Cats, condoms and licence plates: The sharks that will eat anything
You get boulders flying, the seabed all stirred up. You see sharks, manatees… thrown onto the beach – Neil Hammerschlag
Tiger sharks are ectothermic, or cold-blooded, says Hammerschlag, meaning they can't create their own heat. Their movements, therefore, tend to follow a layer of water, called an isotherm, at 26C (78.8F) – the same temperature at which a tropical cyclone can begin to form.
When pregnant, some tiger sharks even take refuge in the balmy waters of Tiger Beach – relying on the environment around them to "warm the bun in the oven", says Hammershlag.
Hammerschlag and his team had previously attached acoustic tags to the Tiger Beach tiger sharks to study the impact of tourism on the animals. The tags keep transmitting for 10 years so, in 2016, Hammerschlag saw an opportunity to study the sharks' reaction to Hurricane Matthew.
"My prevailing thought was that they would all flee," says Hammerschlag. "In shallow water, you get boulders flying, the seabed all stirred up. You see sharks, manatees…thrown onto the beach. But deeper water is not disturbed. Deep water provides a refuge from the storm."
William TanPrevious studies back up this assumption, showing that many sharks tend to leave coastal areas when a storm is imminent, and some species leave more than a week before one arrives.
Yet when Hammerschlag and his team tracked the tiger sharks before, during and after the hurricane, "I was shocked", he says. "Not only did they not flee, but on the very same day more tiger sharks arrived.
"The storm killed a lot of things: turtles, fish, lobsters, crabs, birds. We think the tiger sharks saw the coming storm as a scavenging opportunity to feed on the dead and dying."
Hammerschlag believes the tiger sharks were able to remain in the area during the storm because, he says, "they are built like tanks".
Tiger sharks have also learnt to take advantage of seasonal events, when they know there will be an abundance of food.
Take green turtle breeding season at Raine Island, Australia, for instance, or the summer fledging of albatross chicks at French Frigate Shoals atoll, Hawaii. The sharks time their arrival to coincide with a glut of easy prey – sometimes turning up at the same spot on the same day in consecutive years.
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