April 6, 2011

Six Flags Discovery Kingdom Announces
Rare Pregnancy of Pacific Walrus

One of the world’s most familiar animals is also one of the rarest of any found in a zoological park or oceanarium facility. Rarer still is the possibility of a birth, yet
Six Flags Discovery Kingdom is awaiting its first Pacific walrus calf in a matter of weeks. Among the 17 walruses currently living in U.S. facilities, the park’s three individuals are also among the few that are still viable breeders.

“There have been no more than 11 recorded walrus calves born in North American zoological facilities since 1931,” said Michael Muraco, Six Flags
Discovery Kingdom’s Animal Care Director. “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 are cautiously optimistic about the odds of survival—about
50 percent—and because the pregnancy alone has represented so many unchartered milestones, they already acknowledge tremendous success. The park’s walrus population is comprised of three 16-year-old individuals – the male Sivuqaq and two females, Uquq and Siku. Over the years, as the group matured, it was thought that breeding would occur naturally, but “timing” was always an issue with the females’ breeding season not matching the male’s seasonal rut.

The work of outside marine mammal reproductive physiologist Holley Muraco has been instrumental in the current state of affairs, and in many ways, has produced many “firsts.” One such achievement was solving the mystery of why walruses rarely reproduce in captivity.  Muraco was able to pinpoint sunlight as the primary regulator of the male reproductive season— photoperiod—where sunlight alters the timing. This pregnancy is also the first time that captive walruses have been reproductively assisted with success and the first moment of conception and implantation have been monitored and documented. In working with the male Sivuqaq, Ms. Muraco has tracked the production of walrus sperm and even captured walrus mating on video.

“The pregnancy was confirmed via ultrasound in the Fall—even though we were fairly confident of the situation through our tracking of the significant changes in hormone levels and other physiological changes,” said Ms. Muraco.

Courtship behaviors have also been studied and documented.  Ms. Muraco observed the male walrus, Sivuqaq, inflating his throat sac to the point where it had enlarged to twice the size of his head, a behavior that has not been widely reported and never documented in a zoological facility.  The unusual courtship display by Uquq was documented on video and recent courtship by the other female, Siku, during her estrus period, was also closely observed.

“Pacific walruses remain one of the least studied and most mysterious pinniped species with a complex reproductive biology adapted to life in the Arctic,” said
Ms. Muraco. “Although they live long healthy lives in zoos and aquariums, they don’t reproduce very often. 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.”

Additionally, Ms. Muraco has studied the walrus biomarkers at the park, including salivary testing to monitor estradiol and progesterone in the females and testosterone in the males. At one point, she discovered that Uquq’s progesterone level was twice as high as it ever was during a certain phase of her reproductive cycle, then a few months later, 10 times as high. This was a clear indication that, in addition to dramatically different physiological changes, Uquq was most likely pregnant. And while gestation in a walrus is believed to be 18 months, this timeline has never been proven. By documenting the progress of Uquq’s pregnancy, from conception to eventual birth, it will represent the first time ever the gestational period is verified.

“Alaska Natives state that they know a walrus is pregnant only in the late winter/early spring because they are fatter than the non-pregnant females,” said Mr. Muraco. “That is the only time period—very late pregnancy—that outward appearance gives any indicators of pregnancy. And while the norm was that visualization of a fetus via ultrasound would not be possible until a month or so before birth, Holley was able to find a live, moving fetus as early as five months ago.”

The park acquired the orphaned walrus calves in 1994, recovered from a federally authorized Native Alaskan subsistence hunt near Gambell, Alaska on St. Lawrence Island in the Bering Sea. At the time, the park was one of only a few zoological institutions in the country authorized by the U.S. Fish and Wildlife Service to take in and care for beached and stranded Pacific walrus calves.