Saving the ‘perfect predator’ – Rookery Bay talk explains why sharks need protection

“How fast can sharks swim?” Dr. Jose Castro was asked, during the Q&A after his lecture on sharks at the Rookery Bay Environmental Learning Center on Wednesday evening.

“Faster than you can,” he replied, and went on to say that with all the research on sharks, he doesn’t really have a good definitive answer to the question. Castro just published “The Sharks of North America,” which many are calling the definitive word on shark biology and behavior, and admitted to trying to catch sharks when swimming underwater, so if anyone knew, it would likely be him.

But measuring speed of short bursts of sub-aquatic speed presents severe challenges, said Castro, although he did say when they close in on their prey, “they move at the speed of thought,” and estimated they reach 20 to 30 mph.

Castro, who titled his talk “The Perfect Predator,” clearly admires the species he has studied for decades. Wednesday’s lecture was part of Rookery Bay’s “Summer of Sharks,” with a variety of shark-related events and activities for adults and children. Refreshments including beer and wine were included in the admission charge of $10 ($5 for Friends of Rookery Bay).

Sharks are one of the oldest species, stretching back over 450 million years, said Castro. All human evolution, by comparison, has taken place in one hundredth of the time, just 4.5 million years.

Since sharks are cartilaginous, with their skeletons make of cartilage similar to human noses, only their teeth are likely to be preserved as fossils, making it difficult to be certain about prehistoric starks. Castro showed a photo of a fossilized shark’s tooth that dwarfed the hand that held it.

Today, the whale shark, up to 40 ft. long, is the largest fish in the world, while other sharks measure only inches when full-grown, he said. With hundreds of individual species, sharks are incredibly diverse. Most are cold blooded, but some including the mako shark are warm blooded. Some lay eggs, some give birth to live pups.

Most sharks live only in salt water, but some including the bull shark, which has attacked and killed humans, swim in fresh water as well.

Human attacks are rare, though, as different shark species specialize in particular prey, and have evolved to be that perfect predator. Their teeth, said Castro, illustrating his talk with projected slides, cut precisely. One variety, the cookie cutter shark, should actually be called the melon baller, for the round scoops it takes out of larger fish, he said.

Sharks can sense prey from miles away, with their famous ability to smell blood in the water. Close up, they have electro-receptors to enable them to locate prey too close for them to see clearly, as a great white’s head may by two feet across. Even their scales, appearing as fascinating mosaics of variegated bat shapes when magnified, are specialized to allow them to slip through the water silently.

While spearfishing underwater puts humans in greater danger, said Castro, most shark/human predation has sharks on the losing end. “Man eating shark” generally takes place at the table, not in the water. Many shark species have been put under incredible pressure in the last two decades, said Castro, due to overfishing, particularly for the Asian market and the popularity of shark fin soup. The lengthy, two-year gestation period of sharks makes them vulnerable, as it takes a long time for the population to rebound.

But fear of sharks is out of all proportion to their actual number of attacks on humans.

“My house is undergoing a ‘jaws-o-phobia’ moment,” said Patty Meyers during the Q&A, due to a report of a hammerhead being spotted locally. Castro replied that sharks are way down the list of dangers to people, below “mass murderers and vampires,” but added this area has lots of hammerhead sharks.

“This is the best place to see hammerheads,” he said.

Heyward Boyce of Marco Island cut to the chase with his question.

“What difference does it make if we eat all the sharks?” he asked.

“Everything has its place in nature,” replied Castro. “We want to leave the environment in the same shape, to ensure we live ourselves. If the top predator is okay, the ecosystem is okay.”

And the only competition the shark has for the top predator spot is man.

Rookery Bay’s Summer of Sharks continues July 27 with shark expert and scuba diving pioneer Stan Waterman.

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