Among the ocean’s expanse of rarities and obscurities, scientists believe they have observed and recorded a new first; an unusual aggregation of sharks coming together to feed on a carcass that had decayed to mostly flesh and blubber.

It’s not the scavenging behaviour that has surprised scientists – as sharks, well known for being ocean hunters, aren’t averse to the scavenge – but the species involved. Because this is in an observed interaction between two species from vastly different marine habitats: tiger sharks and oceanic whitetips.

Published in Frontiers in Fish Science, the study is – to the best of researchers’ knowledge – the “first to document a feeding aggregation of tiger sharks and oceanic whitetips scavenging concurrently, and peacefully, on a carcass.”

“These species are rarely seen together in the wild because of the vastly different habitats they occupy,” said the paper’s first author, Dr Molly Scott, a marine researcher at the University of Hawaii at Manoa.

Oceanic whitetips – a threatened species growing to an average of two metres in length – are a solitary species, highly migratory, and spend most of their time in the open ocean. It’s a choice of habitat that has, to date, made them difficult to study. By contrast, tiger sharks – a slightly bigger, more coastal species – grow to four metres on average.

“It is incredibly rare for these two species to overlap in space and time,” said Scott.

So, what happened in this instance? 

It was in April last year that a tourist boat sighted a heavily decayed carcass around 10 kilometres off the west coast of Big Island. According to the tourist operators, the feeding event lasted over eight hours. It was during this time that at least nine oceanic whitetip sharks an five tiger sharks were spotted.

More surprising still, according to Scott, is that during this time “we did not observe any antagonistic inter- of intra-species aggression.” Rather, according to conclusions drawn by Scott in the research paper, “all individuals seemed to know their place in the social hierarchy.”

While the tiger sharks – most likely due to their size – were the dominant species in the interaction, all tiger sharks and the two largest oceanic whitetips were observed most frequently feeding directly on the carcass.

According to the observation, the smaller sharks stayed under the surface and fed on scraps drifting away. It’s possible, the researchers suggest, that the smaller sharks were attracted to the scene by the scraps and the regurgitations left behind by the larger sharks.

Speaking to Phys.org, Scott has listed other reasons for some of the sharks getting first helpings on the carcass, too.

“Some individuals, like the female tiger shark, may have been shier or less bold, likely again due to her size,” said Scott. “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.”

An observation such as this – in the wild – has its limitations. At under nine hours, the study was conducted over a relatively short time span and the carcass could not be located again the next day. However, the team behind the research still believe this observation could provide new insights into relationships and social interactions between sharks that don’t normally inhabit the same waters.

“There were between two and three humans in the water at all times filming more than 12 sharks feeding,” said Scott. “None of the photographers reported any scary, aggressive, or harmful interactions with the sharks.

“I hope this provides a new perspective that sharks are not the human-eating predators they are often made out to be.” 

The research paper ‘Novel observations of an oceanic whitetip (Carcharhinus longimanus) and tiger shark (Galeocerdo cuvier) scavenging event’ has been published in Frontiers in Fish Science.

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