I had been underwater now for about two hours and the cold was setting in. I was being towed behind a small boat 150 km from shore and counting reef fish as part of my underwater surveys on the Great Barrier Reef. On one side of me the water was about 10 metres deep, bright and colorful with coral and fish and then it plunged down to nearly 1000 metres of icy darkness just beneath me.
I’d had company since I first dived into the inky water. Just on the edge of my visibility a pair of Oceanic Whitetip Sharks, Carcharhinus longimanus, had followed my every move. Famed oceanographer, Jacques Cousteau described them as "the most dangerous of all sharks" and his words echoed in my mind.
All I could see of them was the silvery tips of their huge pectoral fins. Growing to four metres and 170 kg and considered to be responsible for most open ocean shark attacks, these elegant fish are nature’s ultimate predator and were my biggest worry.
A young Oceanic Whitetip shark shows off its huge pectoral fin.
That was 30 years ago and Oceanic Whitetips were always around me. The last time I dived the outer Barrier I was alone. In 1969, Lineaweaver and Backus wrote of the Oceanic Whitetip: "[it is] extraordinarily abundant, perhaps the most abundant large animal, large being over 100 pounds [45 kg], on the face of the earth". Now overfishing has brought about a catastrophic collapse in their numbers. The International Union for the Conservation of Nature lists them as “Critically Endangered” in the Northwest and Central Atlantic and “Vulnerable” globally.
"Overfishing of sharks is now recognized as a major global conservation concern, with increasing numbers of shark species added to the International Union for the Conservation of Nature's list of threatened species," they say in the latest issue of the science journal PLos ONE.
Shark meat is low priced so fishermen try to fill their boats with only the valuable fins. Contrary to a UN Resolution to ban the practice, the fins are usually sliced off the shark while it is still alive. The cheaper body is thrown back into the ocean and the shark, unable to swim, dies slowly. Shark fin purchases are increasing at the rate of five percent per year in mainland China. Globally, catches have more than tripled in the last 50 years even though sharks are becoming harder to catch as their numbers fall.
Dr. Shelley Clarke’s estimate of sharks harvested for their valuable fins is between 26 million and as many as 73 million sharks each year worldwide. Her best estimate is 38 million sharks killed annually. This number is an astonishing three to four times higher than is reported by world markets to the United Nations (FAO).
Their findings, published February 20, 2013 in the journal PLoS ONE, show that some of these sharks roamed nearly 2,000 kilometers from the spot where they were caught, but all individuals returned to The Bahamas within a few months.