Bottlenose dolphins in the Netherlands come from two sides: across the North Sea and through the English Channel

Abstract

On 19 July 2019 an estimated 20 bottlenose dolphins (Tursiops truncatus) were observed in the Marsdiep, a tidal inlet connecting the North Sea and the Dutch Wadden Sea, between Den Helder and the island of Texel. Photographs and video recordings were made and nine individuals were matched with known dolphins from the Moray Firth, NE Scotland. These are the first matches of this east coast of Scotland population outside the UK and Ireland. Subsequent observations of individuals from this group show that at least some of the animals have returned to Scottish waters, while others were photographed in Danish waters. Furthermore, we report on a photo identification match of a solitary bottlenose dolphin between France and the Netherlands. These matches suggest that bottlenose dolphins, in the Netherlands, originate from two different genetically distinct populations: ‘Coastal South’ and ‘Coastal North’. This evidence of previously unknown long-range movements may have important implications for the conservation and management of this species in European waters.

Spatiotemporal Trends Spanning Three Decades Show Toxic Levels of Chemical Contaminants in Marine Mammals

“…It is likely that several individuals will have foraged in waters at large distances from their stranding location and so pollutant levels are likely to be reflective of the wider regions. 69 We expect our results are representative of marine mammals that inhabit the seas surrounding Great Britain; however, there may be local variations. For example, there are large numbers of common dolphins in the southwest of the UK; however, they are a wide ranging and fast-moving species and little is known about the movement of individual pods; therefore, spatial trends should be interpreted with caution.…”

“…It is important to consider that the spatial distribution of pollutant concentrations can also vary according to animal movement and carcass drift, causing animals to accrue pollutants in a location different from where they strand. It is likely that several individuals will have foraged in waters at large distances from their stranding location and so pollutant levels are likely to be reflective of the wider regions . We expect our results are representative of marine mammals that inhabit the seas surrounding Great Britain; however, there may be local variations.…”

Kaders en voorwaarden voor het laten liggen van walviskadavers in het Waddengebied

“…Nu de zee weer opwarmt, lijken de witsnuitdolfijnen zich weer terug te trekken naar het noorden en maakt de gewone dolfijn vanuit het zuiden een voorzichtige come-back, in tegenstelling tot de periode 1930-1965 nu samen met de gestreepte dolfijn die dus een nieuwkomer is (Figuur 14). Tuimelaars blijven vooralsnog zeldzaam, maar af en toe stranden in Nederland nog wel dieren, die afkomstig blijken uit zowel het noordwesten (Schotland) als uit het zuiden (Frankrijk-Ierland (Hoekendijk et al 2021).…”

“…Wat ze hier eten is nog niet duidelijk. Maagonderzoek aan een klein aantal gestrande dieren laat vooralsnog een weinig eenduidig beeld zien (IJsseldijk et al, 2020;Hoekendijk et al 2021), dus biologisch onderzoek aan meer dieren is gewenst.…”