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September 2023
By: Mackenzi Moyes
Recently, scientists have discovered a shocking, and rather ground-breaking fact about basking sharks. Let’s take a look!
Approximately 99.9% of all fish and shark species are - “cold-blooded” - meaning their body tissues generally match the temperature of the water they swim in. Recently, research discovered the mighty basking shark is a one-in-a-thousand exception. Instead, basking sharks keep their bodies warmer than the water they live in, like tuna, mako sharks and great white sharks.
Basking sharks (Cetorhinus maximus) have long been considered classic ectotherms, meaning their body temperature is primarily influenced by the surrounding environment. These slow-moving giants, often referred to as gentle giants due to their docile nature, are filter feeders that typically inhabit temperate and cold oceans. Their impressive size, reaching up to 40 feet in length, has led researchers to believe that they were able to maintain a suitable body temperature solely through their massive bulk and insulation provided by their thick skin.
"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 recognise it -- just highlights the challenge facing researchers to gather what they can about species to aid in effective conservation strategies.
Only just last year did the basking shark receive legal protection in Irish waters, after the species undergone significant population declines throughout the NE Atlantic in the last century.
They found the sharks have cruise-swimming muscles located deep inside their bodies as seen in white sharks and tunas; in most fish this ‘red’ muscle is found toward the outside of the animals. The results showed clear evidence of regional endothermy, which the authors say has implications for conservation, as well as raising ecological and evolutionary questions.
"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," said Nicholas Payne, study lead author and assistant professor at Trinity College Dublin.
They also discovered basking sharks have strong muscular hearts that probably help generate high blood pressures and flows. Most fish species have relatively “spongy” hearts, whereas basking shark hearts are more typical of the regional endotherm species.
Next, the team designed a new low-impact tagging method to record body temperature of free-swimming basking sharks off the coast of Co Cork, Ireland. Researchers were able get close enough to 8 m basking sharks to safely deploy the tags, which recorded muscle temperature just under the skin for up to 12 hours before they automatically detached from the animals and were collected by the researchers.
The revelation of warm-bodied basking sharks adds an intriguing layer to the conservation efforts aimed at protecting these magnificent creatures. Understanding the specific environmental conditions that favor the development of warm-blooded traits could aid in identifying critical habitats for these unique individuals. Furthermore, this discovery opens up a new avenue of research into the genetics and molecular mechanisms that underpin this extraordinary adaptation.
References
Meteored, ‘A one-in-a-thousand exception: basking sharks found to be partially warm-bodied
Science Daily, ‘Shark shock: Scientists discover filter-feeding basking sharks are warm-bodied like great whites’ https://www.sciencedaily.com/releases/2023/07/230720124901.htm
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