Forget Sharknado. Based on a new study, the aquatic creature you don’t want to see falling from the sky isn’t sharks – it’s seals. Seals are attacking and eating sharks off the coast of South Africa and marine biologists are trying to figure out why.
Cape fur seals (Arctocephalus pusillus) and blue sharks (Prionace glauca) normally leave each other alone in the tropical waters off the South African coast. Each feed on smaller fish, squid and crustaceans and there seem to be plenty for both species to survive without nibbling on each other. Fur seals are a little smaller than blue sharks but these sharks don’t seem to find the seals as tasty as great whites do. While groups of fur seals have been known to surround great white sharks, it seems to be a defensive maneuver designed to scare the predator away.
In 2004, dive boat operator and marine photographer Chris Fallows first witnessed a fur seal attacking a blue shark off the coast of Cape Town. He saw a larger attack by multiple seals on five blue sharks in 2012. After other reports came in, Fallows joined with marine experts to study the behavior and possible causes and recently released their findings in the African Journal of Marine Science.
Dr. Neil Hammerschlag, a marine biologist at the Rosenstiel School of Marine and Astmospheric Science in Florida, observed that the seals attack the sharks from underneath and eat their guts, most likely because those organs give them the most energy.
OK, so shark guts are tasty and better than Red Bull. Is that a good enough reason for the fur seals to attack them? Hammerschlag thinks the seals may also be eliminating the blue sharks from the competition for fish, which are becoming increasing scarce due to over-fishing and pollution.
Hammerschlag warns that this behavior is upsetting the natural balance of the sea.
The consumption of large sharks by a Cape fur seal is a departure from the prevalent view of this species’ diet, which is generally reported to consist of a diverse diet of small fish species, cephalopods and birds … These observations are important not just for understanding the interactions between these two species but more broadly for their implications in understanding the trophic ecology of pinnipeds – many populations of which have increased while numerous shark populations have declined.
Should we be worried? Anytime the balance of nature is upended, it’s a cause for concern. Sharks are becoming more scarce by the day. And who wants to see a movie about killer seals?