New research led by the World Wildlife Fund for Nature New Zealand has found evidence that leopard seals eat ghost sharks. This is the first recorded example of a seal eating a shark, making seals part of a small and exclusive club of marine predators that do so.
Leopard seals (Hydrurga leptonis) are major predators known to eat a large variety of animals, including crustaceans, birds, fishes, and other pinnipeds, such as seals, sea lions, and walruses. However, this is the first time the seals were known to feed upon chondrichthyans, or fish with cartilaginous skeletons.
“From both observations of predations and scats, three chondrichthyan species or genus were identified; elephantfish (Callorhinchus milii), ghost sharks (Hydrolagus spp.) and spiny dogfish (Squalus acanthias),” write the study authors.
“While this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within our NZ records, and that certain individuals appeared to target this type of prey, indicates that these species could constitute a substantial, or important, part of the diet for some leopard seals in this region.”
“We were blown away to find that sharks were on the menu,” said study lead author Krista Van der Linde. “But then we also found elephant fish and ghost sharks were also being hunted by the leopard seals. These fish have large spines to help protect them from predators and sure enough there were wounds on the leopard seals, sometimes even big spines embedded in their faces. One leopard seal had at least 14 such wounds.”
Van der Linde and her colleagues believe that leopard seals are opportunistic predators, arriving from Antarctica to New Zealand in order to find a more varied diet and to feast “on whatever they can get their jaws on.” It is not yet clear whether eating sharks is a new behavior, caused by changed patterns of migration, or if it was a regular part of these seals’ diet since a long time ago.
Predators feeding on other predators remains though a peculiar and quite rare phenomenon. Until recently, scientists thought that only orcas eat sharks. “To know there is another marine mammal also munching on sharks, well, that has implications for the whole food web and our understanding of how it all is interlinked,” Van Der Linde said.
The study is published in the journal Frontiers in Marine Science.