NOTES 



ANNUAL REPRODUCTION, DEPENDENCY 



PERIOD, AND APPARENT GESTATION PERIOD 



IN TWO CALIFORNIAN SEA OTTERS, 



ENHYDRA LUTRIS 



There are various estimates of the frequency of 

 pupping, dependency period and gestation period 

 for the sea otter, Enhydra lutris. Based upon an 

 evaluation of female urogenital tracts taken at 

 various times of the year and comparing observed 

 population growth rates with theoretical growth 

 rates, Kenyon (1969) and Schneider concluded 

 that female sea otters probably reproduced every 2 

 yr. Sinha et al. (1966) demonstrated that delayed 

 implantation of the blastocyst probably occurred 

 in sea otters. Kenyon (1969) suggested 12-13 mo 

 total gestation period (7-8 mo unimplanted and 

 4.5-5.5 mo implanted) and 11-12 mo for rearing the 

 pup, and a few months rest between weaning and 

 the next estrus. This cycle could be shortened if 

 the female prematurely lost a pup (Schneider 

 footnote 1). Schneider assumed the reproductive 

 cycle included a 7.5 mo gestation period; Bara- 

 bash-Nikiforov (1935) estimated an 8-9 mo gesta- 

 tion period; he later stated that sea otters breed 

 once a year (Barabash-Nikiforov 1969). Lensink 

 (1962) believed that females bred every year, at 

 least when food was not limiting, and recent evi- 

 dence presented by Johnson and Jameson indi- 

 cates annual reproduction in at least some Prince 

 William Sound sea otters. Vandevere (1972) 

 suggested that pup dependency period was less 

 than a year, based on an annual February peak in 

 pupping in California. 



This note describes observations of two tagged 

 female sea otters in California, one seen with a 

 different pup for 6 consecutive yr and the other 

 seen with four different pups in about 5 yr. We 

 also report estimates on the apparent gestation 

 period and pup dependency period for these two 

 sea otters. 



The first sea otter was a female [No. 34; marked 

 with aluminum tags ( Loughlin 1977 )] weighing 22 



'Schneider, K. B. 1972. Reproduction in the female sea ot- 

 ter. Alaska Department of Fish and Game. Sea Otter Rep. I. 36 



P- 



^Schneider, K. B. 1973. Reproduction in the female sea ot- 

 ter. Alaska Department of Fish and Game, Sea Otter Rep. II, 13 



P-, 



Johnson. A. M., and R.Jameson. 1979. Evidence of annual 



reproduction among sea otters. (Abstr.) Third Biennial Con- 

 ference on the Biologj' of Marine Mammals, Oct. 7-11. Seattle, 

 Wash., p. 31. 



kg when captured on 7 March 1976 near Monterey, 

 Calif. It was noted at the time that this female had 

 protruding nipples, a distended abdomen, an en- 

 larged pelvic area, indicating that she may have 

 been pregnant. She was subsequently seen on 13 

 March 1976 with a newborn pup. The female-pup 

 pair was last sighted on 2 April 1976, although the 

 female was sighted often in May 1976 without a 

 pup. The pup was apparently lost after only 2 mo 

 and probably died. On 9 May 1977, female No. 34 

 was seen with a second pup estimated to be 1-3 mo 

 old near San Simeon, Calif (approximately 140 

 km south of Monterey). The last sighting of this 

 pup was on 10 August 1977 at which time it was 

 assumed to be 4-6 mo old. [The pups were not 

 marked, except for No. 34's third pup, and since sea 

 otters are not known to adopt strange pups, we 

 assumed that the pups observed were the same 

 during any 1 yr. Estimates of age for pups were 

 based upon a subjective appraisal of physical ap- 

 pearance and behavior (Lensink 1962; Kenyon 

 1969; Sandegren et al. 1973). The reader is 

 cautioned that our estimates of gestation period 

 are based upon this subjective appraisal.] A third 

 pup, a 3.6 kg female probably not over 1.5 mo old, 

 was captured along with No. 34 on 2 March 1978 

 back near Monterey. This pup was marked with a 

 small tag in one ear and was sighted only once 

 about a week later. It is presumed to have died. 

 Number 34 was observed on 9 January 1979 with a 

 fourth pup. Both were resighted on many occa- 

 sions through 13 September 1979 when this pup 

 was assumed to be slightly over 8 mo of age. This 

 same female was seen with a fifth newborn pup on 

 27 March 1980. This mother-pup pair was seen on 

 at least two subsequent occasions, the last being 8 

 April 1980, but by 5 May 1980 she again was with- 

 out a pup and it presumably died. Number 34 was 

 seen with her sixth pup, judged to be 1 mo old, on 9 

 March 1981 and it was still with the female at the 

 time of writing (Table 1). (Identification of No. 34 is 

 now difficult since she lost her right flipper tag and 

 the left is loose.) 



The second female sea otter (No. 41) weighed 25 

 kg when captured and marked on 15 August 1976 

 near Monterey. She was observed on 8 January 

 1977 with a newborn pup and both were sub- 

 sequently resighted on many occasions. Eight 

 months later, on 8 September 1977, she had a red 

 swollen nose which is indicative of recent copula- 

 tory behavior (Kenyon 1969) and was without her 



FISHERY BULLETIN: VOL. 79, NO. 2, 1981. 



347 



