Abstract

The Pacific walrus (Odobenus rosmarus divergens) is a remarkable species that has rarely been studied, and reproduction in particular remains largely unknown. The walrus has been housed in North American zoos and aquariums since the 1930's. However, despite living long lives in zoological facilities, walrus have an extremely low reproductive rate of only 11 births occurring in 80 years in the US. Currently, there are only 11 females and 7 male walrus living in seven US zoos and aquariums. Of these 18 animals, ten are over the age of 23 and the remaining eight animals are between the age of 7 and 17. Long-term population sustainability in these remaining animals is unlikely. Additionally, there has been no reliable influx of stranded walrus placement into public display facilities in the US that could assist with population stability. With continued discussions about listing the Pacific walrus as endangered, time may be running out for maintaining this species in US zoological facilities. At the time of this study, 1.1 nulliparous 16-year-old Pacific walrus were housed at Six Flags Discovery Kingdom, a zoological facility in Northern California. In an attempt to identify the causative reason for the reproductive failure, the animals were monitored in detail for three years using weekly serum endocrinology, daily glans penis smears for sperm morphology, daily vaginal swabs to check for breeding activity and frequent ovarian and testicular ultrasound. Our findings showed that the female consistently ovulated once annually in late December followed by a nine-month pseudopregnancy with sustained elevated progesterone. This non-conceptive estrous cycle profile is consistent with reports from free ranging walrus females.¹ In contrast, the male's seasonal rut consistently occurred from late February–May with a serum testosterone peak in March. This profile differed from the reported annual adult male cycle in free ranging walrus of November–March.¹ During the female's ovulation mid-winter, the male had baseline testosterone and was azoospermic. During the male's spermatogenic rut in the spring, the female had elevated progesterone. The "out-of sync" cycles appeared to be the primary causative reason for the reproductive failure. Since the female was cycling normally, reproductive technology assistance was applied to the male to induce rut at the appropriate time. A treatment protocol was developed based on human studies and will be published in detail at a later date. The treatment successfully induced rut, including elevated testosterone, spermatogenesis, weight gain and reproductive behavior, so that it corresponded to the female's December ovulation. The "sync up" of the cycles resulted in the female's first pregnancy. Using this technology in other individuals with similar profiles, it may be possible to improve the reproductive success of Pacific walrus in US zoos and aquariums. In that regard, the treatment has been replicated in the same male and a second female as well as a male housed with two females at Point Defiance Zoo and Aquarium in Tacoma, Washington.

Acknowledgements

The authors wish to thank Six Flags Discovery Kingdom, Mississippi State University, and Point Defiance Zoo and Aquarium for their support. Individual contribution thanks to Dr. Sam Dover, Dr. Nancy Anderson, Jessa Paschke, Jenifer Cleaner, Toni Rael, Robert Roozendaal, Kelly Smith, Eric Calvo, Dawn Robles, Dr. Peter Ryan, and Dr. Scott Willard.

Reference

1.  Fay FH. 1982. Ecology and biology of the pacific walrus, Odobenus rosmarus divergens Illiger. North American Fauna (74). Washington D.C.: U.S. Department of the Interior, Fish and Wildlife Service.