It was a bacterial infection, not the recurrence of a deadly plague in 2002 that killed nearly 4,000 seals, which has resulted in over 100 of the animals washing up on the beaches of the island of Anholt over the last two weeks.
Cause of death unsealed
Mariann Chriéll, a veterinarian at DTU, told Jyllands-Posten that her team have dissected four of the seals and revealed that a bacterial infection has caused weak individuals to develop an acute and eventually terminal pneumonia.
"The seals get so much blood in their lungs and coming out of their noses that it almost flows over," she said.
No second plague
As gruesome as it may sound, a seal plague similar to the one 12 years ago would be much more alarming.
"This bacteria primarily attacks weakened and sensitive animals, but all seals can contract the plague," said Chriéll.
"And it's been so long since the last outbreak that very few remain immune."
Seals are particularly vulnerable to infection at this time of year because they tend to gather on land and lie close to one another.