Wetenschap - 2 mei 2017

1.5 million dolphins and whales in North Sea

tekst:
Albert Sikkema

The North Sea houses 1.5 million cetaceans. This was announced by a European team, among whom are Wageningen researchers, that counted the number of whales, dolphins and porpoises in the North Sea.

Killer whales near the Shetland islands, photo: Hans Verdaat

In the summer of 2016, the European researchers counted the numbers of sea mammals in the European part of the Atlantic Ocean from boats and airplanes. Meike Scheidat of Wageningen Marine Research coordinated the count from airplanes; her colleagues Steve Geelhoed and Hans Verdaat were cruise leaders and responsible for one of the survey teams in the airplanes.

Dolphins
The researchers used a mathematical formula to translate the count to an estimate of the population. Their results were 467,000 porpoises, 468,000 short-beaked common dolphins, 372,000 striped dolphins and another 158,00 short-beaked common dolphins or striped dolphins. They also counted around 80 thousand rarer dolphins, such as common bottlenose dolphins, white-beaked dolphins and white-sided dolphins. In the ‘whale’ category, they counted 26,000 long-finned pilot whales, 14,000 sperm whales, 15,000 common minke whales and 18,000 fin whales in the North Sea.

Stable
It is the third time the researchers have counted sea mammals (not including seals) in the European Atlantic Ocean from Portugal to the north of Norway. The previous counts were done in 1994 and 2005. The researchers, led by the British professor Philip Hammond, did not discover any major fluctuations. They concluded that the number of porpoises, white-beaked dolphins and common minke whales has remained stable in the last 22 years. However, the researchers will require one more count to be able to make any substantiated statements about the other dolphins and whales.

Migration
Based on their previous counts, the researchers observed in 2005 that many porpoises had migrated from the north-west North Sea to its southern part. They have now observed that the population distribution has remained the same after 2005, with many porpoises having been counted in the south-west North Sea and near Denmark.

The research was performed by researchers from nine European countries that border on the North Sea, including England, Denmark, the Netherlands, France, Norway and Portugal. The research was funded by the governments of these nine countries. The researchers hope for a stable funding in the future in order to be able to continue the counts.


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