Return of the Sea Otter

by Todd McLeish

But what she did have were innate senses that required no training to develop. According to Strobel, the little that is known about otter senses primarily involves their vision. She said sea otter vision is a mixed bag. Based on their eye anatomy, they appear to see equally well in the air and in the water, and they are adapted for life in a shallow-water environment where they must function in both the bright light above the water and the reduced light below. Unlike the deep-diving marine mammals like elephant seals, which are well adapted to very dark conditions, sea otters do not see well in the dark. Strobel said that an eye adapted for seeing in the air is usually not going to see well underwater, and vice versa. “Humans are a great example of that,” she said.

  Sea otters have a flat or lenticular lens common to terrestrial mammals, enabling them to see well in the air, whereas most marine mammals have a spherical lens more adapted to life in the marine environment. But when otters dive beneath the surface, they are able to—with what scientists call an accommodative mechanism—force their lenses to bulge outward to create the spherical shape that allows them to see better underwater. “We don’t really know how it works,” Strobel said, “but we assume a muscle can change where the fluid is and create differences in pressure.”

  As for their hearing, it’s not particularly good when compared to other marine mammals, although it’s still better than humans’ hearing. But sea otters don’t seem to need excellent hearing. Their prey is all rather silent, and the ocean is quite noisy, so they do not appear to have developed any special adaptations to hear especially well. While humans can hear in the range of 20 hertz to 20 kilohertz, sea otters have a slightly wider hearing range in the air—5 hertz to 32 kilohertz—while underwater they lose much of the lower frequencies and can hear sounds only above 250 hertz. However, their hearing seems to be particularly tuned to the frequency range between 8 and 16 kilohertz, which may be the frequency of the calls of sea otter pups. Communication between mother and pup is believed to be the primary sound that they need to detect. Because mothers and pups regularly get separated, they vocalize to find each other—the pup repeatedly squeals to call for its mother, and the mother responds with a slightly lower sound until they are reunited. Whether they use their hearing in any significant way outside of this social context is uncertain.

  Tim Tinker isn’t convinced that sea otters don’t have extraordinary hearing, though. He said they seem particularly skilled at detecting and interpreting the danger inherent in the sounds of the boat and equipment he uses to capture sea otters for his research. “They’re pretty amazing at hearing us,” he said. “Maybe it’s more about detecting a particular signal. They seem to know the sound of our dive equipment being put into the water. But for everything else, their hearing isn’t so great.”

  Almost nothing is known about the sea otter’s sense of smell, although as Mustelids otters come from a history of animals that use scent in territory marking and mate finding. Like many mammals, they are known to smell each other when they first meet, especially around the nether regions. But no studies have yet been conducted to reveal more about their olfactory capabilities.

  The same is true of their sense of taste, although they appear to have very strong food preferences in captivity. They love shrimp and they avoid squid, for instance, so it is clear that they can tell the difference between the two. But they also may be able to detect some degree of toxicity in clams and other invertebrate prey. One study suggests that sea otters can taste a little bit of a clam and determine whether it is infected with the toxic algae that causes paralytic shellfish poisoning, something that humans are unable to do. The researchers fed clams containing various levels of the toxin to captive sea otters, and they found the animals could detect the toxin and avoided the clams with the highest levels. Of the clams containing low levels of the toxin, the otters ate only the nontoxic parts, especially avoiding the highly toxic siphons. Juvenile otters were unable to make this distinction.

  Tinker has observed a similar behavior in the wild sea otters he has studied. He said that otters prefer to eat sea urchins when they are gravid with eggs, and after tasting them they sometimes discard those that have already spawned. “I’ve seen them bring up an urchin, take one bite, and throw it away,” he said. “They do that in March right after the urchins spawn. It’s like a taste test. You see them taste it and then decide whether to discard it or accept it.”

  Perhaps sea otters’ most important sense is their tactile abilities, defined primarily by the use of their forepaws and whiskers. Strobel described “the stereotypical sea otter behavior” as feeling around for everything they can get their hands on and manipulating it to learn about it. “They’re always feeling new things, even if they’re not even looking at it,” she said. And their use of tools is another indication of the importance of their sense of touch. “They’re very extractive predators. They pick prey that they are forced to handle and extract something [from]. Just from observations, it seems like an incredibly strong and important sense for them.” A 1968 study of the brains of various otter species found that the portion of the brain dedicated to tactile stimuli is enlarged compared to that of other Mustelid species.

  Less is known about the use of their whiskers, which relay tactile information to their brains. Although sea otters are more closely related to terrestrial otters, their whiskers are more similar to those of seals and sea lions. Sea otters have about 120 whiskers, which is about the same as most seals, and the internal anatomy of their whiskers is also more like that of seals and sea lions than other species of otters. Whisker hair follicles are made up of collagen capsules containing flexible tissues, blood-filled sinuses, and nerves. When whisker hairs move, they send information to the brain via axons in vibrissal nerves. The sensitivity of each hair follicle is determined by the number of axons in the vibrissal nerves. Like seals and sea lions, sea otters have about 1,340 axons, nearly three times as many as river otters do, suggesting that the whiskers are highly sensitive.

