By Jeannette Bylov, AAU Communication og Public Affairs

Climate change means that species disappear from the land, air, and sea, so it is not every day that researchers can document a new breeding whale species in Denmark – especially not a large one weighing up to 350 kg.

It involves the white-nosed dolphin, which can now safely be said to breed in inner Danish waters. White-nosed dolphins are not uncommon in Danish waters, but it has been assumed until now that the porpoise is the only whale species that breeds in inner Danish waters. It is known that the white-nosed dolphin breeds in the North Sea. Every year, there are reports of sightings of white-nosed dolphins.

"The white-nosed dolphin is the most frequently stranded whale species after the porpoise, but we have not previously been able to document that they actually breed in inner Danish waters. The white-nosed dolphin is protected under the Habitat Directive, and it would be a good idea to begin monitoring populations of white-nosed dolphins in Danish waters, just as we do with porpoises," says Sussie Pagh, a biologist and senior researcher at the Department of Chemistry and Bioscience at Aalborg University.

Great analysis work behind the discovery

There is a lot of work involved in reviewing old autopsy reports and records to discover that the white-nosed dolphin breeds in inner Danish waters. In the summer of 2023, a white-nosed dolphin was collected by the Danish Nature Agency Central Zealand in Nekselø Bay, north of Havnsø. The dolphin was brought for autopsy at Aalborg University, which at the time was responsible for marine mammal autopsies for the Environmental Protection Agency as part of the 'Preparedness for stranded marine mammals in Denmark.' When the white-nosed dolphin was opened, an almost full-term fetus weighing 15 kg appeared.

A lone swallow makes no summer. Therefore, it took more documentation than a single full-term fetus for the researchers to conclude that white-beaked dolphins breed in inland Danish waters.

"We started reviewing autopsy reports and reported observations from several years back in time. The many findings confirmed our theory that the white-nosed dolphin breeds in several places in inner Danish waters," explains Charlotte Bie Tøstesen, natural history manager at the Fisheries and Maritime Museum.

The research group could specifically ascertain that there were eight instances where white-nosed dolphins were found either with a fetus or were lactating. In one instance, a newborn calf with milk in its stomach washed ashore near Strandby near Frederikshavn in 2017, in addition to a live white-nosed dolphin with a calf spotted at Sletterhage lighthouse in 2011.

"The many findings over time of white-nosed dolphin fetuses, lactating white-nosed dolphins, and a single mother with a live calf mean that we can now conclude that the white-nosed dolphin not only breeds in the North Sea near Denmark but also in the inner Danish waters," says Sussie Pagh, a biologist and senior researcher from AAU.

Behind the discovery is a team of whale researchers from various institutions in Denmark, including researchers at Aalborg University, Aarhus University and the Fisheries and Maritime Museum in Esbjerg, who set out to review the archives to investigate how many breeding white-nosed dolphins have been documented in inner Danish waters over the past 20 years.

Sources:

• Coasts 2024, 4(2), 226-34; https://doi.org/10.3390/coasts4020013
• Carl Christian Kinze, Dansk Pattedyr Atlas, Handbook of the Mammals of Europe
• White-Beaked Dolphin Lagenorhynchus albirostris (Gray, 1846), Anders Galatius, Carl C. Kinze & Peter G. H. Evans.