How these sharks are similar to their great white counterparts

By Stephen Beech via SWNS

Basking sharks are warm-blooded - just like great whites, reveals new research.

Around 99.9 percent of fish and shark species are “cold-blooded” - meaning their body tissues generally match the temperature of the water they swim in.

Now a new study led by Irish scientists has discovered the mighty basking shark - the world's second biggest fish species - is a one-in-a-thousand exception.

Instead, they keep the core regions of their bodies warmer than the water like the most athletic swimmers in the sea such as great white sharks, mako sharks and tuna.

Great white, makos tuna are so-called “regional endotherms” and are all fast swimming, apex predators at the top of the food chain.

Scientists have long believed that their ability to keep warm helped with their athletic predatory lifestyle, and that evolution had shaped their physiology to match their requirements.

However, an international team led by Trinity College Dublin researchers, has now shown that gentle, plankton-feeding basking sharks are also regional endotherms - despite having very different lifestyles to white sharks and tunas.

The researchers say the surprising discovery has implications for conservation, as well as raising several ecological and evolutionary questions.

Study lead author Haley Dolton said: “The basking shark is a shining example of how little we know about shark species in general.

"That we still have lots to uncover about the second biggest fish in the world – such a huge, charismatic animal that most people would recognize it – just highlights the challenge facing researchers to gather what they can about species to aid in effective conservation strategies."

Basking sharks gained legal protection in Irish waters just last year, with the species having undergone a "significant" decline in numbers throughout the North East Atlantic over the last century.

Dolton, a Ph.D. Candidate in Trinity’s School of Natural Sciences, added: “Regional endotherms are thought to use more energy, and possibly respond differently to ocean warming than other fish species.

"So lots more work will need to be done to work out how these new findings regarding an endangered species might change previous assumptions about their metabolism or potential distribution shifts during our climate crisis, which is something marine biologists are focusing on as our planet and its seas continue to warm.

“Hopefully this kind of research will continue the momentum needed to effectively protect these incredible animals in Irish waters and further afield.”

The research team, which also included scientists from the Zoological Society of London (ZSL) and the University of Southampton, first conducted dissections of dead basking sharks that washed up in the UK and Ireland.

They found that the sharks have cruise-swimming muscles located deep inside their bodies as seen in white sharks and tunas. In most fish the “red” muscle is instead found toward the outside of the body.

The researchers also discovered basking sharks have strong muscular hearts that probably help generate high blood pressures and flows.

They explained that most fish species have relatively “spongy” hearts, whereas basking shark hearts are more typical of the regional endotherm species.

Next, the researchers designed a new low-impact tagging method to record body temperature of free-swimming basking sharks off the coast of County Cork.

The team was able to get close enough to eight-meter (26ft) basking sharks to safely deploy the tags, which recorded muscle temperature just under the skin for up to 12 hours before they automatically detached and were collected by the researchers.

The findings, published in the journal Endangered Species Research, revealed that basking shark muscles are consistently elevated above water temperatures, and to almost exactly the same extent as their regionally-endothermic predatory cousins.

Study senior author Nicholas Payne, Assistant Professor in Trinity’s School of Natural Sciences, said: “These results cast an interesting new light on our perception of form versus function in fishes because until now we thought regional endothermy was only found in apex predatory species living at high positions in the marine food web."

He added: “Now we have found a species that grazes on tiny plankton but also shares those rather uncommon regional endotherm features, so we might have to adjust our assumptions about the advantages of such physiological innovations for these animals.

“It’s a bit like suddenly finding that cows have wings.”