  Tinker believes that sea otters use their whiskers in some way for foraging, though he isn’t sure exactly how. He told me that some of the otters he has captured in soft sediment areas of Alaska, like Zachar Bay and Clam Lagoon in the Aleutians, have whiskers that are worn down to stubble on one side of their face. “That’s something we’d never seen anywhere else,” he said. “You travel two kilometers away to the outer coast where they’re eating urchins, and they all had normal-size whiskers. That tells us that they’re using their whiskers for something in that soft-sediment area. We don’t know what, though, because we’ve never been under the water with them.” He speculated that the stubble is a by-product of their sliding one side of their face against abrasive material as they search and dig for clams. But why just one side? “I’ve seen pictures of them swimming along with one side of their face down,” he said. “They could be detecting something on the bottom that way. They could be looking for a siphon hole from a clam or detecting the flow of water coming from a siphon. Those are clues that maybe a whisker could help them with.”

  But, he admits, no one really knows.

  Chapter 5: Surrogate Mothers

  CANNERY ROW, MONTEREY, CALIFORNIA

  IN THE OFFICE of the Sea Otter Research and Conservation program on the roof of the Monterey Bay Aquarium, Karl Mayer stared at a computer screen showing images of four of the six tanks where rehabilitating sea otters could be observed remotely. One circular tank contained four male otters, two of which were destined for release back into the wild within days and two of which would remain permanently in captivity at a research facility in Santa Cruz. Another tank contained a five-week-old female, while an eleven-day-old female received round-the-clock care in a third tank designated the intensive care unit. In the fourth tank, an adult female named Gidget, a permanent resident of the aquarium, cuddled on a platform in the middle of the tank with a young male who, just two days earlier, was introduced to Gidget as her surrogate pup. All of the young otters h
ad been rescued after being found stranded on beaches on the central California coast.

  As we watched, Mayer donned a black cape and dark welder’s mask—an outfit the otter rehabilitators call the “Darth Vader look”—to bottle-feed the youngest of his charges, dubbed Otter 679. One of the most important strategies in raising a sea otter pup for release is to ensure it does not become imprinted on humans, hence the Darth Vader getup, which disguises Mayer so the otter doesn’t know it is being cared for by a human. The feeding lasted just a couple minutes before Mayer placed the fluffy pup in the water to defecate, then dried her off and placed her on a platform beside the water. Mayer said this pup, discovered at Jalama Beach, which is near the southern end of the California sea otter’s range, was probably born premature, and despite being nearly two weeks old, she was acting more like a one- or two-day-old otter. “She’s circling the drain,” he said, suggesting that her survival was far from certain. Every four hours an aquarium staff member or volunteer fed and groomed her, placed her in the water for thirty to forty minutes to acclimate her to her future environment, and then allowed her to nap.

  Mayer returned to the office momentarily to make some notes before quickly turning around to visit the other young female otter, which was being introduced to solid food for the first time. Captive sea otter pups are fed only formula until they are about four weeks old. For the next four weeks they get a combination of formula and solid food, before being weaned from the formula at eight weeks of age. Pups begin to shed their fluffy natal pelage when they are a month old—a process that lasts four or five weeks—after which they no longer float like a cork and can begin to learn to dive beneath the surface of the water.

  Mayer described his job as “a nonstop care scenario” in which he is continually assessing which otter needs what and when, and directing a team of four staff members and sixty-five students and volunteers to administer whatever care is necessary. Throughout our conversation, we were frequently interrupted by volunteers with questions and minor emergencies that Mayer had to address. He is in charge of everything at the aquarium that has to do with stranded sea otters, from responding to calls about injured otters and caring for them for sometimes months at a time, to determining animal-care protocols, training and supervising staff and volunteers, and coordinating the release of the animals and their postrelease tracking. It isn’t at all what he initially envisioned for a career. Mayer thought he was going to become an attorney. But after volunteering at a marine-mammal rehabilitation center and spending a semester studying marine science at Woods Hole Oceanographic Institution, he decided to pursue a career in fisheries. After a stint as a fisheries observer for the National Marine Fisheries Service, he landed a part-time position in 1993 at the Monterey Bay Aquarium rehabilitating sea otters. He turned what he thought was going to be a brief stop into a lifelong career, and as the aquarium’s otter activities grew and evolved, his role grew right along with them.

  It’s a rare day that the sea otter rehabilitation team at the aquarium does not get a phone call about a stranded sea otter. The six tanks available for rehabilitating otters at the aquarium are almost always occupied. One of Mayer’s greatest struggles is creating space to accommodate additional stranded otter pups. But because there are few other licensed otter-rehabilitation facilities in California, the aquarium is the first responder.

  The Marine Mammal Stranding Network in California, a group of non-profit organizations, biologists, and volunteers who respond to animals found stranded or injured on local beaches, has been in operation since 1975. Managed primarily by the National Marine Fisheries Service, it responds to six to eight hundred calls each year about stranded seals, sea lions, dolphins, sea otters, and other animals along the six hundred miles of the state’s central and northern coastline. When environmental officials, beach or park attendants, or anyone else observes a stranded marine mammal, they call the center, and if the animal is a sea otter, that call is directed to Mayer’s office.

