The perfect storm: can sperm whale (Physeter macrocephalus) strandings in the North Sea be linked to storm activity?
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In early 2016, 30 male sperm whales (Physeter macrocephalus) stranded along North Sea coasts. Sperm whale mass strandings in the North Sea area have occurred several times over the past century and are relatively well documented. Most strandings occur when sperm whales migrate south from the Norwegian Sea, and enter the shallow North Sea by accident. There are multiple theories regarding the cause of why sperm whales sometimes take the wrong turn into the North Sea ‘trap’. One hypothesis focuses on a positive association between higher temperatures and increased probability of sperm whale strandings. Another hypothesis focuses on a link between solar storms and disturbances in Earth’s magnetic field, and sperm whale strandings. In this study, a third hypothesis is investigated: a possible link between the occurrence of (severe) storms and sperm whale strandings. It is important to gain additional insight in what drives North Sea sperm whale strandings, since climate change will affect sea surface temperature and will also lead to increased storm frequency and activity. This might lead to a further increase of the frequency of sperm whale stranding events in the future. The storm activity results indicate that wind speed, measured off southwest Norway, is not directly related to the early 2016 sperm whale stranding event. Historical records of storm activity on Iceland and in the North Sea area also show no good correlation with the historical North Sea stranding record, indicating that there is no direct link between (severe) storm activity and sperm whale strandings. Other parameters that have been investigated on short time scales, such as chlorophyll levels, SST and sea surface currents, are also excluded as major drivers behind the early 2016 event. For now, the hypothesis regarding the solar storms and the corresponding disturbances in Earth’s geomagnetic field seems to be the most likely.