Ecology and trophic relationships of the fishes of gander lake, a large, deep, Oligotrophic Lake in Newfoundland, Canada

Gander Lake (surface area = 11320 ha, maximum depth = 288 in, mean depth = 105.4 m) is the third largest lake on the island of Newfoundland, Canada. Fish populations were sampled with Lundgren multiple-mesh experimental gillnets. As is characteristic of other water bodies in Newfoundland, fish diversity in Gander Lake was found to be low, with only six species encountered. The lake contains two morphs of Arctic charr, Salvelinus alpinus, a dark form and a pale form. Dark Arctic charr were found at benthic depths ranging from I to 280 in inclusive with highest catch rates occurring in the littoral zone. Pale Arctic charr were much less numerous than the dark form and were confined to profundal depths of 20 to 280 in, with most captures occurring at depths > 50 m. Anadromous Atlantic salmon parr, Salmo salar, were found mainly in the littoral zone and the maximum depth occupied was 20 m. Rainbow smelt, Osmerus mordax, were found down to a depth of 50 in and littoral and profundal occurrences were similar. Brook chart, Salvelinus fontinalis, were mainly littoral and the maximum depth occupied was 10 in. No pale Arctic charr or brook charr were captured in the pelagic zone. Catches in the pelagic zone for the remaining species were low in comparison to those of the benthic zone. There were no significant differences in length and age by lentic zone for any species. Dark Arctic charr were significantly larger and older than the pale form. There were marked differences in feeding habits between dark and pale Arctic charr. Stable isotope analysis depicted an Eltonian trophic pyramid with a greater number of fish species occupying successively lower trophic positions. Large piscivorus dark Arctic charr were at the apex of the benthic foodchain. There is evidence that benthic pathways account for most of total fish consumption and there is increased omnivory at lower trophic levels.