January 15, 2008. HSWRI scientist Dr. Brent Stewart arrived at San Miguel Island, California, this afternoon, after spending a week at San Nicolas Island. The northern elephant seal breeding season is in full swing, and Brent will be busy for the next few months traveling to and from the islands to document elephant seal births and determine the fate of seals tagged in previous seasons. Dr. Stewart, Dr. Pam Yochem (HSWRI) and colleagues at NOAA Fisheries have collaborated on studies of the population biology, foraging ecology and health of elephant seals and other pinnipeds at the Channel Islands for nearly 30 years.
A new documentary “A Seal’s Life: The Story of the Northern Elephant Seal” is playing in limited release this month, including showings at educational venues such as the Birch Aquarium at Scripps Institution of Oceanography, UC San Diego. The film details the extraordinary journey that elephant seals have taken for hundreds of thousands of years. Twice a year along the west coast of North America, these animals set out alone on a nearly impossible roundtrip migration across the vast expanse of the North Pacific Ocean. For months they remain at sea, swimming thousands of miles while diving relentlessly to unimaginable depths in search of food. National Geographic Explorer-in-Residence Dr. Sylvia Earle, a renowned ocean explorer and marine conservation advocate, narrates the film. HSWRI scientist Dr. Brent Stewart and NOAA Fisheries colleague Dr. Robert DeLong were the first to describe the eight to 10 month duration, long-distance, double migrations by adult northern elephant seal males and females. Their discovery, published in the Journal of Mammalogy, was profiled in Discover magazine’s January 2006 issue as one of the top 100 science stories of 1995. Drs. Stewart and DeLong also discovered that adult males and females segregate nearly completely while moving into the central Pacific (females) and north to the Gulf of Alaska (males) to forage. Both sexes dive continuously while at sea, foraging routinely at depths of 1500 to 3000 feet below the surface and occasionally to 5000 feet or more. Dives last about 15 to 20 minutes on average but may last up to two hours on occasion. The northern elephant seal was hunted for the oil in its blubber and was presumed extinct by the late 1800s. A few survived and the population has been increasing at exponential rates for decades, with many tens of thousands of pups now born in California each year. For more information see: Stewart, B. S. 1997. Ontogeny of differential migration and sexual segregation in the northern elephant seal, Mirounga angustirostris. Journal of Mammalogy 78:1101-1116. Stewart, B. S. 1996. Uncommon Commuters. Natural History Magazine. February 1996. Stewart, B. S. and R. L. DeLong. 1995. Double migrations of the northern elephant seal. Journal of Mammalogy 76:196-205. DeLong, R. L., Stewart, B. S., and Hill, R. D. 1992. Documenting migrations of northern elephant seals using daylength. Marine Mammal Science 8:155-159. DeLong, R. L., and Stewart, B. S. 1991. Diving and foraging patterns of northern elephant seal bulls. Marine Mammal Science 7:369-384.