Leopard seals are at the top of their game in Antarctica. However, this refers not only to their preferred haulout places on ice floes, but also to their position in the hierarchy. This is because they have the widest range of food sources next to the orcas. But much of their way of life was still mysterious and unknown. A study by U.S. and Chilean researchers has brought to light just a few startling new facts.
Female leopard seals are up to 50 percent larger and heavier than their male counterparts, weighing on average about 454 kilograms with a length of about 3 meters. Thus, they show the greatest sex difference in species where the female is larger than the male. They also spend much more time out of the water on ice floes than the males, which is mainly due to the nursing of their offspring. The animals can spend up to ten days or more at a time on the ice without taking in food. These are just two of the results obtained by Dr. Sarah Kienle, assistant professor at Baylor University in Texas, and a team of U.S. and Chilean scientists in a study of leopard seals. All results were published in the journal Frontiers in Marine Science in August this year.
The top predator in Antarctica is still a white spot on the research map in many respects. Because to observe the animals over a longer period of time is costly and difficult due to its habitat. But Kienle and the team used new satellite-based tagging methods to learn more about the habits of leopard seals in the area on the western side of the Antarctic Peninsula. The transmitters not only provided data on whereabouts, but also stored information on the animals’ swimming and diving behavior. “This study greatly improves our understanding of the leopard seal’s lifestyle, spatial patterns and diving behavior,” explains Sarah Kienle. This is especially true in view of the changes that the western side of the Antarctic Peninsula in particular is undergoing. Animals with a high degree of adaptability and plasticity are better able to cope with such changes than highly specialized species. Especially when it comes to food
Not only penguins or seals, but also fish and especially krill are at the top of the food list for leopard seals. This plasticity helps the animals to meet their energy needs at all times. Especially females, which take care of the rearing of the young alone, need more energy. This is why the observed difference in size between the sexes is evident. But Kienle and the team discovered that leopard seals are also highly adaptable when it comes to diving. Most animals dived only briefly and not very deeply during the study period. But some animals switched to deep and longer dives. In the process, the researchers even noted a new record when one animal dove 1,256 meters deep and stayed underwater for about 25 minutes. “It’s interesting to see such differences in movements and diving behavior in a relatively small number of animals, and to me this means that leopard seals are highly flexible in their movement patterns, and that’s a really good thing in terms of adapting to changes in your environment,” Kienle adds.
Even when it comes to swimming distances, leopard seals exhibit a wide range of behavior. Between 46 and 1’669 kilometers (from the peninsula to South Georgia) the animals partly covered. However, the almost 1,700 kilometers that one animal had traveled did not surprise the researchers. For leopard seals have repeatedly made headlines in recent years when they appeared in the most unusual places. One animal, for example, made it from Antarctica to Chile’s Rapa Nui (Easter Islands), more than 5,000 kilometers away in the Pacific Ocean. Tasmania and New Zealand also receive frequent visits from leopard seals. But why the animals appear so far from their normal habitat is not clear. But the fact that they can travel such long distances, coupled with the results of the study, shows Kienle and her colleagues that leopard seals certainly have a chance of successfully meeting the challenges posed by a changing Antarctic.
Dr Michael Wenger, PolarJournal
Link to study: Kienle et al (2022) Front Mar Sci 9 (976019) Plasticity in the morphometrics and movements of an Antarctic apex predator, the leopard seal; doi.org/10.3389/fmars.2022.976019
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