Giant hammerhead sharks are masters of the “thermal hustle,” maintaining peak hunting performance over a surprisingly wide range of ocean temperatures, a study in the Journal of Experimental Biology reveals.
As the climate crisis unfolds, the findings provide insight into the species’ possible future movements and survival.
All living things have an optimal range of temperatures they can live in. Some thrive when the mercury falls, whilst others embrace the scorching heat. When they are pushed outside their preferred range, many species experience a sharp decline in performance.
Not so, the great hammerhead shark. Their performance drops a little, but not so much. “This tells us that great hammerheads might tolerate changing climates better than other species,” says Yannis Papastamatiou from Florida International University.
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The great hammerhead shark is the largest species of hammerhead shark, growing up to 6m long or more. This critically endangered species is found in tropical and warm temperature waters worldwide, where it typically inhabits coastal areas.
To study how well the great hammerheads perform, Papastamatiou and colleagues used advanced biologging technology to track the movement, acceleration, depth and water temperature of nine hammerheads in the waters off Florida and the Bahamas. Then they used this information to create a “thermal performance curve”, which shows how the sharks’ performance changes across a range of temperatures.
The sharks performed best at a sweet spot of 29.3°C, but either side of this their performance dropped less steeply than was expected. This means they can effectively hunt fast-moving prey like blacktip sharks in winter and fast-moving tarpon and barracuda in summer.
The finding suggests that the sharks can perform well across a relatively broad range of temperatures, yet for the most part, they tended stay in their comfort zone. Reviewing historical shark catch data and satellite tag records, the team also found that great hammerheads were most often found in temperatures close to their preferred 29.3°C.
Great hammerhead sharks have experienced drastic population declines in the past several decades. “As ocean temperatures change, hammerheads may shift their range to stay within the temperatures where they perform best,” says Papastamatiou. “That could bring them into areas with heavier fishing pressure.”
Thermal performance curves can be used to help predict the future movement of species, but other factors, such as the availability of food and presence of human activity, can also have an effect. The new research highlights the importance of these additional factors.
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