Lepidurus arcticus (Crustacea : Notostraca); an unexpected prey of Arctic charr (Salvelinus alpinus) in a High Arctic river

The phyllopod Lepidurus arcticus, commonly called the arctic tadpole shrimp, is an important food item of both Arctic charr Salvelinus alpinus and brown trout Salmo trutta in lakes in Iceland and Scandinavia, especially at low fish densities. In the High Arctic, the tadpole shrimp is abundant in fishless localities, but absent or rare in most lakes where fish are present. We studied the diet of Arctic charr in the Straumsjøen watercourse on Spitsbergen, the main island of Svalbard. The outlet river is dry nine months of the year, and all Arctic charr present during summer have descended from the lake. We found that tadpole shrimp contributed substantially to the diet of charr in the outlet river, while it was not found in charr caught in the lake. Low fish density combined with low discharge after hatching of tadpole shrimp eggs may have favoured the co-occurrence of this lacustrine crustacean and Arctic charr in a running water locality. The potential effect of climate change on the occurrence of riverine tadpole shrimp is still uncertain. Retreat of glaciers and decreased turbidity may promote tadpole shrimp, but a predicted increase in precipitation may also have adverse impacts by increasing the risk of flushing tadpole shrimp out of the streams, and thus affecting the Arctic charr diet in running waters on Svalbard.