Basking shark (Cetorhinus maximus). In a surprising revelation, researchers have determined that basking sharks, similar to great white sharks, mako sharks, and tuna, are regional endotherms, meaning they can keep their core body temperature warmer than the surrounding water. Credit: Greg Skomal / NOAA Fisheries Service
Basking sharks, known for their harmless, plankton-consuming habits, have been unexpectedly found to be regional endotherms, keeping their body temperature higher than the water in which they live, a characteristic usually linked with high-speed swimming apex predators.
Nearly 99.9% of fish and shark species are ectothermic, with their body tissues typically matching the temperature of the water they swim in. However, researchers have now identified the basking shark as a rare exception.
These sharks manage to keep their core body warmer than the surrounding water, a trait also observed in top sea predators like great white sharks, mako sharks, and tuna.
Comparisons Between Predatory and Plankton-Feeding Marine Species
The aforementioned examples are known as “regional endotherms” and are high-speed swimmers and apex predators at the top of the food chain. Scientists have speculated that their ability to maintain warmth aids in their predatory lifestyle, with evolution shaping their physiology to suit their needs.
Nonetheless, an international team of researchers led by those from Trinity College Dublin, has proven that the docile, plankton-eating basking sharks also exhibit the traits of regional endotherms, despite having lifestyles very different from white sharks and tunas.
This unexpected finding raises various conservation, ecological, and evolutionary issues.
Unraveling the Secrets of Basking Sharks
Haley Dolton, a PhD candidate at Trinity’s School of Natural Sciences and the lead author of the study published in the international journal, Endangered Species Research, stated:
“The basking shark stands as a testament to our limited knowledge about shark species in general. The fact that we still have so much to learn about the world’s second largest fish, a recognizably huge and charismatic creature, underscores the challenges researchers face in obtaining information necessary for effective conservation strategies.”
Although basking sharks were granted legal protection in Irish waters only last year, they have witnessed a significant drop in population in the NE Atlantic over the past century and continue to face numerous future challenges.
Potential Impact of the Recent Discovery
Dolton added, “Regional endotherms are believed to utilize more energy and may react differently to ocean warming compared to other fish species. As a result, further research is required to determine how these new findings might alter existing assumptions about their metabolism or potential distribution changes during our climate crisis, an area of focus for marine biologists as our planet and its oceans continue to warm.
“Hopefully, this kind of research will maintain the momentum required for the effective protection of these amazing creatures in Irish waters and beyond.”
Research Methods and Results
To make this discovery, the research team (which included scientists from the University of Pretoria, Marine Biological Association, Queen’s University Belfast, Zoological Society of London, University of Southampton, and Manx Basking Shark Watch) dissected dead basking sharks that had washed up on the shores of Ireland and the UK.
They discovered that basking sharks have cruise-swimming muscles deep within their bodies, similar to white sharks and tunas, while most fish have this “red” muscle nearer to their external surface.
They also found out that basking sharks have robust muscular hearts that possibly contribute to high blood pressures and flows. While most fish species have comparatively “spongy” hearts, basking shark hearts resemble those of other regional endotherm species.
Subsequently, the team developed a new low-impact tagging method to record the body temperature of free-swimming basking sharks off the coast of Co Cork, Ireland. They managed to get close enough to the 26 feet long basking sharks to safely attach the tags, which recorded muscle temperature just below the skin for up to 12 hours before they automatically detached and were retrieved by the researchers.
These tags showed that the muscle temperature of basking sharks consistently remained higher than the water temperature, almost exactly matching their regionally-endothermic predatory counterparts.
Reassessing Assumptions About Marine Species
Nicholas Payne, Assistant Professor in Trinity’s School of Natural Sciences and senior author of the study, stated:
“The findings bring an intriguing new perspective to our understanding of form versus function in fishes. Until now, we assumed that regional endothermy was a trait found only in apex predatory species occupying high positions in the marine food chain.
“Having found a species that feeds on minuscule plankton and yet shares these rather unique regional endotherm features, we might need to revise our assumptions about the benefits of such physiological adaptations for these animals.
“It’s like suddenly discovering that cows can fly.”
Reference: “Regionally endothermic traits in planktivorous basking sharks Cetorhinus maximus” by Haley R. Dolton, Andrew L. Jackson, Robert Deaville, Jackie Hall, Graham Hall, Gavin McManus, Matthew W. Perkins, Rebecca A. Rolfe, Edward P. Snelling, Jonathan D. R. Houghton, David W. Sims and Nicholas L. Payne, 20 July 2023, Endangered Species Research.
DOI: 10.3354/esr01257
Haley Dolton’s research is funded by the Irish Research Council, with support from the Fisheries Society of the British Isles. Dr. Nicholas Payne’s funding comes from Science Foundation Ireland.
Table of Contents
Frequently Asked Questions (FAQs) about Basking Sharks
What is the major discovery about basking sharks?
The major discovery is that basking sharks are regional endotherms, meaning they maintain a higher core body temperature than the water they inhabit, a trait typically found in fast-swimming apex predators.
What are the implications of this discovery?
The findings raise a range of ecological, evolutionary, and conservation issues. The unique warm-blooded trait of basking sharks may impact their metabolism and response to ocean warming differently than other species, necessitating further research and potential adjustments to their conservation strategies.
Who were the lead researchers in this study?
The study was led by Haley Dolton, a PhD candidate at Trinity’s School of Natural Sciences, and Nicholas Payne, an Assistant Professor in Trinity’s School of Natural Sciences.
How was the research conducted?
To make the discovery, the research team dissected dead basking sharks that had washed up on the shores of Ireland and the UK. They also designed a new low-impact tagging method to record the body temperature of free-swimming basking sharks off the coast of Co Cork, Ireland.
What makes basking sharks unique among other species?
Basking sharks are unique because, despite being gentle, plankton-feeding creatures, they share a regional endotherm trait with high-speed swimming apex predators. This means they can maintain a higher core body temperature than the surrounding water.
What other marine species are known to be regional endotherms?
Apart from basking sharks, other known regional endotherms include great white sharks, mako sharks, and tuna. These species are typically high-speed swimmers and apex predators at the top of the food chain.
More about Basking Sharks
- Basking Shark – Wikipedia
- Endotherm – Wikipedia
- Regional Endothermy – Encyclopedia of Life
- Endangered Species Research Journal
- Trinity College Dublin – School of Natural Sciences
- Irish Research Council
