Southern Elephant Seals’ Choice of Prey Helps Them Hunt in Dark

Bioluminescence helps southern elephant seals in search of their prey in the dark, suggests a new study.

Southern elephant seals are the world's largest seals and they weigh around two to five tons. They are capable of diving deeper than 4,900 feet (1,500 meters) under the water while traveling long distances. As the oceans get deeper, there is absolute darkness with no light for visibility, reported LiveScience.

Marine mammals such as whales, dolphins and penguins have adapted themselves to such dark environments to find their prey. While whales and dolphins use echolocation to identify their prey, penguins depend on their capability to catch the scent of their prey.

Seals are known to spend very little time on the surface, and that too only to breathe, while they spend more time in the deep sea waters. They spend as many as ten months in the Indian Ocean coming ashore only to breed and molt.

While southern elephant seals do not have a well-developed echolocation system, they are known to use their vision to find their prey. However, it wasn't certain how the southern elephant seals manage to locate their food in the dark deep sea waters.

A team of researchers led by Jade Vacquié-Garcia, a marine biologist at the Center for Biological Studies of Chize in France, tagged four female southern elephant seals in the southern Indian Ocean with light detectors and electronic devices to monitor their diving behavior including the length and depth of their dives. They observed a total of 3,386 dives and detected bioluminescence events.

They found that the southern elephant seals fed primarily on lanternfish. Lanternfish are bioluminescent, wherein they have luminous patches that emit a glow naturally. The glow helps the southern elephant seals to identify their prey in the dark ambience. The seals also use the glow as a means to communicate with other members of their species.

Earlier studies have shown that southern elephant seals have adapted to low intensity light with peak sensitivity to blue light that the bioluminescent lanternfish emits.

The new study pointed out a positive relation between the bioluminescent events from marine organisms and the foraging activity of the southern elephant seals in the deep waters where there was no effect of natural light.

Researchers are planning to further study the changing patterns in seals' movements , if any, in response to the bioluminescent events when approaching a predator.

The findings of the study, "Foraging in the Darkness of the Southern Ocean: Influence of Bioluminescence on a Deep Diving Predator," are published in the journal PLoS ONE.