Population structure, biomass, and diet of landlocked Arctic charr (Salvelinus alpinus) in a small, shallow High Arctic lake

Although landlocked Arctic charr, Salvelinus alpinus, occur in a large number of High Arctic lakes and often as the only fish species, knowledge of densities and resource use is limited. An allopatric landlocked population of Arctic charr in the 1.47 ha Lake Nordre Borgdam on Svalbard (78°3′N, 13°5′E) was studied during the period 1998–2004. Population abundance was estimated by mark–recapture in July–August 2001. The population was dominated by small individuals with lengths below 16 cm. In 2001, the total number of charr in the length-class 6.0–15.9 cm corresponded to 1,920 individuals/ha or 20.7 kg ha−1. They were mostly feeding on chironomid and trichopteran larvae. The few larger charr seem to feed mainly on smaller conspecifics, and these cannibals probably control the population structure and the abundance of smaller fish. Due to low total number of prey fish in the lake, few individuals are likely to become piscivores.