Six Flags Awaits Rare Birth of Pacific Walrus

Ultrasound of calf expected at Six Flags Vallejo

Times-Herald Online: Six Flags Discovery Kingdom expects within weeks the birth of its first Pacific walrus calf. It's the first time an assisted pregnancy has been successful in captive walruses, a park spokeswoman said. And that's just two of the firsts this pregnancy represents, park spokeswoman Nancy Chan said.

Though one of the world's most familiar animals, the Pacific walrus is one of the rarest found in zoological parks or oceanariums, and calves born in captivity are rarer still, Chan said.

There are 17 walruses living in U.S. facilities, and the park's three are among the few viable breeders, she said. "There have been no more than 11 recorded walrus calves born in North American zoological facilities since 1931," Discovery Kingdom's Animal Care Director Michael Muraco said.

"In fact, so little is known about reproduction in walruses, that in the past two years we have made great strides in understanding more about both reproductive anatomy and breeding strategies between males and females than has ever been recorded. It's been a huge breakthrough and now we have a walrus ready to give birth."

Park officials say they are "cautiously optimistic" about the calf's odds of survival, which is about 50 percent. They say, though, that the pregnancy alone was a "tremendous success," representing as it does many "uncharted" informational "milestones."

The park's walrus population includes three 16-year-olds -- the male Sivuqaq and two females, Uquq and Siku -- which were acquired as orphaned calves in 1994 from a federally authorized Native Alaskan subsistence hunt in the Bering Sea.

Over the years, officials thought breeding would occur naturally, but the "timing" was always off, Chan said. Outside marine mammal reproductive physiologist and Michael Muraco's wife, Holly Muraco, solved the mystery of why, by discovering sunlight is the primary regulator of the male walrus reproductive season. This helps explains why walruses rarely reproduce in captivity, Chan said.

This walrus pregnancy is also the first during which implantation and conception were monitored and documented, Chan said. The pregnancy was confirmed via an ultrasound in the fall, said Holly Muraco.

She studied and documented walrus courtship behaviors, observing the male walrus, Sivuqaq, inflating his throat sac until it was twice the size of his head, Chan said. This is a behavior that has not been widely reported and never documented in a zoological facility, Muraco said.

"Pacific walruses remain one of the least studied and most mysterious pinniped species with a complex reproductive biology adapted to life in the Arctic," she said in a prepared statement.

"Although they live long, healthy lives in zoos and aquariums, they don't reproduce very often," she said. "My studies have focused on understanding why, so that we can maximize reproductive success and answer key questions about their reproductive biology. Hopefully this information will be useful for zoos and aquariums, and also to assist wild animal management."

Also, by documenting Uquq's pregnancy's progress, the gestational period, which is believed to be 18 months, will be verified for the first time, Chan said.