Spatiotemporal trends in white-beaked dolphin strandings along the North Sea coast from 1991–2017
The white-beaked dolphin (Lagenorhynchus albirostris) is an endemic species in the North Sea with an estimated population of around 36,000 individuals. Recently, concerns have been raised among conservationists regarding increasing water temperatures as a result of climate change, which could result in a decline in population numbers in certain areas of the white-beaked dolphin’s range. Here we use stranding frequencies of white-beaked dolphins as an indicator of distribution and investigate whether there have been spatiotemporal patterns and changes in stranding frequencies in the south western North Sea in the last 27 years (1991-2017). A total of 407 strandings was recorded and the distribution of stranded animals throughout this period revealed a higher density of animals in the southern countries in earlier years, with slightly increased densities in the north western area more recently. This could be a first indication of a change in habitat use and population distribution from southern to northern regions. A potential explanation for the observed shift is climate change and its effect on prey distribution and availability. This study highlights the potential of using stranding records as a way to collect high resolution spatiotemporal data, making this a valuable addition to surveys of live animals assessing species distribution and abundance. Additional research into metrics such as causes of mortality, life history and diet parameters (all of which are currently largely unknown for this species) would provide a welcome contribution to assess more detailed measures of the status of the population.