The waters around New Zealand are very rich. This attracts not only fishermen, but also predators that have lived in the oceans for millions of years: Sharks. The enormously hardy fish prey on fish, birds, and marine mammals like seals. But the versatile hunter now seems to have found a master.
Sharks, which have lived in the world for over 450 million years, have always had the image of the feared predator. But the sharks themselves can also become prey. Predators eating other predators is rare in the animal kingdom, but it does happen.
It has long been known that orcas repeatedly attack sharks to eat their livers. Also grey sharks are washed ashore again and again without liver, particularly in South Africa.
The liver of the sharks is very oily and contains important nutrients and energy substances for the whales. Since sharks have very large livers, accounting for up to five percent of their body weight, these innards are a sought-after morsel for killer whales. But also in sperm whales, swallowed meter-long sharks in the whole, have been discovered.
And now, for the first time, proof has been provided that leopard seals feed, at least in part, on sharks.
Leopard seals are among the seals normally found around Antarctica and on some coasts of sub-Antarctic islands. And they are predators: They got their name because of their spotted fur and because they are predators that prey on small animals and fish as well as warm-blooded vertebrates like penguins and young seals of other species. But now you need to add to their diet cartilaginous fish, which include sharks.
The study was published in the journal Frontiers in Marine Science.
The researchers involved in the study evaluated fecal samples from leopard seals spanning several decades. In nine of 127 of these samples, DNA from three predatory fish species in the cartilaginous fish class was detected. Among them from ghost sharks as well as from the spiny dogfish.
The leopard seals that arrive on New Zealand’s shores are originally from the Antarctic, but are increasingly observed in New Zealand’s waters. In addition, the scientists examined visible traces on the bodies of leopard seals, which indicate a fight with sharks. These injuries provide evidence that the seals attack live sharks, not just eat their remains.
Krista van der Linde, who led the study, told Britain’s The Guardian newspaper, “We were stunned to find that sharks were on the menu.” Why leopard seals hunt sharks is not clear, she said. Because the hunt is risky.
The question of whether leopard seals have always fed on cartilaginous fish is also unclear.
According to the newspaper report, the researchers are now also asking themselves whether the seals come to New Zealand because the food supply is more varied. And whether climate change is affecting food sources further south. The most dangerous enemy of the shark is and remains man. On average, we kill 4.5 million sharks a year and many shark species are already threatened with extinction.
Link to the study: van der Linde K, Visser IN, Bout R,Lalas C, Shepherd L, Hocking D,Finucci B, Fyfe J and Pinkerton M(2021) Leopard Seals(Hydrurga leptonyx) in New Zealand Waters Predating on Chondrichthyans. Front. Mar. Sci. 8:795358
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