In one more sign that North Atlantic right whales are struggling, a new study finds sky-high levels of stress in animals that have been caught in fishing nets.

Researchers determined the stress hormone levels of more than 100 North Atlantic right whales over a 15-year period by examining their feces. Sometimes guided by sniffing dogs, researchers followed the animals, collecting waste samples that they then analyzed in their lab at the New England Aquarium.

Results from the feces of 113 seemingly healthy whales helped establish a baseline of stress hormone levels, which had never before been known for the species. “We have a good idea of what normal is now,” said Rosalind Rolland, who developed the research technique and is the lead author of the study published in the journal Endangered Species Research.