The cause of an unusual number of dead and dying otters winding up on Homer beaches remains unexplained, but preliminary results suggest toxins from harmful algal blooms and stress from bacterial infections might be contributing to the deaths. Infections also might cause otters to forage in shallower waters on less-nutritious prey like blue mussels.
“The otters are getting a double whammy,” said Deborah Boege-Tobin, a biology professor at Kachemak Bay Campus, Kenai Peninsula College. “We don’t know for sure, but that’s what we’re looking into.”
To add to the mystery, some dying otters appear healthy with lots of muscle and body fat, but act paralyzed or seize just before death, she said.
Boege-Tobin heads the Homer branch of the Alaska Wildlife Response Network. Since August, about 25 volunteers have collected 114 dead or dying otters on Homer beaches. One otter, a pup, was saved on Sept. 18. Named Kesuk, he is being rehabilitated at the Alaska SeaLife Center in Seward. His mother had to be euthanized.
Samples were taken of the mother, and her body was sent to a veterinary pathologist for a necropsy, but the cause of death has not yet been reported, said Tara Reimer, president and chief executive officer of the SeaLife Center.
Throughout Alaska, 190 otters have been collected this year, most of them dead. Sick otters are monitored by volunteers and, if they cannot be rehabilitated, are euthanized by veterinarians, including vets from Homer Veterinary Clinic.
Some of the Wildlife Response Network volunteers come from the Kachemak Bay Campus Semester by the Bay program, which brings students from the Lower 48 to study marine biology. Boege-Tobin, who also runs the program, has been giving her students a crash course in otter research.
That can include the sometimes gross job of poking around in a bloated otter carcass to take teeth samples, like student Natalie Hunter of Wilmington, N.C., did on a chilly Friday afternoon in late October. Hunter also recorded information like length and sex and, if the body was fresh enough, collected the otter. On Oct. 30, Hunter and other volunteers collected two dead otters and studied a third. That’s typical of recoveries volunteers have done.
“At one point we were getting three to 11 otters a day,” Boege-Tobin said.
Homer volunteers have been so diligent in studying dead otters and monitoring live otters that last week the Alaska SeaLife Center awarded its Planet Blue Partnership Award for 2015 to the Homer volunteers and to the Homer Veterinary Clinic.
Kachemak Bay has about 6,000 sea otters. The dead otters washing up on north-shore beaches could have drifted in from other areas. Some otters have been emaciated while others have been otherwise healthy with good body fat. One otter was shot. Some show evidence of valvular endocarditis, a bacterial infection that can damage the heart. Valvular endocarditis was seen earlier this century in a similar die-off in Kachemak Bay. The exact cause of death remains unknown for many otters, the SeaLife Center and the U.S. Fish and Wildlife Service said in a press release last month.
“A team of experts from the U.S. Fish and Wildlife Service, the Alaska SeaLife Center, Alaska Veterinary Pathology Services and the U.S. Geological Survey National Wildlife Health Center are working to understand what has caused the spike in sea otter deaths and potential significance to the population,” the press release said.
A small sample of 16 otters tested positive for toxins from harmful algal blooms. Seven otters had domoic acid, a toxin produced by Pseudo-nitzschia, a plankton seen in blooms this summer in Kachemak Bay. Eight otters had toxins from Alexandrium plankton, the same plankton that causes paralytic shellfish poisoning, or PSP. One had both domoic acid and PSP. One otter had a domoic acid count of 594 nanograms per milliliter.
The U.S. Food and Drug Administration considers domoic acid concentrations of 20 nanograms per milliliter to be unsafe if seen in shellfish. Tests done of plankton samples in Kachemak Bay showed trace amounts of domoic acid.
However, since otters eat 40 percent of their weight daily, Boege-Tobin cautioned that biotoxin levels in otters can’t be compared to that in shellfish or translated into levels that would be toxic to people. That some otters tested positive for domoic acid or PSP also does not mean biotoxins caused the recent die-off of all the otters. Even for the otters that tested positive for toxins, the toxins may not be the direct cause of death. One otter that tested positive for PSP was the one that had been shot.
“We don’t have enough evidence to say it’s causing this die-off,” Boege-Tobin said. “But yes, the food web here does have these toxins in it and, yes, there is HAB (harmful algal bloom) toxin exposure showing up in the small sub-set of tested dead. … It certainly doesn’t explain the whole situation.”
PSP often shows up in blooms in isolated bays and covers. Some mussels and oysters tested positive for PSP in Halibut Cove and Peterson Bay this summer. Not enough is known about foraging behavior of otters in Kachemak Bay, and because the tides and currents washed up many dead otters, “We don’t really know where they got contaminated,” Boege-Tobin said.
To help answer that question, Boege-Tobin said researchers hope to do behaviorial studies in otter foraging habits next summer.
Meanwhile, Kesuk, the otter who lost its mother, has grown healthy enough that it can swim with another orphaned otter, Atka. Atka also was recovered from Homer, but on July 1, before the spike in otter deaths. A third sea otter pup was rescued Oct. 25 from Nikiski and also is at the SeaLife Center. Still unnamed, it remains in quarantine, Riemer said.
Unlike seal pups, which separate from their mothers at a young age, sea otters stay with their mothers for a longer time and cannot be rehabilitated and released to the wild. Kesuk and Atka eventually will be placed in a zoo or aquarium.