Comments to a polar bear population model

Larsen, T. & Ugland, K. I. (Polar Research 2 n.s., 117–118) note correctly that a Leslie matrix model treats cubs and females as independent units which is not the case lor polar bears. Population projections using the Leslie model with hunting mortalities added are instructive first approximations in evaluations of field data, however, and are recommended as exercises also for polar bear biologists. An APL programme for such projections is available.     

Size, age and spawning frequency of landlocked arctic charr Salvelinus alpinus (L.) in Svartvatnet, Svalbard

This contribution reports the analysis of a sample of landlocked arctic charr collected with gillnets in Svartvatnet, Svalbard, 1964. This is the first scientific sample from a landlocked charr population from Svalbard. We found a very prominent modal group of large, old and sexually adult fish of both sexes. Their length ranged from 15 to 62 cm, but 92% of the fish were longer than 40 cm and 62% of them fell in the 45 to 54 cm interval. The age range was 7 to 31 years, but 93% were 14 years or older and represented 18 year-classes. The length-at-age of the charr seemed to increase steadily until they reached the size and age of the modal group. The growth rate decreased sharply after that. The mortality rates within the age span of the modal group seemed to be low. The ages at first spawning for most of the charr in the sample were between 7 and 9 years and spawning cycles of two years were indicated.