Abstract

Observation of marine mammal colonies in captivity has made it possible to describe their growth rates, sexual maturation, breeding period, copulative behavior, gestation period, rearing and weaning. These types of behavioral and biological observations are difficult to conduct in the wild. Kamogawa Sea World started keeping walrus in 1983 and has since created a reproductively successful colony that has enjoyed 6 births from 1993 to 2010. The objective of this research is to describe the reproductive and periparturient behavior and calf growth rates experienced at Kamogawa SeaWorld.

An adult male showed annual fluctuation in weight related to the reproductive season. This seems to be the "fatted male phenomenon," seasonal fattening which was observed in California and Seller sea lion.^2,3 During the breeding season, the male made a bell-like sound under water and waited until the female responded by exhibiting signs of estrus behavior.

Copulation or copulative behavior was observed from February 26 to March 22. Copulation was recorded and it continued about 1 minute in the water. Parturition occurred from May 3 to June 5 and average gestation period were 434 ± 7 days (N = 6). It seems the delayed implantation period ended and the fetus start to grow in September (6 months after copulation) from hormonal analysis of urine and body weight change of the mother. The mother gave birth every three years and the mother-calf relationship continued until the next calf was born. Nursing behavior continued two to three years. The adult male was kept with mother and calves, and did not act aggressively towards the others, including the newborn calf.

Body length of six calves (3:3) were 105–110 cm, and average weight at two weeks of age was 64 kg (male 70 kg N = 3, female 58 kg, N = 3). Calves started to eat solid food from 7 months (5–10 months), body weight of calves at that time was 149 kg (Male 168 kg, female 135 kg). Calves suffered iron-deficiency anemia (PCV 15–18%, HGB 6–9 mg/dl, MCV 76–100 fl) at 1–2 years of age. The cause of the deficiency seemed to be the type of food. Our food type for walrus was fish and squid; on the other hand their original food is mollusk mainly that are rich in iron.¹ They recovered from anemia by adding iron, vitamin B complex and folic acid (PCV 45–50%, HGB 17 mg/dl, MCV 120–130 fl). First male calf died 6 years of age; second male calf was moved to another facility when he was 5 years and sired when he was 11 years (stillbirth); third male calf was moved to Hong Kong Ocean Park last year on breeding loan when he was 9 years.

*Presenting author

Literature Cited

1.  Fay FH. 1982. Food and feeding behavior. In: Ecology and Biology of the Pacific Walrus, Odobenus rosmarus divergens. North Am. Fauna 74. Washington D.C. p138–165.

2.  Nitto H, Kawamura T and Baba N. 1998. Changes in body weight of the Steller sea lion (Eumetopias jubatus) in captivity. Jour Jpn Assoc Zool Aqua. 40: 8–13.

3.  Schusterman RJ and Gentry RL. 1970. Development of a fatted male phenomenon in California sea lion. Dev Psychobiol. 4:333–338.