When a tourist boat left port in the spring of 2024, passengers probably didn’t expect to bear witness to a rare scene where sharks of two species that usually don’t occupy the same habitats flocked to a heavily decayed carcass and fed peacefully for a day. The sharks didn’t exhibit any aggressive behavior towards each other, or the tourist operators and photographers who observed the event. This kind of observation can help scientists better understand inter-species relations and social interactions between some of the oceans’ biggest hunters.
Many sharks, particularly those that live in the open oceans, are hunters rather than scavengers. Despite this, a small portion of their diet comes from scavenging, a behavior they may engage in when the opportunity arises.
Now, writing in Frontiers in Fish Science, researchers have described an unusual aggregation of sharks coming together to feed on a carcass that had decayed to mostly flesh and blubber.
“To our knowledge, this is the first study to document a feeding aggregation of tiger sharks and oceanic whitetip sharks scavenging concurrently, and peacefully, on a carcass,” said first author Dr Molly Scott, a marine researcher at the University of Hawaiʻi at Mānoa. “These species are rarely seen together in the wild because of the vastly different habitats they occupy.”
Feast in peace
Oceanic whitetips, a threatened species growing to an average of two meters in length, are solitary sharks, highly migratory, and spend most of their time roaming the oceans. This choice of habitat makes them difficult to study. During the spring and summer, however, they seasonally aggregate at Hawaii’s Big Island. Tiger sharks, a slightly bigger, more coastal species growing three to four meters on average, dwell there year-round. “It is incredibly rare for these two species to overlap in space and time,” Scott said.
In April 2024, a tourist boat sighted a heavily decayed carcass about 10 kilometers off the west coast of Big Island. Once in the water, the tourist operators could observe the feeding event for 8.5 hours. During this time, at least nine oceanic whitetip sharks and five tiger sharks were spotted.
“Even though up to 12 individual sharks were feeding intermittently from a very small, highly degraded carcass we did not observe any agonistic inter- or intra-species aggression,” Scott said. “This was surprising to me; I would assume some agonistic behaviors would exist when there are that many sharks attempting to feed around such a small carcass. But it seems all individuals knew their place in the social hierarchy.”
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First servings
Tiger sharks, most likely due to their larger size, were the dominant species. All tiger sharks, except one smaller female, and the two largest oceanic whitetips were observed most frequently feeding directly on the carcass. The smaller sharks stayed under the surface and fed on scraps drifting away. It is possible that they were attracted to the scene because of the scraps and regurgitations left behind by the larger tiger sharks, the researchers said.
There might have been other reasons for some sharks getting first servings, too. “Some individuals, like the female tiger shark, may have been shier or less bold, likely again due to her size. Also, with the other sharks having established the feeding hierarchy before the female tiger shark arrived, maybe she didn’t feel too welcome to get in on the action,” Scott explained.
The study was conducted over a relatively short time span as the carcass could not be located again the next day. Considering the size of the carcass, a lot of sharks were present, and this research could provide new insights into relationships and social interactions between sharks that don’t normally inhabit the same waters, the researchers said.
For humans, they said, it can perhaps provide a new perspective on sharks. “There were between two and three humans in the water at all times filming more than 12 sharks feeding. None of the photographers reported any scary, aggressive, or harmful interactions with the sharks,” Scott concluded. “I hope this provides a new perspective that sharks are not the human-eating predators they are made out to be.”
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