SCUBA Juy/August 2023 issue 137 | Page 49

Personality goes a long way Do sharks have individual personalities ? Paul Cox reviews the science , finding some compelling evidence in favour of the notion

Hammerheads are ‘ freedivers ’

Scalloped hammerhead sharks have evolved a unique method to avoid losing body heat , a new research paper argues . In previously unobserved behaviour , scientists now believe the sharks “ hold their breath ” simply by closing their gill-slits at critical moments . Numerous fish and marinemammal 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 highperformance fish , is always at the gills ,” says Mark Royer , a postdoctoral researcher in shark physiology at the University of Hawaii . Because of the high volume of warm blood flowing through the gills , they serve as “ giant radiators strapped to your head ”, Royer says . But the parallels between animals that breathe using lungs and gills are no coincidence , the research team says , after concluding that tropical scalloped hammerhead sharks effectively freedive .

meant to go around a door . The architrave measured up to six metres , or nearly 20 feet . The discoverer , Gideon Harris , was swimming at a popular spot about 24 miles from Tel Aviv . Harris contacted the Israel Antiquities Authority , who said they had been aware of the cargo for some time , but had lost the precise location . Koby Sharvit , director of the authority ’ s underwater archaeology unit , said : “ The recent storms must have exposed the cargo , and thanks to Gideon ’ s important report we have been able to register its location and carry out preliminary archaeological investigations .”

Many years ago , I worked in an aquarium . I spent most of my days standing with visitors looking into tanks and talking about the animals . And of course , these conversations often involved the sharks . Through those thousands of conversations , I learnt an awful lot about how people view sharks , what perceptions they arrived with and what they took away .

When you look into a shark ’ s eyes , you don ’ t get a lot back . Aquarium visitors often commented on the “ cold ” and “ malevolent ” look that they received from the animals . The implication that sharks are unthinking and single-minded plays into the stereotypes that we regularly encounter and that idea that all sharks are the same . We know the animals that we have around us and we credit them with all sorts of character traits . Talk to any dog owner and they ’ ll wax lyrical about all their little quirks and their individuality . Dogs have personalities . But sharks don ’ t . Or do they ?

As divers , we ’ re more aware than most that different sharks behave differently . This is personality . Scientists have been studying animal personality for years . But usually , it ’ s done with smaller animals that can be studied in a captive environment . It ’ s not so easy with free-swimming sharks .

I recently came across a fascinating body of work that ’ s been carried out over the last ten years or so at the research station in

Lemon sharks in the Bahamas

Bimini , Bahamas . Moving from semi-captive studies to working with wild sharks , the main focus has been assessing sociability and the tendency to explore . The theory in test is called the “ pace of life hypothesis ”. This simple piece of logic suggests that animals make choices between being more adventurous – increasing the risk of predation but also increasing the potential for richer feeding grounds leading to faster growth – or adopting a more cautious strategy . It ’ s a choice that we all face in one way or another at some stage .

Why does it matter ? Because success is a mixture of physical traits and behaviour . In a changing environment , behaviour is the more flexible of the two and therefore will have a large bearing on outcomes . What the researchers found was that the sharks did conform to the pace of life hypothesis . Sometimes . But they also adapted their behaviour when there was more competition , when predation risk increased or when there were a lot of newborns in the population .

The work continues , as scientists dig deeper into how personalities express behaviours in the shorter term . But the message is clear . Sharks have a lot more going on than their eyes tell us . They ’ re not all the same and , just like all of us , they ’ re continually making decisions to get the best out of their lives .

www . sharktrust . org

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