Alison Cutler
Tue, December 21, 2021
The hunter has become the hunted off the shores of New Zealand, a new study shows. Leopard seals have added sharks to their menu of seafood snacks, researchers found.
Scientists identified remnants of ghost sharks, spiny dogfish, and elephant fish eaten by seals, which are all classified as sharks, or chondrichthyan species.
The study, which can be found in the Frontiers in Marine Science Journal on Dec. 16, was the first published study to record leopard seals eating any type of shark.
“We were blown away to find that sharks were on the menu, but then we also found Elephant fish and Ghost sharks were also being hunted by the leopard seals,” Krista van der Linde from the World Wildlife Fund for Nature New Zealand and a co-author in the study told Newsweek.
Data collection and examination for the study included:
geographic records of where Leopard seals hunted off the coasts of New Zealand
observed predation where researchers would identify a seal and photograph it’s prey for visual identification
fecal matter (scat) from Leopard seals
The study leveraged the work of citizen scientists as well as researchers from Leopardseals.org. In total, the study observed 39 incidences of predation. Nine of the 39 were predation on sharks, the study said.
Nine fecal samples also showed that leopard seals were preying on sharks.
According to the observations, seals were found to prey on shark species more often in the spring and the winter. Adding sharks to the leopard seal palate could pose a prey competition between orcas and leopard seals.
Dangers of shark hunting
Hunting sharks doesn’t come without consequences though, scientists say.
“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 told Newsweek.
Injuries may be expected out of an inexperienced group of seals, like juveniles who haven’t learned their lesson about what and what not to target, but the data indicates the injuries weren’t just a lack of hunting knowledge among the seals.
Out of all the seals recorded to hunt the sharks, 11 were reported as adults, and 6 as juveniles. Data also noted that when sex could be identified in the study, 11 females were documented hunting sharks, and 3 males were identified.
The study examined how deep each shark typically resided in the waters, which indicated that leopard seals could be diving deeper than normal to target certain sharks, specifically the ghost shark. It also noted that leopard seals might steal shark remains from other seal species, like the Antarctic Fur Seal, which is known to eat sharks.
Yet another possibility, researchers offer, is that leopard seals are scavenging commercial fishery discards for sharks.
Why hunt sharks?
But why? Leopard seals are known for their maneuverability and wide prey selection, from krill to fish to birds and even penguins, which some may know from the anxiety-inducing scene involving the leopard-seal antagonist in the 2006 film “Happy Feet.” So what’s the motivation from killing prey, to predators — to the point that they would risk dozens of wounds and infection to finish one off?
“While this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within our NZ records indicates that.... these species could constitute a substantial, or important, part of the diet for some leopard seals in this region,” researchers wrote.
For future examination, the scientists noted that environmental conditions, including changes in human population, interaction and pollution, should be taken into consideration when theorizing why animals hunt the creatures they do, and how it impacts predator-to-prey relationships.
Leopard seals have been in New Zealand since the 1860s, according Leopardseals.org, and are protected by law under the Antarctic Treaty.
It is an offense under the Marine Mammals Protection Act of 1978 to “disturb, harass, harm, injure or kill” a leopard seal, and offenders could face up to two years in prison, or be fined up to $250,000.
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