Tuesday, June 24, 2014

Great White Sharks

Here is a great white shark.  It and its fellows swim the seven seas, moving from one feeding opportunity to the next.  Individual sharks have been know to travel from the shores of one continent to another.

The great white shark is a dedicated and exclusive carnivore, feasting on seals, dolphins, smaller sharks, fish and rays.  It has rows of teeth, sometimes as many as 300 teeth, to assist in its pursuit of prey.

(Great whites that ate humans were features in a book, Moby Dick, and a movie, Jaws, but experts claim that sharks are mostly curious about, but not hungry for, people.  Sharks are more likely just to move in and take a taste, say an arm or foot, according to scientists and Australian surfers.  This all may be true, but if I saw a shark fin in the water, I'm pretty sure I'd swim to shore in a hurry.)

An organization called OCEARCH has been studying the movements of great white white sharks for several years now.  It does this by capturing sharks and affixing transmitters to their dorsal fins.  When the sharks surface, the transmitters emit signals.

This may sound uncomfortable for the shark, or like an invasion of privacy.  But it is a much lesser indignity than being fished.  While shark fin soup remains a delicacy in some parts of the world, the harvest of sharks is increasingly being regulated or banned.

Pick a shark, any shark

So far, OCEARCH is tracking 47 great whites, all of which can be followed by name searches on the organization's website. (Albert, Beamer, Marcella, Princess, etc.)

The movements of two East Coast-based sharks have been much in the public eye these days.

One is Mary Lee, a 3,500-pounder, who was briefly detained and tagged off Cape Cod last September.  Later in the year, she swam close to several Florida beaches before moving north and attracting great interest in Northeast states.

Since then, Mary Lee has swung back south.  Here is her recent course, as tracked by OCEARCH pings.

Meanwhile, Floridians were following the movements of Katharine, a more svelte, single-ton creature, also tagged off Cape Cod last year.  In May, Katharine took the route below around the Florida Coast.  She now is in the Caribbean and thought to be headed toward Texas shores.

Katharine and Mary Lee have become so popular that they can be traced by Google searches, i.e, Where is Katharine the shark?  Mary Lee even has her own facebook page.

Not much is known about the habits of great whites.  They are believed to mate out at sea, and the gestation period of baby sharks is estimated at 18 to 24 months.

Until a University of Tasmania study a year or two back, their diets were underestimated by two thirds.  It takes a lot of seals to fuel a great white.

The leader of the study, Jayson Semmens, told Discovery News, "We don't have a good handle on the population sizes of white sharks.  We know that sharks in general are under pressure around the world from overfishing."

"They're quite vulnerable," he added, "because of their life history. They're long-lived, they reproduce late in their life and they produce a small number of offspring."

In fact, the number of great white sharks in the Atlantic Ocean, which had declined in the 1960s to the 1980s, seems to be increasing rapidly.  Scientists take this as a good sign because great whites are natural regulators of other ocean species.

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