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Recruitment in the harbour seal (Phoca vitulina) population in the Dutch Wadden Sea
In: Netherlands Journal of Sea Research. Netherlands Institute for Sea Research (NIOZ): Groningen; Den Burg. ISSN 0077-7579; e-ISSN 1873-1406, meer
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| Abstract |
During 1974 to 1978 population dynamics of the harbour seal population in the Dutch Wadden Sea have been studied. Frequent aerial surveys provided data upon the size of the population. During boat trips information about the age composition was obtained by measuring track widths. These data have been used in a simulation model to calculate the birth rate and the initial juvenile mortality. It was found (1. that the initial juvenile mortality in the Dutch population is higher than that in Schleswig Holstein; (2. that pup production in the Dutch population is low compared to the population in Schleswig Holstein if the ratio adult females to males in the Dutch population is supposed to be equal to that in Schleswig Holstein, or that mortality amongst adult females in the Dutch population is higher than in Schleswig Holstein; (3.) that the number of subadults in the Dutch population is relatively high compared to a stable population (Schleswig Holstein) and that apparent1y immigration from elsewhere occurs; (4.) that the reproductive rate was higher or the juvenile mortality lower during 1974 to 1978 than in the preceding decennium. |
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