Elephant Seal Researchers Bullish on Male Tagging

Despite their epic battles in the surf zones of rookery beaches, male elephant seals are less interesting than females; at least from the standpoint of how they use the dynamic ocean. Studies conducted a decade ago revealed that unlike the female elephant seals who venture out to sea to forage, males traveled north to the Aleutian Islands in a single, highly directed journey. This behavior seemed to be the norm for this population of animals, and TOPP scientists determined that the foraging travels of the females would yield more interesting data.

Then, three years ago, researchers led by in the field by Dan Crocker, of California State University Sonoma, deployed over twenty tags on male elephant seals in three colonies on the Pacific Ocean side of Baja California. Over the course of two seasons, researchers tagged bulls on Guadalupe, Cedros and San Benitos Islands. "The question," says Crocker, "was whether these males would use the same Alaskan foraging grounds as their Año Nuevo counterparts." Given the enormous extra distance between this destination and the southern rookeries, it seemed unlikely that the animals would have sufficient transit time to make the trip worthwhile, so they expected to see different behavior. Just how different the behavior would turn out to be surprised everyone.

The Mexican males showed enormous variability within the breeding populations, doing "things we'd never seen before," recalls Crocker. Some foraged locally, staying within 50 kilometers of their rookeries. Others foraged over sea mounts, or traveled up and down the coast feeding in more than one location. Still others actually did travel all the way to Alaska. What did this mean?

TOPP researchers wanted to take a second look to see whether the behavior they'd seen from their Año Nuevo population of males would show any changes that might reflect changes in the ocean. "And," adds Crocker, "we knew we'd get great data for the oceanographers because the males make these nice transects across the Pacific." While this later point is – as Crocker describes "gravy," the benefit is significant. "We get between 500 to 1,000 CTD profiles from each animal," explains Crocker. Oceanographers traditionally rely upon boats to gather this kind of data, and the expeditions are expensive. TOPP's "animal oceanographers" can provide the oceanographic community with a rich cache of data while yielding answers to questions of vital interest to biologists.

TOPP pinniped researchers hope to deploy about ten tags in total on Año Nuevo males, Last May the team tagged four males, and are currently analyzing the tracking data. So far, there are hints that the males may be just as interesting as their mates! 

-- By Diane Richards