The amazing sensory map of the elephant seal

Capable of traveling an average of nearly 10,000 km over 240 days across the northeastern Pacific to reach feeding sites, female elephant seals of the species Mirounga angustirostris Always return to the same breeding grounds to give birth on the California coast. If not all females travel the same distances, they nevertheless return synchronously to the breeding sites at the beginning of the calving season, at the end of January. Roxanne Beltran, a biologist at the University of Santa Cruz in California, and her colleagues have identified specific elements that would explain this amazing navigational ability. The data from their study is consistent with the hypothesis that females are able to synchronize their return by perceiving the geographical distances they travel during their journey at sea.

Many marine animals such as birds, turtles, or even whales make annual movements between feeding and breeding sites with pinpoint accuracy in programming the return migration. However, it is still not well understood when and why these animals decide to move. It is known that the decision for the return trip depends in part on the energy gain in the foraging areas and the energy costs associated with the trip. But the researchers showed that migrants can also combine spatial information to assess their position relative to a breeding site as well as temporal information to work out when to return based on distance traveled. Do elephant seals use these energetic and spatiotemporal characteristics to locate themselves in the ocean?

Researcher Roxanne Beltran and students Milagros Rivera and Natalie Storm search for elephant seals that were uniquely identified on a breeding beach.

© Dan Costa

Using satellite data, Roxanne Beltran and her colleagues followed 108 females, between 2004 and 2015, to determine the date when their daily movements definitively began toward the birthing beach, located on the island of Año Nuevo, California. They also used an indirect indicator of the amount of body fat to see if the decision to drop was related to the individuals’ physical condition.

Surprisingly, elephant seals would rotate based on their distance from shore, but this decision was not related to their body condition. Females who had traveled the greatest distance started returning early in order to have enough time to return to the breeding site, while females who had not traveled that far started returning later. These data suggest that elephant seals will have a spatio-temporal representation of their location in the marine ecosystem, allowing them to modify their movements with respect to their final destination. “A potential confounding factor is the age, and therefore experience, of individuals. It is conceivable that older or seasoned females would travel farther distances because they better estimate the time required to return to Earth for procreation. However, it is still assumed that they have this appreciation for distances that they can that evolve over the course of a female’s life,” adds Mathieu Autier, an ecologist at the Mammal and Seabird Observatory (Pellagis Observatory), at the University of La Rochelle-CNRS.

Despite this new observational data, the sensory mechanisms involved in seals’ ability to assess their location remain undefined. Such navigation performance can be based, for example, on a geomagnetic, celestial, acoustic, or even olfactory basis.

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