Population structure of the otter, Lutra lutra. Parameters and model for a Central European region

A sample of 225 dead otters - mostly road-kills - was collected from 1980 to 1995 in Upper Lusatia ("Oberlausitz", Germany). All otter carcasses were examined for signs of reproduction and were aged according to incremental cementum lines. The data obtained were combined with field observations of cubs to endeavour the modelling of real population parameters. In the Upper Lusatia region the mean litter size of the otter (2.7) and the proportion of early losses of cubs (24%) appeared to be at a normal level compared to different data from the European area. The proportion of adult non-breeding females amounted to 40%. Among otter carcasses the males predominated especially in younger age classes. In Upper Lusatia, otters live to a very old age, up to 16 years, and the sample shows a high fraction of older animals. By using the obtained parameters a population model for the otter in the Upper Lusatia region was developed. The age pyramid of this model is relatively stretched with a female-biased sex ratio among the adults, thus compensating for the low proportion of breeding females. Mortality is very high during the first year, but very few otters die in middle ages of life. Except for juveniles the survivalship curve shows a convex trend typical for longlived large mammals.