  Few stranded adult sea otters are captured and treated unless their injury is human caused, like a boat strike, fishing gear entanglement, or gunshot. In most cases, stranded adults are typically too far gone by the time they make it up on a beach and are discovered. Due to their high metabolism, if they haven’t eaten in a day or more, their system begins to shut down. Stranded adults are usually diseased or geriatric and untreatable, and euthanasia is often the most humane option. That is especially true if the animal is an adult male, which biologists say have little value to the overall population. Rehabilitating and releasing adult males in an area that is already at carrying capacity could do more harm than good by displacing other wild sea otters. “We really can’t justify rehabilitating adult males,” Mayer said. “Adult females are really the most important component of the population because they’re the reproducers.”

  That’s not to say, however, that stranded adult male sea otters—or any others—will be left on the beach to fend for themselves. If there are people and dogs around and the otter is not exhibiting a flight response, the stranding team will intercede to protect it. Mayer said that those are often immature animals, in what he calls “the young and dumb category,” that don’t know they should avoid people and other large animals. In that case, the team may simply capture and relocate the otter.

  If it’s a pup, the approach is entirely different. The first step in assessing a stranded otter pup is to see if it can be reunited with its mother in the wild. Sometimes the two are separated inadvertently and just can’t find each other. In about 10 percent of pup-stranding cases, the response team is successful at reuniting mothers and pups. If that doesn’t work, or if the pup appears unhealthy or malnourished, it is captured and brought to the aquarium.

  Regardless of the animal’s age, once it arrives at the aquarium, it is thoroughly examined by veterinarian Mike Murray to identify any physiological reasons for why it stranded and to determine how to address any medical issues. Then comes the surprisingly challenging process of feeding the otter. “Here’s an animal that has probably been struggling to eat and is obviously going to be hungry, so it should be a slam dunk to get it to eat, but it doesn’t really work that way,” Mayer said. That is often the case with recently weaned pups that have stranded due to an intestinal parasite they get from eating sand crabs. If the otter finds itself in sandy habitat, sand crabs can be abundant and easy for it to catch and consume. But the crab parasite eventually perforates the otter’s intestinal wall, causing considerable pain and an unwillingness to eat.

  Young pups require round-the-clock care during their first weeks at the aquarium, but by the eighth week they are ready to be introduced to a surrogate mother who will teach them how to feed themselves and survive in the wild. But that’s a relatively recent development in the otter-rehabilitation program.

  * * *

  THE MONTEREY BAY AQUARIUM opened to the public in 1984, and sea otters played an important role from the very beginning, in part because of the facility’s location in the center of the otters’ California range. The aquarium’s very first veterinarian, Tom Williams, had a personal interest in the species and even raised some sea otter pups in his bathtub at home before the rehabilitation program got under way. He conducted some basic research on sea otters in those early days, and when the aquarium began receiving calls about stranded otters—some even before it opened—an exhibit originally designed to house seabirds was converted for sea otters. It has been one of the aquarium’s most popular exhibits ever since.

  Little was known about how best to care for captive sea otters when the exhibit first opened, and even less was known about how to rear them so they could be released back into the wild. Stranded pups were initially raised by a group of volunteers who treated them as if they were their own children. Karl Mayer described it as a hands-on, intensive, round-the-clock process during which the pups bonded with their caregivers so much that the animals couldn’t be left alone. Early attempts to relea
se them back into the wild were met with little success. The first male on permanent exhibit, Roscoe, was a recaptured animal. Little effort was made to monitor released otters back then, so little is known about how well they fared, though some—like Roscoe—were so habituated to people that they created problems by climbing on marina docks and interacting with scuba divers, kayakers, and fishermen.

  There were also concerns that the captive-reared pups weren’t learning how to survive on their own in the wild, so an ocean-swimming program was developed to introduce them to the marine environment and how to find food. Every day Mayer and his colleagues donned wet suits and took the pups into the bay just beyond the aquarium, taking advantage of the fact that the otters had bonded with humans and would not swim away. Every time Mayer would dive to the seafloor to look for otter prey, the pups followed alongside and learned how to do it themselves. Eventually Mayer found himself swimming with sea otter pups for several hours every day, a job that sounds to me like the ideal occupation.

  “I learned an incredible amount about sea otters and sea otter behavior from going through that process,” Mayer said. “Obviously it’s a pretty intimate sea otter–eye view of their life, learning what it takes to hold your breath and go down to the bottom and find prey items and bring them back up and crack them. The pups are really tethered to you. The first couple times you go out there you’re scared you’re going to lose them, and then you quickly realize there’s no way you’re going to lose them. They’re glued to you.”

  While the swimming program appeared to help the otters survive in the wild, they were still bonded to their human caregivers. And as the aquarium began to ramp up its efforts to monitor the otters after release, they repeatedly found that they had to intercede in human-otter conflicts by recapturing the animals and relocating them elsewhere. So in 1999 Mayer decided to use a disguise during the hand-rearing process while also continuing to swim with them in the ocean. It wasn’t enough. The otter pups continued to create conflicts with people once they were released.