Utrecht University: Stranded humpback was young, emaciated female

On Tuesday, July 5th, Defence staff found a dead humpback whale off the coast of Vlieland. Based on injuries to the tail, researchers could determine that it was the same humpback that had been swimming off our coast since the end of May. Marine biologist Lonneke IJsseldijk and colleagues from Utrecht University are investigating the cause of death and the state of health.

Poor health
On 23 May, a humpback whale was seen off the coast of Zeeland. The animal showed up a few more times, the last time on 23 June in Marsdiep (a sea channel between Den Helder and Texel). Humpback whales are about 4 meters long when they are born and can survive without a mother when they are 8 meters long. The first investigations showed that it was a young female of 6.5 meters, so she must have been independent for a short time. She was in poor health, skinny and suffered from severe skin inflammation. Parasites (whale lice, Cyamidae) were found in several places on the skin layer. In addition, dehydration symptoms were discovered, which were probably caused by a lack of high quality, moist food.

No clear cause of death yet
At the moment, a number of causes of death can be ruled out on the basis of external factors. No damage was found on the skin indicating asphyxiation by ropes or nets. In the large internal organs, no indications of disease were found – microscopic examination should further reveal the absence of inflammation. Additional microbiological examination will also be carried out. A piece of plastic was found in the intestines, but this also had no influence on the cause of death. Wageningen Marine Research is investigating the rest of the intestinal contents. Finally, the researchers discovered some broken bones that may have occurred before or after the death (during stranding).

Humpback whales are being observed more and more often in the southern North Sea; they can survive very well in shallow water. However, it is rather rare for them to strand on our coast: the last stranding of a humpback was in 2012. Before that, there were only six previous reports.

Lonneke IJsseldijk