Forced to swim 20 to 24 hours a day, in deep water, in order not to lose weight. Fattening is a chore for female elephant seals, which weigh an average of 350 kilograms and must continually immerse themselves in the mesopelagic zone of the ocean (that of the open sea extended between 200 and 1,000 meters deep) to feed on a sufficient quantity of young. fishes. Their only prey. To explain how it is possible that these animals manage to maintain their considerable size and survive, feeding on beings weighing less than 10 grams each, was an international team of researchers; after eight years of study, last May they published the answer in the journal Science Advances.
Scientists equipped 48 female elephant sealers with recorders and video cameras, which tracked any useful data: position, depth, jaw movement, buoyancy and preferred prey type. All to estimate the rate of fat gain in the body of the seals. And observing over five million “meals”, it was found that, on average, each one spends between 80 and 100% of the day soaking: the time it takes to make about 60 dives and be able to eat from one thousand to two thousand fish, gaining more calories than consumed.
Between 2011 and 2018, these specimens were traced during their brief migrations two months after breeding in the north-eastern Pacific Ocean. “We focused on this period because accumulating energy reserves is fundamental in their life cycles, to determine if they will reproduce in the following year and therefore to predict the dynamics of the population”, he specified. Taiki Adachi, one of the authors of the study and a researcher at both the National Institute of Polar Research and the School of Biology at the University of St Andrews, Scotland.
The results obtained indicate that female elephant sealers, lacking some characteristics typical of other similar mammals, have found a unique evolutionary path to improve diving capacity with respect to their body mass and maximize feeding opportunities. There is a close correlation between body size, prey availability and hunting skills. A circumstance that could also have negative repercussions.
Since elephant seals have adapted to only one specific pattern of foraging for food, this could put them at risk as ocean temperatures rise and possibly reduce prey availability. “Their restricted behavioral niche strongly limits their plasticity, adaptability – added Adachi – the fact that they have to move 24 hours a day to feed suggests that these seals are vulnerable to a shortage of small fish”.
Thus, the researchers intend to continue monitoring the activity of elephant seals. A work that has so far been funded by the Japan Society for the Promotion of Science, Office of Naval Research and “E&P Sound and Marine Life Joint Industry Project” of the International Association of Oil and Gas Producers. “The rate of increase of fat in their bodies – concludes Adachi – is an indicator, an important sentinel of the effects that climate change will have on ecosystems typical of the ocean depths”.
.