northward to the Farallon Islands, Calif. (Bar- 

 tholomew and Boolootian 1960; Radford et al. 

 1965; Rice et al. 1965; Carlisle and Aplin 1966, 

 1971; Carlisle 1973; Frey and Aplin 1970; Odell 

 1971, 1972, 1974; Le Boeuf et al. 1974; Le Boeuf 

 and Mate 1978; Bonnell et al.'). By 1978 the total 

 population was believed to have increased to an 

 astounding 63,967 animals (Bonnell et al. foot- 

 note 1). 



The northern elephant seal breeding population 

 can be geographically divided into three subpopu- 

 lations by centers of distribution (Figure 1): Baja 

 California; California Channel Islands, including 

 Islas Los Coronados, Baja California; and Central 

 California (Gogan^). 



One can trace a rapid increase in size of the 

 California Channel Island subpopulation 

 (hereinafter called the subpopulation) over the 

 last nearly three decades. Rett (1952) reported 

 seeing a single female on San Miguel Island in 

 1925. Bartholomew and Hubbs (1960) estimated 

 that by 1957 the subpopulation contained 600 

 individuals. Births were first observed on San 

 Miguel Island in 1958 and on San Nicolas Island 

 in 1959, by which time the total subpopulation 

 included an estimated 683 animals (Bartholo- 

 mew and Boolootian 1960). By 1964, there were 

 reportedly 2,158 elephant seals on three islands 

 during the winter breeding season^: San Miguel 

 (1,922), San Nicolas (197), and Santa Barbara (39) 

 (Odell 1971). Based on cumulative data obtained 

 during 4 yr of research, Bonnell et al. (footnote 1) 

 estimated that by 1978 there were approximate- 

 ly 28,316 elephant seals in the subpopulation. 



In this paper we report on counts of northern 

 elephant seals conducted on all the California 

 Channel Islands, including Islas Los Coronados, 

 in February 1972. Using estimated pup production 

 figures from this and other published censuses for 

 the years 1958-78, we then assess rates of growth 

 for each island within the subpopulation and for 



'Bonnell, M. L., B. J. Le Boeuf, M. O. Pierson, D. H. Dettman, 

 G. D. Parrens, C. B. Heath, R. F. Gantt, and D. J. Larsen. 

 1980. Summary of marine mammal and seabird surveys of 

 the Southern California Bight area 1975-1978. Vol. 

 3 -Investigators' Reports, Part 1 - Pinnipeds of the Southern 

 California Bight, 535 p. Univ. Calif., Santa Cruz, Calif., Final 

 Report to the Bureau of Land Management, under Contract 

 AA550-CT7-367. 



^Gogan, P J. P 1977. A review of the population ecology of 

 the northern elephant seal (Mirounga angustirostris). Pro- 

 cessed Rep., 68 p. Northwest and Alaska Fish. Cent., Natl. Mar. 

 Fish. Serv., NOAA, 2725 Montlake Boulevard E., Seattle, WA 

 98112. 



^For descriptions of seasonal fluctuations in numbers of 

 northern elephant seals on land see Le Boeuf (1972) and Odell 

 (1972). 



Figure l. — Subdivision of the islands of California and north- 

 western Baja California into groups, corresponding with desig- 

 nated subpopulations of northern elephant seals (modified from 

 Le Boeuf 1977; Gogan text footnote 2; Bonnell et al. text foot- 

 note 1). 



the subpopulation as a whole. The relative contri- 

 butions of each island to the subpopulation total 

 are also presented. 



Materials and Methods 



On 8 February 1972, observers surveyed beaches 

 of all California Channel Islands (except Islas Los 

 Coronados) from U.S. Navy helicopters flying at 

 an altitude of 150 m (500 ft) and a speed of 90 kn, 

 taking large format (9 in x 9 in), near- vertical 

 aerial photographs of all elephant seals seen. 

 Counts of elephant seals were made from glossy 

 black and white prints arranged into mosaics and 

 handled in the manner described by Odell (1971). 

 When possible, animals were differentiated as 

 adult males, adult females, and pups. Counts on 

 the Islas Los Coronados were made from the beach 

 by swimmers dispatched from small boats an- 

 chored near shore. All counts represented mini- 

 mum numbers in the population because an un- 

 quantified portion is always at sea (Le Boeuf 

 1972). 



563 



