The return of the harbour porpoise (Phocoena phocoena) in Dutch coastal waters
Camphuysen, K.C.J. (2004). The return of the harbour porpoise (Phocoena phocoena) in Dutch coastal waters. Lutra 47(2): 113-122
In: Rijksmuseum voor Natuurlijke Historie Lutra (Leiden). Brill: Leiden. ISSN 0024-7634, more
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| Keywords |
Phocoena phocoena (Linnaeus, 1758) [WoRMS]
Marine/Coastal |
| Author keywords |
harbour porpoise, Phocoena phocoena, sightings, The Netherlands, population trends, historical decline, distribution shift |
| Abstract |
The harbour porpoise (Phocoena phocoena) became virtually extinct in Dutch coastal waters in the early 1960s. A systematic method to record seabird passage along the coast became established in the early 1970s and was used ever since. These observations allowed a reconstruction of the return of the elusive harbour porpoise in Dutch coastal waters. A small, but gradually increasing number of sightings in the mid-1980s to early 1990s was followed by a proportional rate of increase of 41% per annum over the last 15 years. At first, only full-grown animals were seen and the occurrence was virtually restricted to mid-winter. In later years, numbers sharply increased in winter, and more and more animals were seen also in summer and autumn, including mother-calf combinations. Both the historic decline and the recent increase are concurrent with similar trends in strandings and at sea survey data. Unambiguous explanations for the initial decline have never been given and it is equally difficult to fully understand the come-back. There is evidence, however, that distributional shifts rather than population fluctuations underlie the trends observed. The re-distribution of harbour porpoises in the North Sea may have been triggered by local reductions or shifts in principal prey availability. |
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