• Tue. Feb 27th, 2024

Discovering that sharks are warm bodies is like “discovering that cows have wings”.

Discovering that sharks are warm bodies is like “discovering that cows have wings”.

Despite their more sedentary lifestyle, researchers have found that basking sharks are as warm-bodied as great whites.

An international team led by scientists from Trinity College Dublin says the “surprising” discovery has implications for the conservation of the species, which was granted legal protection in Irish waters last year.

Their findings have been published in the international journal, Endangered species research.

Scientists explain that about 99.9% of fish and sharks are “cold-blooded,” meaning that their body cells are usually adapted to the temperature of the water in which they swim.

However, “a strong basking shark is one in a thousand”, they say.

“Basking sharks, like the most athletic swimmers in the ocean, such as great white sharks, mako sharks and tunas, keep their cores warmer than the water,” she states.

Great whites, mako sharks, and tunas are all fast-swimming “apex predators” known as “local endotherms” at the top of their food chain.

It’s long been believed that this ability to maintain warmth aided their “athletic predatory lifestyle” – evolution shaped the physiology to suit their needs.

The research team, which included scientists from the University of Pretoria, the Marine Biological Association, Queen’s University Belfast, the Zoological Society of London, the University of Southampton and Manx Basking Shark Watch, first dissected dead sharks washed up in Ireland and Britain.

They found that sharks have cruise swimming muscles located deep within the body, similar to those seen in white sharks and tunas; In most fish this “red” muscle is found on the outside of the animal.

They also found that sharks have strong muscular hearts that help generate high blood pressure and flow. Most fish species have relatively “spongy” hearts, while basking shark hearts are more common among endemic endotherm species.

The team says it has designed a new low-impact tagging method to record the body temperature of basking sharks swimming freely off the coast of Co Cork.

The researchers say basking sharks were able to get close to 8m to safely deploy the tags, which recorded subcutaneous muscle temperatures for up to 12 hours before being automatically detached from the animals and collected.

“These tags reveal that basking shark muscles are consistently elevated above water temperatures, and to about the same extent as their endothermic cousins,” they state.

The study’s lead author Haley Dalton, a PhD candidate in TCD’s School of Natural Sciences, said the basking shark was “a shining example of how little we know about common sharks”.

“We still have so much to discover about the world’s second-largest fish — such a large, charismatic animal — that most people will recognize — highlighting the challenge researchers face in gathering what they can about the species to aid in effective conservation strategies,” Dalton said.

“Local endotherms are thought to use more energy and are likely to respond differently to ocean warming than other fish species,” continued Dalton.

“Thus, more work is needed to understand how these new discoveries about an endangered species might change previous assumptions about their metabolism or potential distribution shifts during our climate crisis.

Senior author of the study Nicholas Payne, Assistant Professor in TCD’s School of Natural Sciences, said, “It sheds an interesting new light on our understanding of form versus function in fish, as local endothermy is only found in apex predator species that occupy high positions in the marine food web”.

“Now that we’ve discovered a species that grazes on small plankton but also shares rare local endotherm traits, we may need to adjust our assumptions about the benefits of such physiological innovations for these animals,” Payne said.

“It’s like suddenly discovering that cows have wings,” he said.

Haley Dolton is funded by the Irish Research Council, supported by the Fisheries Society of the British Isles and Dr. Nicholas Payne was also funded by Science Foundation Ireland.

The journal article can be read here: https://www.int-res.com/abstracts/esr/v51/p227-232/. A PDF copy is available upon request.

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