76 



Counts of northern elephant seals, 

 Mirounga angustirostris, from 

 large-format aerial photographs 

 taken at rookeries in 

 southern California during the 

 breeding season 



Mark S. Lowry 

 Wayne L. Ferryman 

 Morgan S. Lynn 

 Robin L. Westlake 

 Fred Julian 



Southwest Fisheries Science Center 

 National Marine Fisheries Service, NOAA 

 PO Box 271, La Jolla. California 92038 



Various techniques have been used 

 to count northern elephant seals, 

 Mirounga angustirostris, at rooker- 

 ies in the United States and Mexico. 

 Individuals are customarily counted 

 by observers stationed in observation 

 blinds or on walks atop cliff-tops, 

 along the beach, or among the seals 

 (Le Boeuf, 1974; Stewart, 1989; 

 Stewart et al., 1994; DeMaster et 

 al. 1 ). Some rookeries are counted 

 from skiffs nearshore (Stewart et 

 al., 1994). Large-format (228-mm) 

 black-and-white or small-format ( 35- 

 mm) color-transparency aerial pho- 

 tographs also have been used to 

 count northern elephant seals (Bar- 

 tholomew and Boolootian, 1960; 

 Carlisle and Aplin, 1966, 1971;Odell, 

 1971; Antonelis et al., 1981; Stewart, 

 1989). In addition, counts from aerial 

 photographs have been combined 

 with information on the phenology 

 of haulout behavior to estimate el- 

 ephant seal abundance when they 

 are not censused at peak haulout 

 periods (Antonelis et al., 1981; 

 Stewart etal., 1994). 



In 1985, scientists of the National 

 Marine Fisheries Service began to 



count northern elephant seals from 

 vertical, color-transparency photo- 

 graphs taken with a large-format 

 camera. A 228-mm-format (carto- 

 graphic) camera was used in 1985 

 and 1986, but an improved system 

 was adopted in 1987 which used a 

 126-mm-format (military recon- 

 naissance) camera adjusted for low 

 altitude photography. This paper 

 describes equipment and proce- 

 dures used for counting northern 

 elephant seals from photographs 

 taken with these cameras. Counts 

 of northern elephant seals are pre- 

 sented for San Miguel Island 

 (1985-951, San Nicolas Island 

 (1988-95), Santa Rosa Island 

 (1990-95), and Santa Barbara Is- 

 land (1993-95) off the coast of 

 southern California. The method 

 used to obtain these counts was 

 validated by comparing the preci- 

 sion of counts of northern elephant 

 seals made by biologists on the 

 ground with counts made from 

 large-format aerial color-photo- 

 graphs. The counts of pups that 

 were obtained from photographs 

 taken at each island were then used 



to estimate the number of births for 

 each year. These birth estimates 

 were then compared with published 

 estimates where other techniques 

 were used in order to evaluate the 

 results obtained by each technique. 



Methods 



Photography equipment 



In 1985 and 1986, vertical photo- 

 graphs of northern elephant seals 

 were taken with a 228-mm-format 

 RC-10 cartographic camera equipped 

 with a 152-mm focal length lens. The 

 resolution of these photographs al- 

 lowed us to count seals, but the 

 image smear caused by the forward 

 motion of the aircraft reduced im- 

 age resolution slightly. This prob- 

 lem was solved in 1987 with a 126- 

 mm-format KA-45A or KA-76A 

 (military reconnaissance) camera 

 equipped with a 152-mm focal 

 length lens and image motion com- 

 pensation (IMC). The IMC and 

 camera firing sequence varied ac- 

 cording to ground speed and alti- 

 tude information to achieve a 66% 

 overlap between adjacent frames 

 (i.e. an object on the ground was 

 photographed three times per 

 pass). In addition, the hyper focal 

 distance of the KA-45A and KA-76A 

 cameras was adjusted to focus at 

 an altitude as low as 129 meters. 



The RC-10 camera was mounted 

 in a Cessna 207 aircraft ( 1985-86) 

 and the KA-45A or KA-76A camera 



1 DeMaster, D. P., R. L. DeLong, B. S. 

 Stewart, P. K. Yochem, and G. A. Anton- 

 elis. 1984. A guide to censusing pinni- 

 peds in the Channel Islands National 

 Mai mi' Sam I iiai \ and ( 'hannel Island- 

 National Park. Southwest Fisheries Sci- 

 ence Center, Natl. Mar. Fish. Serv., NOAA, 

 P.O. Box 271, La Jolla, CA. Admin. Rep. 

 LJ-84-44, 22 p. 



Manuscript accepted 19Julv 1995. 

 Fishery Bulletin 94:176-185 ( 19961. 



