua ls were sampled in the Abatesco to investigate allozyme polymorphism. Recolonization required at least two years. Although the exact influen ce of stocking practices was difficult to evaluate, we found that brow n trout restoration was mainly due to the populations of the tributari es, which had been less disturbed by the spate. The genetic analyses s howed that, in June 1993, 92% of the trout carried the wild allele LDH -5105 and 72% the endemic Corsican allele LDH-3*40, which is generall y only found in basin head populations. Thus, this study has shown tha t the wild population was primarily restored by the surviving individu als, particularly those from the tributaries that escaped the spate.