| Summary: | Between 1998 and 2007, 2063 cetaceans were found stranded in the Netherlands, representing at least 14 species. Two species, humpback whale (Megaptera novaeangliae) and Blainville's beaked whale (Mesoplodon densirostris), are additions to the Dutch list. Apart from the first humpback whales, relatively many balaenopterid whales were found in comparison with previous decades. Range extension of recovering populations may explain part of this trend. However, the decline in strandings frequency in sperm whales (Physeter macrocephalus), another species with a slowly recovering Atlantic population but with a distinct peak in strandings in the 1990s, suggests that the factors underlying these changes are complex. During the 20th century, the strandings frequency of some dolphin species regularly occurring in the North Sea has changed markedly. Bottlenose dolphins (Tursiops truncatus) disappeared in the 1960s, common dolphins (Delphinus delphis) were fairly numerous during some decades in the mid-20th century, and white-beaked dolphins (Lagenorhynchus albirostris) became abundant and virtually replaced bottlenose dolphins in the strandings records since the 1970s. Numbers of stranded harbour porpoises (Phocoena phocoena) continued to increase over the years. All individual cases other than harbour porpoises are listed in this paper, reporting species, (late, locality, reporter, sex, total length (TL), collected remains, and remarks. A total of 1968 reports of stranded harbour porpoises were received, ranging from 59 in 1998 to 539 in 2006. It is estimated that along the North Sea coast at least 19% more porpoises were washed ashore than were actually recorded. On the Wadden Sea islands, this discrepancy is estimated as at least 30%. The mean length of porpoises declined gradually with time and the sex ratio was male-biased in all subregions. From measurements (TL) it is concluded that circa 72% were juveniles, with small proportions of adults (15.5%; unsexed and male male animals of TL > 150cm, female female animals ...
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