Young Australian fur seals are losing the thick coats that keep them warm in chilly waters.
The condition disproportionately affects 1-to-3-year-old females on Lady Julia Percy Island near Tasmania, and seems to be causing their population to drop.
“Large numbers of animals get it, and it’s detrimental to their health,” said Michael Lynch, a veterinarian at the Melbourne Zoo and lead author of the study published in the April issue of the Journal of Mammalogy.
Australian fur seals were nearly hunted to extinction in the 1800s for their coats. They were slow to recover until they received full protection in 1975. Since then, the population has about doubled, says Roger Kirkwood, a research scientist at Phillip Island Nature Park near Melbourne, Australia and a co-author of the study.
These increases continued until 2007, when census data showed a slight decrease in the fur seal colony at Julia Percy Island, where almost all recorded cases of hair loss have occurred.
Unlike elephant seals, which are insulated against cold by enormous rolls of blubber, Australian fur seals rely on thick fur coats. Fur loss forces them to spend more energy maintaining body temperature, and leaves less energy for other activities.
Scientists first noticed the condition, which primarily affects the head and back, in 1989 at a small breeding colony southeast of Julia Percy Island. In 2004, Kirkwood started noticing more severe cases at Julia Percy. The island is home to about 30,000 seals, or about one quarter of Australia’s fur seal population.
Between 2007 and 2010, Lynch and his colleagues took skin, hair and blood samples from Julia Percy’s seals. They found that about half of young females — some 25 percent of the colony’s entire population — had the condition, which peaked during spring and summer. Only several adult females and a few young males were afflicted. Adult males were unaffected.
Images taken with a thermal camera revealed that affected seals couldn’t control heat loss from balding areas.
The researchers have ruled out common culprits like fungal infections or mange. They’re now trying to narrow down possible non-infectious causes like allergies, genetic disorders, or environmental toxins. It’s still very much a work in progress, says Lynch.
“Depending on the genetic diversity of this population, a genetic concern remains on the list of possible contributors to this condition,” said Judy St. Leger, director of pathology and research at SeaWorld San Diego, who was not involved in this study. But she also notes that hormonal imbalances or heavy metals like selenium might play a role.
“I would still count mites and mange as a strong possibility, as they can be hard to find deep in the hair follicles,” said Todd Schmitt, senior staff veterinarian at SeaWorld San Diego who wasn’t involved in the study. “It’s likely multifactorial and coincides with the seasonal molt and maturation of the animal’s immune system.”
That it’s mostly the younger animals with hair loss means they could be growing out of the condition as their immune systems mature, says Schmitt.
“Until they complete and publish the follow-up work, the evaluation leaves a lot of questions about what’s happening with the individual animals,” said St. Leger. But, she adds that “folks in Australia are doing some very good population assessments. These are critical to keeping an eye on the changing environment.”
“Until you understand what the cause is, you don’t know what the implications are for the rest of the population,” said Lynch. He’d like to do more detailed tests, including ones for potential allergies, but his budget is tapped out for now. Lynch is currently applying for grants to continue his analysis of the hair and blood samples.
Image: Left-Australian fur seal with hair loss condition. Courtesy of Michael Lynch. Right-Thermal image of the same seal, showing more heat loss in balding area. Courtesy of Michael Lynch.
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