by Todd McLeish
After University of Alaska students Amy Kirkham and Quinsey Jorgensen joined us, the real work began. Kirkham used a pair of pliers to remove one of the otter’s premolar teeth for later use in accurately determining the age of the animal; I later learned that Otter FW14026 was four years old. Then she pulled out a handful of the animal’s whiskers for future analysis of stable isotopes that provide an indication of what the otter had been eating in recent weeks. At the same time, Worman used a scalpel to make an incision down the length of the otter from throat to tail. She and Renay had prepared a dozen scalpels in advance knowing that the animal’s thick fur would rapidly dull the blades. As Jorgensen took notes and stored tissue samples, the rest of the group spent the next thirty minutes completely skinning the otter by pulling back on the fur and carefully cutting away the flesh. The pelt, which provides little information about cause of death, was unceremoniously dropped into the trash.
The furless otter looked gruesome, like a red and maroon E. T. with big teeth and a long rib cage, but I was the only one focused on the entire animal. The rest of the humans in the room were swarming around the table and digging into the carcass to collect very specific tissue samples for measurement and later study—testes, lymph nodes, thyroid, adrenal gland, even the tonsils, which can provide evidence of bacteria entering the body in its diet. Kirkham quickly decapitated the otter and worked for twenty minutes to remove the flesh from its head so she could cut open its skull to examine the brain and collect samples of the cerebrum and cerebellum. At the same time, Worman removed and weighed the major organs, each of which was closely examined for abnormalities. Any apparent blemish on the surface of an organ was sliced open to determine if the blemish extended deep into the tissue, which could be an indication of disease. Throughout the process, they called out numbers for Jorgensen to record on data forms, and when she was too busy, they wrote the numbers in otter blood on the steel table.
Worman then collected a urine sample in a syringe and noted that it appeared red and cloudy, a sign of bladder inflammation. The gallbladder was examined for signs of parasites—only one was found—and a sample of bile was collected to test for toxins from harmful algal blooms. Its liver was found to be unusually small with “sharp margins,” another sign that the otter hadn’t been eating well. There was nothing in the colon or stomach, but the latter had signs of a bleeding ulcer. The lungs, which Worman said should be “pink and fluffy,” had lost their form and appeared rubbery. She looked through yards and yards of intestines and found just one thorny-headed worm, a common parasite, then struggled to collect a sample of heart blood because most of the blood had already clotted. Next she measured the heart valves and followed the path of blood through the heart and lungs, looking for abnormalities. There was no smoking gun in all of these findings, just a litany of minor issues that indicated the otter was unhealthy.
Three and a half hours after beginning, during one of the last steps in the necropsy, Worman found what she believed killed the otter—a pea-size lesion in the aortic valve, where the blood exits the heart. Consisting of numerous colonies of bacteria, the lesion is the diagnostic sign of vegetative valvular endocarditis, which leads to congestive heart failure and a variety of infections. It’s a common cause of death in otters in south-central Alaska.
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VEGETATIVE VALVULAR endocarditis was the official cause of death of sea otter FW14026, but its heart condition was caused by one of several varieties of the streptococcus bacterium. Strep syndrome, as the otter biologists and pathologists call it, is the leading cause of death of sea otters in Alaska. A 10-year study of 144 dead sea otters found that 60 of the animals died as a direct result of strep. But what causes strep syndrome is entirely unknown. Verena Gill, a US Fish and Wildlife Service biologist who studied the health of Alaska’s sea otter population for a dozen years before transferring to the Bureau of Ocean Energy Management in 2014, told me that the general consensus is that strep is probably caused by something stressing an otter’s immune system and making it more susceptible to disease. “At first we thought maybe they were getting it from wounds or from bad teeth,” she said. “But now we’re starting to think it’s normal for sea otters to carry these kind of organisms around, and it grows when their immune system is suppressed. What causes the stress could be anything—it could be another disease, we don’t really know. But they come in and they die from a growth on their heart valve and then they test positive for strep. We have not gotten to the bottom of what’s causing it.”
The heart condition that results from strep syndrome was first discovered in sea otters in Kachemak Bay in Homer in 1998, and by 2006 there were so many dead otters washing up on beaches there that the government declared an “unusual mortality event,” an official designation under the Marine Mammal Protection Act that requires immediate government action in response to a significant and unexpected die-off of a protected species. That’s how Kristin Worman was hired by the Fish and Wildlife Service—first as a summer worker walking the beaches in Homer to collect sea otter carcasses for study and then in her current position conducting otter necropsies.
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ONE OF THE SIGNIFICANT discoveries that came out of the work following the unusual mortality event declaration was an otter survey of Kachemak Bay that found thousands of sea otters in the area, when prior to that experts had believed the population totaled only about nine hundred animals. At first the biologists believed that the large number of dead sea otters was not unusual given that the otter population was much larger than originally thought. And even when so many of them were found to have died from strep syndrome, some biologists like Gill thought that strep was “just what they die of up here.” But now she thinks otherwise. To have such a high proportion of sea otters die from this one disease was anything but natural, she said.
