Hunting tactics comparison of southern elephant seals vs. fur seals
From the beaches of the Southern Ocean, seals and sea lions, typical of the Kerguelen archipelago, head for the polar seas to fill their bellies with fish. Each with its own hunting method.
Sharp fangs planted in the flesh of lanternfish. Wide mouths sucking in small prey. The pinniped mammals compete for the resources of the Southern Ocean, but with very different tactics. Last May, researchers at the Centre d’Études Biologiques de Chizé presented two papers published in the Marine Ecology Progress Series and the Journal of Experimental Biology showing that the smaller fur seal is more proactive, while the larger elephant seal is more reticent. Agile sea lions develop tactics based on their ability to pursue prey. Elephant seals, on the other hand, hide in the depths of the ocean to surprise their prey. These flipper-footed hunters beat the field, opting for rowdiness in the first case, in search of face-to-face encounters; for the second, waiting in ambush is the key.
Elephant seals weigh several hundred kilos up to a few tons. This massive creature undulates its fins at the back of its body and detects its prey some ten meters away. Just as they spot it, it stops swimming, interrupts all movement and glides towards its prey, which it sucks in with a wide-open mouth and a rapidly receding tongue. “It seems to work because we’ve noticed that prey flee at the last moment”, explains Mathilde Chevallay, who is completing her thesis on the subject.
Fish are sensitive to movement in the water. They detect vibrations using their lateral lines. When hunting, sea lions like elephant seals move slowly through the water, thereby limiting disturbance. “Fur seals spot their prey less in advance, just one second before capture”, explains the researcher. In this game of cat and mouse, the fur seal and fish detect each other simultaneously, just a few dozen centimetres apart. The fur seal then sets off in pursuit of its target. In an active hunting mode, it has very little time to grip the fish.
“Their pectoral flippers are highly developed and very muscular. Weighing in at around 30 kilos each, they give sea lions excellent acceleration and manoeuvrability,” explains Mathilde Chevallay. Although skillful, these marine mammals only dive to a depth of 50 metres, whereas elephant seals venture to depths of over 500 metres. “More than 800 metres for very good divers”, says the biologist. At these depths, the oceanic species are best suited to smaller, slower-moving prey. Their sliding stalking tactic is less calorie-intensive, but doesn’t prevent them from eating some 1,000 catches a day. On the surface, sea lions can quench their thirst for energy with larger fish. In the end, there’s something for everyone.
Responsive or stealthy, these two predators learn to hunt on their own. Each individual takes the plunge and disperses from their very first days at sea, without being able to rely on the most experienced to learn their trade. As a result, different tactics are sometimes adopted. In Argentina’s Valdés Peninsula, three of the 15 elephant seals studied by the Chizé researchers target schools of fish that they could catch by performing a backward pirouette before capturing them. “And it works – we can see they’re putting on weight,” confirms Mathilde Chevallay. This has never been observed with Kerguelen individuals.
“Have they met more shoals in the course of their learning?” the researchers wonder. As fur seals in South Georgia eat more krill, should we expect them to behave differently? How the Austral pinnipeds develop their hunting tactics is still unknown, attracting the curiosity of the biologists at Chizé.
Camille Lin, Polar Journal AG
Link to the studies:
- Chevallay, M., Guinet, C., Goulet, P., Dot, T.J. du, 2024. Hunting tactics of southern elephant seals Mirounga leonina and anti-predatory behaviours of their prey. Marine Ecology Progress Series 736, 167–179. https://doi.org/10.3354/meps14582 .
- Chevallay, M., Guinet, C., Goulet-Tran, D., Jeanniard du Dot, T., 2024. Sealing the deal – Antarctic fur seals’ active hunting tactics to capture small evasive prey revealed by miniature sonar tags. Journal of Experimental Biology 227, jeb246937. https://doi.org/10.1242/jeb.246937 .
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