Once again, the great white sharks are back in the waters surrounding Cape Cod chasing prey. The ocean is their domain and we are just intruders who from time to time end up as either an hors d’oeuvre or full meal for him.

I had the opportunity to study sharks up close and personal when I worked as an assistant aboard the research vessel Delaware in the summer of 1965. On the Grand Banks, any sharks we caught by long line, we had to lean over the side and tag them just below the first dorsal fin.

The existence of sharks dates to the Devonian period, which spanned the time between 265 to 320 million years ago. From fossils found in Devonian beds of limestone in Ohio, paleontologists have discovered teeth and body outlines of sharks that resemble the modern-day creature. No skeletons were ever found since sharks are made of cartilage and dentine, which just leaves an outline of these creatures in the rocks. Archaeologists, digging in a fossil bed in Georgia a few decades ago, discovered a shark’s tooth, triangular in shape, which measured 3-and-a-half inches from the base to its apex. Based on the size of this tooth, scientists estimated this shark would have measured 65 feet in length and with its mouth fully opened, would have measured 5 feet from the upper to lower jaw.

Roots of the word shark seemed to have evolved from schurke, the German word for villain or from the Angelo-Saxon word sceran, which means to shear or to cut. Shark is a fine word though. Its very sound is sharp. Perhaps no other cry can command such immediate attention. It is a word whose very letters are rooted in fear, the fear of a mouth filled with biting, slashing teeth.

Scientists estimate that there are between 250 and 350 species of sharks in existence today. Sharks are still as strong and healthy and in as large numbers today as they were when the tyrannosaurus rex reigned supreme over the land.

Sharks’ bodies are streamlined for smooth movement. Their pectoral fins, located just behind their gills, prevent them from sinking to the bottom of the ocean where they will drown. They also help to stabilize them, preventing them from rolling over. Because sharks have no swim bladder like bony fish do, they must always keep swimming. The caudal fin however, the tail of sharks, is the source of thrust as they move from side to side.

Concerning how fast sharks can swim, Thomas Helms, a researcher in the Florida Keys, once pulled along side of a mako shark. As it began to accelerate, Helms clocked it at 30 miles per hour, or 27 knots, before it sounded. He clocked other species such as the great white at speeds between 10 to 15 miles per hour.

Sharks’ mouths are a highly effective physiological adaption perfectly suited to do their job. There are two elements that make their mouths so effective: their teeth and their jaws. Their teeth are very sharp and serrated, facing inward. So whatever prey these creatures bite into, will not easily escape from their mouths unless they decide to release it. Sharks do not chew their food but use their teeth to grab, hold and rip their prey into bite-size chunks.

Sharks’ teeth are in five rows, lying one on top of the other like pages of an open book. When they lose a tooth, it is replaced by another one in a 24-hour period. As for their jaws, they are very powerful when they bite. Dr. Perry W. Gilbert of the Lerner Marine Laboratory, located on the island of North Bimini in the Bahamas, developed a bite meter made from an aluminum cylinder of a known hardness, enclosed by four quadrants of steel containing 12 stainless-steel ball bearings. It was wrapped in bait and lowered into a pen holding an 8-foot dusky shark, which clamped down on it right away. After examining the dent in the meter, Gilbert calculated the shark’s biting pressure at approximately 18 tons per square inch.

Sharks have no problem locating prey since they have a very keen sense of smell that allows them to track blood hundreds of yards away.

Sharks have the unique makeup, a way by which they can detoxify cancerous producing agents in their bodies. The digestive juices in sharks’ stomachs are made up of hydrochloric acid and an enzyme known as pepsin that helps them to digest bone, wood, rubber, paper and even metal. When this collection of indigestible junk grows large enough to become a burden, sharks simply belch up the whole works and swim off in search of more food.

Basically, sharks will attack for two reasons, curiosity and hunger. But no matter how you look at sharks, they are tough and durable and when viewed in their own underwater kingdom, they seem as though they can swim on forever.

Rick Gonsalves is a resident of Essex. 

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