MOLT IN THE NORTHERN FUR SEAL 



by 



Victor B. Scheffer and Ancel M. Johnson 



Wildlife Biologists 



Bureau of Commercial Fisheries 



Marine Mammal Biological Laboratory 



U. S. Fish and Wildlife Service 



Seattle, Washington 



ABSTRACT 



Growth and replacement of the fibers of the back pelage were studied on 706 fur 

 seals (Callorhinus ursinus), of which 321 were in molt. Duration of molt in the indi- 

 vidual is about 15 weeks. Extreme duration of the molting season is mid-June to mid- 

 March of the following year. The estimated mid-dates of molt for 1-year males and 

 females are, respectively, 11 September and 26 September; for 10-year males and 

 females, 12 October and 13 November. The mid-date for males is 3.4 days later with 

 each year of age; for females 5.5days. Fur fibers tend to accumulate in the skin with 

 age. Thefurfiber count per bundle rises from 14 to 24 (mean 17.9) in the first pelage 

 to 51 in the adult female and 68 in the adult male. In 120 seals of various ages and 

 both sexes, the mean count of fur fibers per bundle is 39.2. The black birth coat is 

 replaced by the silvery adult-type pelage at about age 3 months. The skin thickens 

 with age and with molt. Sebaceous glands are functional at birth; sweat glands and 

 their surrounding fat cells do not mature until the end of the first year. 



Pilosebaceous units (each with a guard hair, a fur bundle, a skin pore, and as- 

 sociated structures) disperse as the seal increases in age and body surface area. The 

 number of units per cm.'^ is 1,296 for a 3-year male and 790 for a 15-year female. 

 The unit count on the back is similar to the count on the belly, and the number of fur 

 fibers per bundle is similar on back and belly. In the back pelage of the 12-year 

 female there are estimated to be 275,634 total fibers per inch 2. 



INTRODUCTION 



season. Notes on corollary changes in the skin 



General information on the pelage of the are included. The main purpose of the study is 



northern fur seal, Callorhinus ursinus, with a to provide information on molt so that pelts 



glossary of technical terms, was recently can be harvested by the Government at the 



published (Scheffer, 1962). Now specific evi- time when molt is not in progress, that is, 



dence is offered on growth and replacement of when the pelts are of greatest commercial 



the pelage fibers with relation to age, sex, and value. 



