Landlocked Arctic charr (Salvelinus alpinus) population structure and lake morphometry in Greenland -: is there a connection?

Landlocked Arctic charr (Salvelinus alphinus) populations in sub-Arctic and Arctic Greenland lakes were sampled with multi-mesh-sized survey gillnets. The study covered a range of small shallow lakes (0.01 km(2) maximum depth <3.3 m) to large deep lakes (43 km(2), maximum depth >200 In). Arctic charr were found in one to three different forms in lakes with maximum depths >3 m. A dwarf form occurred in all lakes inhabited by Arctic charr and was the only form in lakes with maximum depths <8 m. In deeper lakes with maximum depths,20 m and a surface area <0.5 km(2) larger charr were found, although in low numbers, the length-frequency distribution being unimodal with a tail towards large sizes. In lakes with a maximum depth >20 m, large-sized charr were more abundant, and the length-frequency distribution of the population was bimodal, with a first mode around 10-12 cm and a second mode around 2637 cm. In a single large and deep lake, a distinct medium-sized pelagic zooplankton-eating charr form occurred. Maximum size of individual charr was significantly positively correlated with lake maximum depth and volume, and the mean size of large-sized charr was significantly positively correlated with lake volume. Our study indicates that the charr population structure became more complex with increasing lake size. Moreover, the population structure seemed to be influenced by lake-water transparency and the presence or absence of three-spined stickleback (Gasterosteus aculeatus).