Female southern elephant seals (Mirounga leonina) spend most of the year — 10 months — at sea, foraging for lanternfish and cephalopods. Unlike some predators, these seals need to return to the ocean’s surface to breathe between dives for their prey, so efficient diving behavior is key to successful foraging.
In a recent study, Yves Le Bras and colleagues from the Centre d’Etude Biologiques de Chizé, France, investigated whether elephant seals change their diving behavior when prey are more abundant. The researchers fitted nine female southern elephant seals in the Indian Ocean with loggers that recorded data including location, depth, acceleration and horizontal speed.
The researchers found that that diving seals made two major adjustments when encountering prey at high rates. First, the seals dove at steeper angles, reducing the transit phases of the dives and so making them more efficient. Second, the seals were more sinuous at the bottom phase of dives, reducing the horizontal travel distance at the surface. This may counteract horizontal displacement from water currents, helping the seals stay in favorable prey patches.
While only nine seals were included in the study, the researchers suggest that their findings may apply to other air-breathing divers such as Antarctic fur seals, that also eat small prey, such as fishes or crustaceans. In contrast, air-breathing divers such as Weddell seals that favor large prey such as Antarctic toothfish may return to the surface to feed. This work may also help predict how changes in prey distribution might affect predator populations.
Image Credit: Christophe Guinet
Citation: Le Bras Y, Jouma’a J, Picard B, Guinet C (2016) How Elephant Seals (Mirounga leonina) Adjust Their Fine Scale Horizontal Movement and Diving Behaviour in Relation to Prey Encounter Rate. PLoS ONE 11(12): e0167226. doi:10.1371/journal.pone.0167226