Skin lesions on endangered killer whales are getting worse, study says

Southern resident killer whales are increasingly suffering from skin diseases that leave large blotches on their distinctive black-and-white colouration, new research says.

The research, published Thursday in the journal PLOS One, analyzed photographs of more than 18,000 orca sightings from 2004 to 2016 in the Salish Sea, finding that the skin lesions have become "strikingly" more prevalent, posing another potential threat to a population already facing a range of challenges.

Co-author Stephen Raverty, a veterinary pathologist at the B.C. Animal Health Centre, said scientists who observed whales had previously noticed the unusual skin changes, but they had never before been assessed over time.

The study says that although the significance of the lesions was not clear, the possibility that they related to decreasing body condition and immunity in an endangered population was a concern.

It says scientists hypothesized the lesions could be an infectious agent and an indicator of the whales' declining ability to fend off illness.

The exact underlying cause of these skin issues wasn't clear, said Raverty, but they could result from human activities.

"We know that for sure there are consequences related to increasing vessel traffic, contaminant loads, increased noise in the marine environment, and lack of prey are sort of the major components that are recognized to impact southern resident killer whale health," said Raverty.

Joseph Gaydos, chief scientist for the University of California, Davis, school of veterinary medicine and the study's lead author, said in a statement that before looking at the data they had no idea the prevalence of skin lesions was increasing so dramatically.

"It's worrisome. Now we need to try and isolate the potential infectious agent," said Gaydos.

The study involved 141 whales, 99 per cent of which had evidence of skin lesions at some point in the study.

The most common types of lesions were "grey patches" observed in 27 per cent of sightings, followed by "grey targets" seen in 24 per cent of sightings.

Raverty said the study was a step forward in evaluating the health of whales via "non-invasive" assessment.

"[It]helps inform us in terms of whether these changes may be indicative of something that's going on systemically and might impact the health of the animals," said Raverty.

Another co-author, Martin Haulena, head veterinarian with the Vancouver Aquarium, said the study can help scientists recommend conservation strategies.

As a highly contaminated group of animals, killer whales are affected by the conservation of salmon species, habitat and noise, he said.

"Healthy environment, minimal disturbance, those things are very important for the recovery of the whales," said Haulena.

This story was produced with the financial assistance of the Meta-Canadian Press News Fellowship, which is not involved in the editorial process.