Tengiliður
Davíð Gíslason
Verkefnastjóri
davidg@matis.is
Samantekt:
The biology of Brown trout (Salmo trutta) and Arctic charr (Salvelinus alpinus) was studied in four Faroese lakes in late July – early August 2000. Relative density and condition of Brown trout were lowest in Leynavatn and highest in Saksunarvatn. Arctic charr only occurred in Leynavatn, where it outnumbered Brown trout by a factor of 2.7. For all fish populations, growth rates were slow, fish were small and maximum age of fish was low. The oldest fish in Toftavatn was 5+yr and the oldest fish in the study, in Saksunarvatn, was 9+yr. Asymptotic length was ca. 21 cm for arctic charr in Leynavatn and ca. 25 cm for Brown trout in both Leynavatn and Toftavatn, but for Brown trout in Eystara Mjáavatn andSaksunarvatn, no asymptote was observed. Small butsignificant differences in morphology were observedamong Brown trout populations with corresponding differences in diet. Brown trout in Toftavatn had a more forked caudal fin and the diet was more pelagic/epiben- thic than in the other lakes. In Leynavatn, Brown trout fed more on benthic diet and had a more curved snout than Brown trout in the other lakes, which may be signs of character displacement resulting from interspecific competition with Arctic charr. The Arctic charr in Leynavatn did not show signs of morphological or ecological polymorphism and their diet was both of benthic and planktonic origin. Genetic analyses of Arctic charr showed minor variation at most loci, high homozygosity and genotypic disequilibrium between three loci, indicating extensive inbreeding and random genetic drift in a small, isolated population. It is suggested that the restriction of Arctic charr to one natural lake in the Faroe Islands is primarily due to unfavourable water temperatures. Evidence suggests that the slow growth, small size and short lifespan of Arctic charr and Brown trout in Leynavatn may be due to interspecific competition between the two species along with relatively poor food conditions in the lake.