In Siberia, the freshwater mammals expertly hunt macaroni-sized amphipods
Baikal seals are fans of bite-sized portions, and this dietary quirk may be why the seals are thriving.
Found in Russia’s immense Lake Baikal, the Siberian mammals devour tiny marine crustaceans, likely using comblike teeth in a manner similar to how baleen whales feed, a new study finds.
Typically, seals eat fish and mollusks, though some southern seals, like crabeater seals (Lobodon carcinophaga), are honed eaters of krill, another type of small crustacean. For the Baikal seals, there may be big benefits to hunting amphipods. The crustaceans “are very predictable,” says marine biologist Yuuki Watanabe at the National Institute of Polar Research in Tokyo. “They form big aggregations, and they come to the surface in the nighttime.”
As many as 115,000 P. sibirica seals populate Lake Baikal, and the species is listed as “least concern” by the International Union for Conservation of Nature. This is far more abundant than seals in similar lake habitats — like the ringed seals of Lake Ladoga in northwestern Russia and Lake Saimaa in Finland, which together number a few thousand.
Watanabe has studied Baikal seals since 2003. Back then, he had evidence from depth-measuring devices mounted on the seals that showed that they reliably shifted their diving depths through the night, suggesting the animals might be following a particular food source.
And previous records of seals’ stomach contents had showed that the animals were at least occasionally eating amphipods, which make daily migrations from the depths to the shallows and back again. So in June 2018, Watanabe returned to Lake Baikal, the world’s largest and oldest freshwater lake, to see if he could gather direct evidence that the seals were feeding on swarms of amphipods.
Watanabe and colleagues caught eight seals and attached cameras and accelerometers to their backs, recording what the seals were eating, how fast they were swimming and their diving depths. The team found that the seals were rapidly snatching up individual amphipods on their night dives, as many as 154 in one descent and catching an amphipod every 2.5 seconds.
