Are there variations in the distribution of Halichoerus grypus and Phoca vitulina populations in the Netherlands?

• Autor(a) principal: Abegão, Inês Pedroso
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33255
• topic: Halichoerus grypus; Phoca vitulina; Distribution; Phenology; Climate change; Anthropogenic activity

Common seals, Phoca vitulina, and grey seals, Halichoerus grypus, are sympatric pinnipeds indigenous in the Netherlands. Despite their differences at both morphological, ecological, and behavioral levels, both species are affected by a variety of threats such as fisheries, tourism/recreation, pollution, diseases and climate change. To evaluate potential changes in distribution, but also phenology of common and grey seals’ population that could be hypothetically related to such threats, an in-depth analysis of the live-stranding records from the Sealcentre Pieterburen between 1971 and 2020 was conducted. A total of 9 314 seals were studied, of which 7 298 were common seals and 2 016 grey seals. In order to explain possible changes in the distribution and seasonality of the species studied, a literature search was performed. The results obtained show an apparent change in both distribution and phenology for common and grey seals’ populations. Nevertheless, the results are obtained through the analysis of live-strandings which does not mean direct populational changes. Still, the growth in stranding records in the South of the Netherlands followed by a reduction in the North part of the country might indicate a relocation, and consequent change in distribution. Besides, common and grey seals pupping season seems to take place earlier according to the obtained results, assumed to be related with phenology changes. After the literature analysis, the changes in phenology were supported by several authors, however potential changes in distribution were difficult to defend. It was possible to affirm that the main reasons behind the observed changes are, as assumed, climate change and anthropogenic activity, more specifically, mainly associated with availability of food resources and higher disease prevalence, the last specially related to common seals.