Baikal seals are followers of bite-sized parts, and this dietary quirk could also be why the seals are thriving.
Present in Russia’s immense Lake Baikal, the Siberian mammals devour tiny marine crustaceans, possible utilizing comblike enamel in a fashion just like how baleen whales feed, a brand new examine finds.
The analysis means that Baikal seals (Pusa sibirica) use a mixture of particular enamel, velocity and ability to gobble up dozens of inch-long critters referred to as amphipods on a single dive, scientists report November 16 within the Proceedings of the Nationwide Academy of Sciences.
Usually, seals eat fish and mollusks, although some southern seals, like crabeater seals (Lobodon carcinophaga), are honed eaters of krill, one other sort of small crustacean. For the Baikal seals, there could also be massive advantages to searching amphipods. The crustaceans “are very predictable,” says marine biologist Yuuki Watanabe on the Nationwide Institute of Polar Analysis in Tokyo. “They kind massive aggregations, and so they come to the floor within the nighttime.”
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Exploiting such a reliable meals source low within the meals chain, Watanabe says, might make Baikal seals extra resilient than different seals to human-driven environmental impacts resembling warming temperatures (SN: 5/1/17).
As many as 115,000 P. sibirica seals populate Lake Baikal, and the species is listed as “least concern” by the Worldwide Union for Conservation of Nature. That is much more plentiful than seals in related lake habitats — just like the ringed seals of Lake Ladoga in northwestern Russia and Lake Saimaa in Finland, which collectively quantity a number of thousand.
Watanabe has studied Baikal seals since 2003. Again then, he had proof from depth-measuring units mounted on the seals that confirmed that they reliably shifted their diving depths via the night time, suggesting the animals is likely to be following a specific meals source.
And former information of seals’ abdomen contents had confirmed that the animals had been not less than often consuming amphipods, which make every day migrations from the depths to the shallows and again once more. So in June 2018, Watanabe returned to Lake Baikal, the world’s largest and oldest freshwater lake, to see if he might collect direct proof that the seals had been feeding on swarms of amphipods.
Watanabe and colleagues caught eight seals and hooked up cameras and accelerometers to their backs, recording what the seals had been consuming, how briskly they had been swimming and their diving depths. The crew discovered that the seals had been quickly snatching up particular person amphipods on their night time dives, as many as 154 in a single descent and catching an amphipod each 2.5 seconds.
Over a single day, the seals are estimated to make 1000’s of catches. All these snacks add up. Primarily based on Watanabe and colleagues’ estimations, Baikal seals could also be getting about 20 % of their every day calorie necessities simply from amphipods.
When Watanabe examined Baikal seal skulls in museum collections and in contrast the skulls with these of different seals, he seen the cheek enamel of the Baikal animals have folded margins that give the enamel a comblike form with longer, extra developed prongs than another northern seal species. Baikal seals could also be utilizing these enamel to effectively sieve their plankton prize from the lake, expelling extra water with each gulp, the researchers say.
Mia Wege, a marine ecologist on the College of Pretoria in South Africa, was stunned such small prey might kind a serious a part of the weight loss program of a seal.
The scale of the freshwater amphipods that Baikal seals eat, she says, “is way smaller than different krill or amphipod species consumed by seals.” That is sensible although as a result of the Siberian seals themselves are among the many smallest seal species, with our bodies that may run on much less gas, Wege says.
Sooner or later, Watanabe desires to conduct feeding experiments to substantiate how the seals are utilizing their comblike chompers. He additionally desires to check the animals’ winter weight loss program, since he thinks amphipods could also be gathering beneath the lake’s winter ice, doubtlessly offering a dependable, dense feast for hungry seals. Figuring out how seasonal ice cowl influences the seals’ meals sources is of accelerating significance, says Watanabe, because the lake’s winter ice is waning as a result of local weather change.