Dwarfs and cannibals in the Arctic: production of Arctic char (Salvelinus alpinus (L.)) at two trophic levels

Abstract

Due to extensive cannibalism, Arctic char (Salvelinus alpinus (L.)) often represent the two highest trophic levels in Arctic freshwater ecosystem where Arctic char often is the only freshwater fish present. There is a general lack of char stock size and production estimates from Arctic lakes although high catchability and late maturation of large piscivorous individuals raise considerable management challenges because large growing forms are a valued resource. Here, we use mark-recapture to estimate the biomass of both invertebrate feeding dwarfs (60–150 mm) and their cannibalistic conspecifics (>150 mm) in a small Arctic lake at Bear Island (74.5°N, 19.0°E; 11.3 ha; mean depth 1.8 m). Biomass was 10.1 and 2.0 kg ha−1 and production was 2.1 and 0.5 kg ha−1 yr−1 for dwarfs and cannibals, respectively. All the production of invertebrate feeding small char was removed by the cannibals. The low production of the Arctic lake ecosystems combined with high catchability of large piscivorous char indicates that these stocks may be particularly vulnerable to exploitation. We finally point out the similarity between Arctic and sub-arctic alpine populations of Arctic char in production and life-history parameters.