While strep syndrome remains the leading cause of death among otters in Alaska, they die from dozens of other things as well. Trauma, both human-caused and that administered by other animals, is second on the list. Typical mortality from trauma occurs due to boat strikes, gunshot wounds, injuries caused by fighting with other otters, mating trauma, and predation by killer whales. Bald eagles will occasionally capture and consume sea otter pups, as well. Legal hunting of sea otters by Native Alaskans is not included in studies of sea otter mortality, even though hunting may be the leading cause of death some years, with as many as 1,500 animals killed by hunters annually in recent years.
Most commonly, however, numerous factors contribute to the death of an otter. In the case of sea otter FW14026, when the test results came back on the various samples collected during its necropsy, it was found that in addition to strep syndrome it had a bacterium in its brain associated with meningitis. That kind of finding is quite common. Gill said that it is extremely difficult to categorize the cause of death of most sea otters because so many different factors contribute. She recalled two otters that were struck by boats off Kodiak Island, but when they were tested it was found that they were loaded with huge levels of the biotoxin that causes paralytic shellfish poisoning. The boaters reported that the otters had barely moved as the boat approached, which, as it turns out, is a common behavior among otters affected by the toxin. So were the otters killed by the boat strike or by paralytic shellfish poisoning? Many otters that are found to have been killed by predators were ill from any number of diseases. And the predators—usually great white sharks in California and killer whales in the Aleutian Islands—probably sensed they were an easy target. While the predators struck the final blow on those otters, the diseases were probably just as culpable for the death of those animals.
On the other hand, juvenile male sea otters will often die from what Gill says is stupidity. “One just packed his gut so much with mussels that he couldn’t pass anything and died. Or they’ll eat fish discards at the dock, because they’re stupid and haven’t figured out yet that’s a bad idea, and they’ll perforate their guts with fish bone
s. There are a lot of parasites in those fish discards, and the parasites will perforate their guts. One guy last week drowned, but he had eaten a lot of fish discards full of parasites, perforated his gut, and he drowned. But really the cause of death was stupidity.”
Sea otters in Alaska have died from some rather strange things, too. Cancer is unexpectedly common, and otters die as a result of oil spills quite regularly, even in areas where an oil spill has not been reported. Phocine distemper, a virus that killed twenty thousand gray and harbor seals in Europe in 1988 and 2002, had never been recorded in the Pacific Ocean until it was found to be a contributing factor in the death of a number of sea otters in Alaska in the 2000s. Gill theorizes that it arrived via seals crossing the Northwest Passage. There has even been a case of a sea otter dying from histoplasmosis, an infection typically found in the Midwest that is caused by inhaling the spores of a fungus found in bird and bat droppings.
The good news from all of the health studies of sea otters in Alaska, especially the large number of carcasses turning up on the shores of Homer, is that there does not appear to be a disproportionate number of dead and dying otters in any particular age or gender group. “That’s a hopeful sign,” concluded Worman. “Since there isn’t a specific segment of the population that is succumbing, it suggests that the population is generally healthy and thriving.”
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THE STORY OF sea otter health in California, however, is very different from that in Alaska. Strep syndrome, for instance, is hardly ever encountered in California, and when it is, pathologists look at it as a curiosity rather than a dire concern. According to Melissa Miller, a veterinary pathologist at the California Marine Wildlife Veterinary Care and Research Center in Santa Cruz, shark bites appear to be the leading cause of death among sea otters in California, but she is more concerned with the effects of disease-causing microorganisms and pollutants, especially those that originate on land. There’s not much that can be done about sharks, but most of the microorganisms that are killing sea otters in California are a direct result of human activities. “There’s no question that sea otters are getting bombarded with pollutants of all different kinds—chemical, biological, biotoxins—and horrific amounts of them,” Miller said. And it is not uncommon for her to find evidence of several different parasites, pollutants, or toxins in just one animal. In fact, she told me, that’s pretty much the rule. “And the tricky part,” she said, “is figuring out which was the first domino to fall or how did all of those things result in the dead animal that’s on my table.”
Strangely enough, Miller’s greatest worry of late is cat feces. A protozoan parasite called Toxoplasma gondii actively reproduces in a variety of wild and domestic cat species, and the cells of the parasite’s eggs pass through the cat in its feces, where it is believed to survive in the environment for months or years. Researchers speculate that the parasite then makes its way to coastal waters when cat litter is flushed down the toilet or when heavy rains wash it into storm drains. Male sea otters in California have a 70 percent chance of being infected with it, an amazingly high rate given that the only known hosts are mountain lions, bobcats, and domestic cats. How the parasite gets into sea otters is uncertain, but it is probably absorbed by filter-feeding mollusks or consumed by snails as they graze on seaweed, and those animals are then eaten by otters. It has become such a grave issue that the bill that passed the California legislature in 2006 to establish the California Sea Otter Fund also included provisions requiring that packages of cat litter sold in the state be labeled with proper disposal methods to protect otters.
