Friday May 12, 2023


Because it makes them better hunters, scalloped hammerhead sharks (Sphyrna lewini) have evolved a unique method to avoid losing body heat when they dive for prey in deep, cold waters: they close their gills.

Numerous fish and marine-mammal species are known to dive from the warm surface to deeper waters to hunt. However, ectothermic, or ‘cold-blooded’, animals face the challenge of how to conserve their body temperature to keep their metabolism active enough for hunting when the surrounding water can be just a few degrees above freezing.

“The most rapid point of heat loss for any fish, even a high-performance fish, is always at the gills,” says Mark Royer, a postdoctoral researcher in shark physiology and behaviour at the Hawaiʻi Institute of Marine Biology in Kaneohe, part of the University of Hawaiʻi. Because of the high volume of warm blood flowing through the gills, they are “essentially just giant radiators strapped to your head”, he says.

Some fish, such as the whale shark (Rhincodon typus), are able to conserve their body heat when diving through sheer size. Others, such as tuna, marlin and the family that includes great white (Carcharodon carcharias) and mako sharks (Isurus oxyrinchus), have evolved specialized heat-exchange systems at the gills that avoid too much body heat being lost.

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