A Joint Effort to Explain Mass Seal Deaths in New England

More than 1400 seal deaths have been reported along the East Coast in recent months, spanning Virginia to Canada, with the largest cluster found in the New England area. Scientists in the region suspect the cause of the mass deaths to be distemper, which is known to circulate among seal populations. The New Hampshire Veterinary Diagnostic Lab at the University of New Hampshire and Seacoast Science Center Marine Mammal Rescue have joined forces to determine the cause definitively.

While the New Hampshire Veterinary Diagnostic Lab’s primary responsibility is to agricultural veterinary clients, it has expanded into work with wildlife species over the past decade in an effort to better assist in the surveillance and management of diverse wildlife populations.

“This work supports our emphasis on the concept of One Health, recognizing that human, wild, and domestic animal, and ecosystem health are interdependent,” said Inga Sidor, DVM, MS, senior veterinary pathologist at the lab. “This partnership with Seacoast Science Center formalizes our involvement with monitoring health and disease in Gulf of Maine marine mammal species.”

In late November, the New Hampshire Veterinary Diagnostic Lab took on its first case after Marine Mammal Rescue received a report of a seal on the beach. The young male harp seal was alive but unresponsive. After removing it from the beach to conduct further health assessments, the seal died.

The seal was then examined and tested for phocine distemper virus, but preliminary results were negative for viral infection, suggesting that something else may have caused the seal’s death.

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“It was an unusually robust juvenile animal compared to the more typical very skinny late-fall pups we see who are having trouble making a living in the harsh environment of the ocean,” Dr. Sidor explained. “An animal in good body condition immediately suggests a different set of causes. If we can rule out infection, acute toxicity as the result of harmful algal blooms might also be considered.”

The negative test result leads the Seacoast Science Center Marine Mammal Rescue to believe the virus may have run its course. According to the National Oceanic and Atmospheric Administration, the peak months of the die-off linked to distemper were August and September 2018.

"As the temperature drops, the virus can't duplicate as quickly, so it can't spread as quickly,” Seacoast Science Center Marine Mammal Rescue manager Ashley Stokes told a local public radio station.

However, even with the threat of distemper dwindling, Stokes remains excited about how the new partnership will positively impact marine life in the area by providing year-round necropsies of protected marine mammals. “Prior to the partnership, specimens were sent to the New England Aquarium facility in Quincy (NEAq), Massachusetts,” she said. “Having access to [New Hampshire Veterinary Diagnostic Lab at the University of New Hampshire] will ensure quick and accurate diagnostics when NEAq’s facility is at capacity or unable to take carcasses during sea turtle rescue season.”

“If there's something we can do to prevent it or if we start to see a trend, it just helps show us what's going on in the grand scheme of those animals rather than just simply taking measurements and disposing of them,” she added.