Dead basking shark found on Danish beach near Ålbæk leaves scientists searching for cause of death

Discovery on the beach

A female basking shark, the second-largest living shark species, was found dead on a beach near the Danish town of Ålbæk, close to Skagen, on Saturday, 8 August. The shark had first been observed in shallow waters near the shore on 6 August, where it attracted attention from tourists and residents over several days as it swam in search of food. Its body was discovered on the beach approximately one kilometre north of the harbour in Ålbæk. The Nordsøen Oceanarium documented the transport of the large carcass using a front-end loader and shared footage on Facebook.

Sources give slightly different measurements for the animal: three articles report a length of 4.7 metres, while two others give 4.85 metres. Its weight was approximately 500 kilograms. The shark was identified as a young female, estimated at 10 to 15 years old. Basking sharks can live up to 50 years and exceed 8 metres in length, making this individual a relatively young specimen.

Necropsy findings

On Wednesday, 12 August, a team of eight specialists from four Danish institutions conducted a detailed necropsy at the Nordsøen Oceanarium in Hirtshals. The institutions involved were the Statens Naturhistoriske Museum, Kattegatcentret, Museum Sønderjylland, and Nordsøen Oceanarium. The procedure was led by Kristina Ydesen, lead biologist at the Nordsøen Oceanarium, and was broadcast live on social media.

The examination found the shark in an early stage of decomposition, allowing for a more thorough investigation than is typically possible with stranded marine animals, which are often in advanced decay. Researchers reported that the animal appeared healthy: no serious injuries, no signs of starvation, and no plastic in its digestive system. The stomach contained remnants of plankton and small crustaceans, indicating the shark had eaten approximately one day before death. The heart weighed 1.5 kilograms and the liver 75 kilograms, with liver mass representing about 15 percent of body weight.

Body weight500

Liver75

Heart1.5

Body weight

500 kg

Liver

75 kg

Heart

1.5 kg

Data from the article text

Parasites resembling long, thin spaghetti were found in the intestines, but researchers did not consider them numerous enough to have caused death.

“We found parasites in the shark's intestines, long, spaghetti-like worms. However, not so many as to believe that this affected the shark's health or that it was sick.”

Ongoing investigation

Scientists have collected tissue samples for laboratory analysis. The shark's head will undergo a CT scan at the University Hospital in Aarhus to check for hidden infections or diseases not detected during the necropsy.

“We are very curious, so we hope to get answers.”

Ydesen also reflected on the rarity of the opportunity.

“Perhaps in my entire career as a biologist I will only have this one chance to perform a necropsy on a basking shark. For this reason, it was a completely unique experience.”

A rare visitor

Basking sharks typically inhabit the open oceans, including the Atlantic and Pacific, and only sporadically appear in Danish waters. Since 2000, approximately ten such cases have been documented in the region. The last comparable event occurred in 2015, when a fisherman in the Kattegat accidentally caught a 4-metre basking shark in his nets. The species feeds primarily on plankton and does not prey on humans, despite its enormous size.