May 17, 2012
Elephant Seal Study Reveals Previously Unknown Behaviors
Brett Smith for RedOrbit.com
Researchers at the University of California - Santa Cruz (UCSC) have used tracking devices to learn more about previously unknown behaviors of Northern elephant seals.Their study, published May 15 in the journal PLoS ONE, used satellite tracking devices to follow the migratory, breeding, and predatory behaviors of the Pacific dwelling mammals. The information gathered by the researchers showed almost 300 seals traveling throughout the northeast Pacific Ocean in search of food and mating partners.
"This work is unprecedented in terms of the number of animals tracked," said Daniel Costa, leader of the elephant seal research group at UCSC. "For the first time we can truly say that we know what the elephant seal population is doing.”
The tracking data showed female elephant seals prefer to reside in a particular section of the Pacific – a border zone between two rotating currents, or gyres. The colder sub-polar gyre brings nutrient-rich water down from the arctic where it meets the sub-tropical gyre that churns warmer water and a vibrant food web up from areas just north of the equator.
A previous study by the same research group published last year showed that this boundary between warm and cold water flows creates an ideal habitat for the seals´ prey and draws these and other predators with its plentiful food supply.
"The highest density of seals is right over that area, so something interesting is definitely going on there," said Patrick Robinson, co-author of the study.
The research team also gained a better understanding of the female elephant seals´ migratory cycle that appears to be geared toward reproduction. The females were observed making two trips for food foraging per year, after the breeding season in the early spring and from June to January just after molting. Many of these trips included the seals diving to extreme depths of greater than a mile below the surface.
The UCSC team worked in conjunction with researchers in Mexico to tag elephant seals at Islas San Benito, which is 1,150 kilometers (690 miles) southeast of where the American team is based.
"A lot of those animals travel much further to get to foraging areas in the north, so they might spend an extra week traveling, and we wanted to see how that affects them," Robinson said. "The animals from San Benito that do go up to feed at the boundary zone do fine, but we also found that many of them stayed closer to home, feeding along the continental shelf, and they were successful too."
The scientists also found that the amount of food located by female elephant seals during these foraging migrations affects the birth weight and health of their seal pups. This was done through the monitoring of the individual seal´s weights when they returned to the rookery, or breeding area. In addition to having their weights taken, tagged elephant seals also had a sample of blood drawn.
The seal tracking devices also provided large amounts of new data on the conditions of deep Pacific waters. The sophisticated tags were able to measure temperature, depth, and water salinity as the seals went about their normal activities. This data was formatted and uploaded to the World Ocean Database for use by oceanographers around the world.