Released Monterey Bay Aquarium Otter Reproduces In The Wild

By Kasia Deuel

Monterey, CA - A stranded sea otter reared as a pup by one of the Monterey Bay Aquarium’s exhibit sea otters and released to the wild two years ago has given birth to a pup of her own – the first for a surrogate-reared animal in the history of the aquarium’s Sea Otter Research and Conservation program (SORAC).

The male pup was born in waters near Moss Landing sometime between July 21 and 28. He appears to be strong and healthy, and to be developing normally, according to Animal Care Coordinator Karl Mayer with the sea otter program. Now almost four months old, the pup is foraging on its own, although he still solicits food from his mother, Mayer said. His surrogate-reared mother seems to be handling first-time motherhood very well, Mayer added.

“She appears to be rearing her pup successfully, and that is very gratifying to all of us at the aquarium,” Mayer said. “The birth is significant because it supports our hypothesis that surrogate-reared pups can survive to adulthood and reproduce successfully.”

The new mother, known to aquarium staff only as “MBA 339,” was found stranded at Manresa State Beach in Santa Cruz County in October 2005 when she was about four weeks old. Initially, she was bottle-fed by SORAC staff and volunteers, who wear black nylon ponchos and a welder’s helmet to hide their human form and eliminate eye contact with pups in their care. The disguise is intended to keep pups from imprinting on humans.

At 6 weeks old – when 339 began to eat solid food – caregivers introduced her to Joy, one of five female sea otters on exhibit at the aquarium. Joy served as her surrogate parent for four months. At weaning age, 339 was implanted with a radio transmitter to allow SORAC staff to keep track of her; on July 5, 2006, she was released to the wild. Sea otter 339 was the second female pup reared by a surrogate mother otter, and the first to give birth in the wild. (The first female surrogate-reared pup is now just over three years old, but has not yet given birth.)

The Monterey Bay Aquarium has been involved in sea otter conservation efforts starting before it opened its doors in 1984. The sea otter research team has made progress in understanding the
conservation and natural history of the southern sea otter, and pioneered many of the medical and surgical procedures used to keep sea otters healthy in zoos and aquariums around the world.

The aquarium’s SORAC team has worked with colleagues for over 20 years on the foraging habits, population dynamics and behavior of hundreds of sea otters. Collectively, results of their studies help provide a picture of an average day in the life of a southern sea otter (Enhydra lutris nereis) – a threatened species in California’s coastal waters. Researchers hope that their work will help explain why the wild population – which over the past three years averaged 2,826 animals – is rebounding so slowly.

A recent disturbing trend in the southern sea otter population is relatively high mortality among reproductive-age adults from infectious diseases. The SORAC team also works with the broader scientific community in a collaborative effort to identify underlying causes of diseases and examine the connections between land-based pollution and disease in otters.

Since 2005, Mayer and SORAC Senior Research Biologist Teri Nicholson have studied surrogate-reared animals in the wild, from release through adulthood, to determine whether these animals survive and, for females, whether they reproduce. The study’s main goal is to determine whether surrogacy is a viable method for rearing and releasing stranded sea otter pups. Preliminary evidence suggests that surrogate-reared pups have a fairly high rate of survival to adulthood in the wild (75 percent have survived to a minimum of 3 years of age) compared to human-reared pups (less than 30 percent). Reproductive success of survivors is still to be determined.

The SORAC program is famous for its efforts to rescue and treat stranded pups and injured adults. Through professional alliances with other aquariums and wildlife rescue facilities in California, the SORAC program responds to every sea otter that strands alive. Until the aquarium began caring for stranded sea otter pups in 1984, virtually nothing was known about how to keep pups alive once they became separated from their mothers.

Over the past two decades, more than 450 sea otters – both adults and pups – have come through the SORAC program, and the aquarium’s staff and veterinarians have developed diets and care protocols that have resulted in a high survival rate for stranded pups and injured or diseased adults.

In recent years, stranded pups rescued by SORAC staff have been introduced to one of three exhibit sea otters – Joy, Toola or Rosa – that rotate duties as surrogate mothers behind the scenes. SORAC staff closely monitor young animals once they’re released, and may recapture those that are not foraging or navigating well. They are brought back to the aquarium to rest and gain weight before being
re-released; sometimes it can take three or four attempts before the young sea otters successfully adapt to life in the wild.

Aquarium staff will continue to track and monitor the progress of the new mother and pup. Currently, there are six surrogate-reared otters in the wild, two males and four females. Of the females, only two are currently of breeding age.