No one knows when Toxoplasma first began infecting sea otters. Nancy Thomas at the US Geological Survey’s National Wildlife Health Center in Wisconsin was the first pathologist to examine sea otters in any detail back in the early 1990s, and she found it in some of the first animals she tested. Just because a large number of dead otters are infected with Toxoplasma, however, does not mean that it is responsible for killing the animals. Miller says it typically lingers in the background and has an indeterminate effect. But she calls the parasite “a great biological marker for the extent that sea otters get exposed to land-based pollution.” That’s her take-home message—abundant quantities of terrestrial pollutants are finding their way into the nearshore environment and sickening marine wildlife—and that message comes with a long list of other land-based pollutants that are also being found in dead sea otters, some of which are rather unusual.
For instance, dead sea otters are turning up with a brain disease typically found in horses, equine protozoal myeloencephalitis, which is caused by a single-celled parasite called Sarcocystis neurona that is very similar to the one that causes Toxoplasma. But Sarcocystis comes from the feces of opossums, which aren’t even native to California. Miller said the two diseases are very similar. The only difference is one comes from cat feces and the other from opossum feces. Sarcocystis, which killed forty otters in Morro Bay in April 2004 following a large rainstorm that probably washed the parasite into the bay, tends to kill otters that feed primarily on clams and innkeeper worms, while Toxoplasma kills mostly snail-eating otters. But beyond that, little is known about either parasite’s transmission.
In addition, Miller has found roundworms in sea otter brains that are almost certainly the same parasite found in raccoons, and she even discovered one case of an otter infected with a parasite that likely originated in a rat. And in 2007, she started seeing dead otters that appeared to be bright yellow in color; she eventually traced this to a freshwater toxin called microcystin that is commonly found in farm ponds. She later discovered that microcystin was being washed into the Pajaro River in Watsonville and flowing thirteen miles downstream to Monterey Bay. The first recorded case of an otter dying from the toxin occurred right at the mouth of the river.
The link between the land and sea is the most critical component of these sea otter deaths. Harbors, bays, and other locations where freshwater enters the marine environment accumulate a wide range of other nasty stuff, too, including effluent from wastewater treatment facilities, pesticides, industrial chemicals, and organic pollutants like PCBs, all of which have been found in sea otters. These areas tend to be high-risk sites for otter mortality. This land-sea link makes sea otters sentinels not only for the health of the coastal marine environment where they live, but also for the health of the terrestrial environment. And because these are all terrestrial pathogens and man-made pollutants, sea otters have little natural immunity to them.
Land-based pathogens aren’t the only reasons that southern sea otters are getting sick, though. They’re facing numerous marine factors as well, just like in Alaska, including domoic acid and paralytic shellfish poisoning, both of which are associated with algal blooms. Domoic acid, a neurotoxin, was first discovered to be a problem in 1998, when it caused a large number of sea lion deaths in California. It causes seizures in the animals, and they are often observed to vomit and behave like they are constantly itching. Humans who survive eating shellfish contaminated with domoic acid often experience memory loss. It is believed that the toxins from an algal bloom will get into fish first, followed by the sea lions that eat the infected fish. It takes a while before the toxin reaches the animals on the seafloor and those like sea otters who eat the benthic creatures. “I typically can set my watch and say, we’ve got sea lions coming in with domoic acid, so maybe a month from now we’ll start seeing otters” with it, Miller said.
The one cause of death that just makes my head spin is mating trauma. Mating among sea otters is no romantic affair. It’s a violent act that typically involves the male biting the female’s nose. Just about every female otter of reproductive age has scars on her nose from this vicious behavior, and some have even had their nose ripped entirely off. The behavior is much more common among otters in California than in Alaska, so much so that otter biologist Jack Ames has joked that Alaska otters should be brought to California to introduce “gentleman genes” to t
he California population. While it’s not unusual among Mustelid males to bite the neck or the nose during mating, southern sea otters tend to go a little overboard in their aggression. Unfortunately, open wounds on the nose are a portal of entry for bacteria and other organisms that cause infections that can often lead to death, especially when the injured otter may also be fighting off Toxoplasma or Sarcocystis or any of the other disease-causing microorganisms. Sometimes the injured nose will swell up, making it difficult for the animal to breathe and leading to problems in its lungs. There have even been documented cases where a male sea otter has actually drowned a female while mating.
According to Miller, it’s not just female sea otters that are injured from aggressive males, however. Competition for females often leads male otters to bite other males. She said it is not uncommon to find scarring on the noses, paws, flippers, and testicles of male otters that almost certainly was caused by other males. And occasionally she has even found males whose baculum, or penis bone, was broken from a bite. “If you think about it, it’s a pretty good strategy if you want to get Bob out of commission,” she said. There are also records of male sea otters that have raped and killed harbor seal pups, which sounds almost like a made-up story in a tabloid newspaper but which Miller said “would not be classified as abnormal in the animal sense.” (It still sounds pretty disturbing to me.) She pointed to Elkhorn Slough, an estuary off Monterey Bay where sea otters live amid a harbor seal rookery, as a site where such behavior probably takes place, where male otters with raging hormones are in close proximity to young seals that don’t fight back.