Orphaned Otters Find a Home
At California's Monterey Bay Aquarium, researchers are preparing rescued sea otters to return to their native kelp forests in the Pacific Ocean.
Otter 540 washed up on California's central coast in April 2011, a day-old, sand-covered furball weighing just over two pounds. Otter 545 was found three weeks later. At about four and a half pounds, it was significantly more mature than 540, having benefited from additional time spent with its mother. The otters, both of them discovered by beachgoers, were eventually taken to the Monterey Bay Aquarium, to be cared for by its Sea Otter Research and Conservation program (SORAC). While one orphan showed promise of returning to the wild, the other seemed destined for an aquarium exhibit.
Despite their dramatically different fates, both pups represent the challenges facing their species. With about 2,700 individuals living along the California coast, southern sea otters are listed as threatened under the Endangered Species Act. Through a multifaceted approach that includes otter research, rescue, and rehabilitation as well as public education through exhibits, SORAC is helping to bolster the population and raise awareness about the otters' important role in their Pacific Ocean ecosystem. "SORAC makes it possible for each rescued stranded animal to go into one of these research streams, as well as rehabilitation and recovery," says Karl Mayer, the program's animal care coordinator. A crucial component of SORAC's success is a surrogate mother program, which pairs orphaned pups with adult female otters, with the goal of ultimately releasing them back into the wild.
SORAC has been studying otters since 1984. When it first started its rehabilitation program, human staffers raised each individual. Those otters became so acclimated to humans, however, that after they were released, they approached people freely, venturing onto beaches and even climbing onto kayaks. As adorable as they look, sea otters have sharp teeth and may bite humans who come too close. The rehabbed otters that had been released had to be recaptured and kept in captivity as exhibit otters.
In 2001, SORAC started its surrogate mother program when researchers paired an orphaned otter with a mother that had lost its own pup. The two bonded. After that initial success, the aquarium began matching rescued pups with female otters that hadn't recently given birth. In most cases, they willingly adopted the orphans.
In the wild, premature separation from their mothers is a death sentence for young otters--they're dependent on their mothers for roughly six months. Rescued pups transitioning through SORAC need about 20 weeks with their adoptive parents to prepare for life in the ocean. "When they are raised by surrogate mothers, their development is more normal," says Mayer. "They retain their wildness. Their survival rate is equal to wild-raised pups."
The program currently has two female surrogates. In addition to 22 rescued orphans that have been returned to the wild, four released female pups have reached adulthood and have produced 15 pups of their own. "The criterion for success is that they must be reproductively contributing to the population," says Mayer.
California's southern sea otters need all the wild members they can get. Though scientists aren't sure why their populations are low, infectious diseases, including sarcocystis and toxoplasmosis, may play a role. Shark attacks on otters have also risen in recent years as more and more elephant seals--typical shark prey--are migrating to California's central coast, with their predators in pursuit.
As otter populations decline, the kelp forests where they live also suffer. Otters are a keystone species, eating sea urchins that, in turn, feed on kelp forests that provide habitat for many other species. "It's top-down control," says Tim Tinker, a research wildlife biologist with the Western Ecological Research Center of the U.S. Geological Survey. Without otters, the sea urchins proliferate and devastate the kelp, causing barren areas where few organisms can thrive.
This past April Otter 545 was released into Elkhorn Slough, a local estuary and saltmarsh with plenty of food to support its resident otters. Sporting purple and blue tags attached to its rear flipper and a radio transmitter implanted in its abdomen, it could be tracked and observed to gauge its progress.
Otters have a high metabolism, and they must eat the equivalent of about 25 percent of their body weight every day. In fact, going even three or four days without enough food can lead them to starvation. If a released otter isn't eating enough, the SORAC team recaptures it and returns it to its tank for an additional week or two before it's again released. "The transition from captivity to [the] wild is so difficult," Mayer says. "They have no experience foraging, finding food, avoiding predators [in the ocean]. It's a release to an unfamiliar environment."
Although Otter 545 swam around during the six days it spent in the slough, it wasn't catching nutritious crabs or abalone. Mayer decided to recapture it and give it more time in SORAC's tank. In May researchers released it a second time, but it again had to be recaptured. This time it had been exposed to an algae toxin and parasites. Mayer treated it and scheduled a third release for this summer.*
Only 30 percent of otters succeed on the first release. The good news is that even individuals like 545 that struggle to adapt apparently learn from their experiences. Nearly all succeed by the third release.