The number of harbor porpoises in the Dutch part of the North Sea increased more than sevenfold between 1991 and 2019. However, the numbers near the coast are falling. This is the conclusion of the Central Bureau of Statistics (CBS) from new analyzes carried out in collaboration with Wageningen Marine Research (WMR).
The results were published in the Kompendium für das Lebensumfeld, a collaboration between Statistics Netherlands and Wageningen University. Since November 3rd of this year the harbor porpoise is no longer on the Red List of Endangered Mammals in the Netherlands and its survival is therefore no longer threatened.
The harbor porpoise was a common species in the Dutch part of the North Sea for centuries. From 1940 the number fell sharply. The population development of harbor porpoises shows a strong upward trend from 1991 to 2019. In 2019 the population was more than seven times as many animals as in 1991.
The increase in the number of harbor porpoises in the Dutch part of the North Sea is related to a shift of the animals from the northern North Sea to the south. The number of harbor porpoises varies from 26,000 (October-November 2010) to 86,000 (March 2011) within a year. From 2014 the number of harbor porpoises near the coast, no more than a few hundred meters from land, will decrease.
With the increase in the number of porpoises in the coastal zone, the number of stranding dead porpoises has increased sharply since 1991. This number rose from a few decades at most in the early 1990s to a few hundred per year from 2004 onwards. The largest number of strandings since registration began was 962 in 2011 and 980 in 2012. After this peak, this number fell again. This is in line with the lower numbers observed near the coast.
Known causes of death for stranded porpoises include drowning in fishing gear, infectious diseases, starvation, collisions with propellers, and attacks by seals