Leopard seals are top predators that prey on numerous species, including pinnipeds, fishes and birds. They have a circumpolar distribution, while some individuals travel further northwards to the continents and islands of the Southern Ocean. In New Zealand an increasing number of leopard seals are sighted and some individuals have resided on New Zealand’s coastline for years.
A new study, published in the journal Frontiers in Marine Science, has found evidence of leopard seals predating on sharks, based on the remains of scat and scars on the seal bodies. While multiple diet studies have been conducted before, none ever found the species predating on chondrichthyans. The study, led by Krista van der Linde of leopardseals.org, suggests that leopard seals are part of an exclusive club of marine predators that prey on sharks.
As part of the study, the researchers, with the help of citizen scientists, “recorded 39 observations of predation and collected 127 scats (166 total records) between 1942 and 2019.” The study further stated that “predation on chondrichthyans was detected in 23.1% of observations of predation and 7.1% of scats.” The scats were taken via morphological examination and DNA sequencing.
Three main shark species were identified to be eaten by the study: the elephantfish, the ghost shark and the spiny dogfish. The study further noted that “while this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within 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,” Van der Linde told The Guardian. “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.” These findings also suggest that leopard seals actively predate on sharks and not just eat their remains. Collected poo samples further indicated that they do form a substantial part of their diet.
As leopard seals are relatively new to New Zealand and their presence becomes more common within the country, there are a few important questions asked by the researchers: Do these seals come to New Zealand to get more food as climate change affects food sources further south? And which implications does it have for New Zealand’s sharks and the local food web?
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Photography courtesy of Unsplash (cover image) and Kirsty Moffatt (on this page).