Pinniped Aerial Surveys

Northern elephant seals on the beach at Point Bennet, San Miguel Island, California, on February 3, 1990. Shown here is a portion of a 126mm-format aerial photograph taken from an aircraft flying at 850 feet altitude.

The Pinniped Aerial Surveys Project conducts censuses of five species of pinnipeds (i.e., seals, sea lions, and fur seals) for monitoring trends and abundance of populations found in the United States. Pups and other age/sex classes are counted from color photographs taken at rookeries and haulouts during aerial surveys of islands and the mainland coast of California. Surveys are conducted in February for elephant seals (Mirounga angustirostris), May through July for harbor seals (Phoca vitulina richardii), and July for California sea lions (Zalophus californianus), Steller sea lions (Eumetopias jubatus), and northern fur seals (Callorhinus ursinus). Surveys are also conducted opportunistically at selected California sea lion rookeries in Baja California, Mexico during late-July and early-August.

Mark Lowry counts pinnipeds on 126mm-format aerial photographic images.

The project is assisted by the Photogrammetry Program, within the Marine Mammal and Turtle Division (PRD), which provides photographic equipment and maintenance of the camera system utilized by the Coastal Marine Mammal Program's (CMMP) Pinniped Aerial Surveys Project. High resolution color photographs of pinnipeds are taken with a 126mm-format (5-inch-format) KA-76 camera mounted internally aboard the belly of a twin-engine, high-winged Partenavia PN68-observer model aircraft. The geographical position of each photograph is recorded by linking the camera to a computer and Global Positioning System (GPS). Aerial photographic surveys in Baja California, Mexico utilize the same camera system, but are conducted with a Hughes 500D helicopter carried aboard the NOAA Ship David Starr Jordan. Surveys are conducted at 700 to 850 feet altitude with a 152 mm (6 inch) focal-length lens-cone on the camera, however, when pinnipeds are found with seabirds at protected seabird colonies (such as at the Farallon Islands in central California) then photographs are taken at 1400 feet altitude with a 305 mm (12 inch) focal-length lens-cone on the camera. The pinniped species being censused is then counted from the photographs as a biologist looks through a 7-30X zoom binocular microscope as the color transparency photograph is illuminated on a light table. Animals of each age/sex class are marked on a clear acetate plastic overlay with different colored pens as each animal is counted to assure that all are counted and to prevent double counting the same animal.

The principal investigator is Mark Lowry of the California Current Marine Mammal Assessment Program (CMAP) at SWFSC. Mark conducts most of the field work associated with this project, and is sometimes assisted during surveys by members of CMMP and other programs within MMTD. The data collected from this project is used in U.S. marine mammal stock assessment reports (SAR's) and for other manuscripts. Further details of this project and data can be obtained from the following reports:

Counts of California sea lion pups in the United States show that the population is increasing.

Lowry, M. S. and W. L. Perryman. 1992. Aerial photographic census for California sea lion (Zalophus californianus) pups at San Miguel Island, California for 1987-1990 and San Nicolas Island, California for 1990. National Marine Fisheries Service, Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92038, Administrative Report LJ-92-19. 19 pp.

Lowry, M. S., W. L. Perryman, M. S. Lynn, R. L. Westlake, and F. Julian. 1996. Counts of northern elephant seals, Mirounga angustirostris, from large-format aerial photographs taken at rookeries in southern California during the breeding season. Fishery Bulletin, U. S. 94:176-185.

Lowry, M. S. 1999. Counts of California sea lion (Zalophus californianus) pups from aerial color photographs and from the ground: a comparison of two methods. Marine Mammal Science 15:143-158.

Lowry, M. S. 2002. Counts of northern elephant seals at rookeries in the Southern California Bight: 1981-2001. NOAA Technical Memorandum NMFS: NOAA-TM-NMFS-SWFSC-345. 63 pp.