THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 39 



sea otter in its first adult pelage had fewer fur fibers (43) per 

 bundle than two adults (adult male 71 and adult female 91). That 

 the fiber population is denser in the sea otter than in the fur seal 

 (adult female 51, adult male 68) is not surprising. Insulation in 

 the fur seal is provided by both blubber and fur but the sea otter, 

 having no blubber, must depend for insulation only on its fur. It 

 seems reasonable to conclude that fur fibers are retained in the 

 sea otter as they are in the fur seal, thus ''masking" the period 

 of molt. 



John Vania, Leader, Marine Mammal Studies, Alaska Depart- 

 ment of Fish and Game, visited the Marine Mammal Biological 

 Laboratory in Seattle from 8 to 19 November 1966 to work with 

 V. B. Scheffer on the examination of skin samples from sea otters. 

 Of 26 sea otters taken in winter and 20 taken in summer, all 

 showed evidence of molt in some of the fiber roots. This evidence 

 is puzzling; the molt deserves further study. A tentative con- 

 clusion is that, throughout the year, at various places on the body, 

 individual fibers are in molt while others are at rest. 



Observations of captive sea otters also suggested that the period 

 during which fur is shed is prolonged. In all seasons fur fibers 

 were seen on the paws of otters during grooming activity and 

 quantities of fur accumulated at the drain of their pool. 



To estimate the periods of maximum and minimum molt, Cecil 

 Brosseau, Director, the Tacoma Aquarium, collected samples of 

 fur for me from a screen over the drain of a pool that held an 

 adult male sea otter (Gus). The uniformly collected samples con- 

 sisted of the accumulation of fur and guard hair for a 15-hour 

 period at 7-day intervals from October 1967 through October 1968. 

 The samples were dried, cleaned manually (fish scales, fragments 

 of bone, and other debris were removed), and weighed on a beam 

 balance to the nearest 0.01 g. The mean weights of the samples 

 for each month show that shedding is maximal in late spring and 

 summer (mean of 4 August samples = 59 eg.) and minimal in 

 midwinter (mean of 4 January samples = 25 eg.) and that ap- 

 preciable shedding occurs in all months (fig. 20). 



This study suggests that the sea otter exhibits one period of 

 maximal follicular activity (molt) annually in the spring and 

 that it may be similar to the European otter (Lutra lutra) which 

 is said to molt almost imperceptibly during a prolonged period 

 (Novikov, 1956), as does the polecat (McCann, 1955). 



