Oceanic Whitetip Sharks and Overfishing Apex Predators

     Dr. Gerry Goeden

I was recently bemoaning the sorry state of the Oceanic Whitetip Shark and mentioned that there was just a Conference of the Parties (CITES) meeting in Bangkok earlier in March to look at their protection. What was only a few years ago the most abundant large predator on Earth is now little more than a memory thanks to overfishing and shark finning.

 An Oceanic Whitetip Shark and accompanying pilot fish

I also made mention of the fine work of Dr. Shelley Clarke who estimated from market surveys that between 26 million and as many as 73 million sharks were harvested each year worldwide. Her best estimate was 38 million sharks killed annually.

We may have had that wrong. On March 1, 2013, "Global Catches, Exploitation Rates and Rebuilding Options for Sharks," was published by Dr. Worm and three other researchers from Dalhousie University teamed up with scientists from the University of Windsor in Canada, as well as Stony Brook University in New York, Florida International University (FIU) in Miami and the University of Miami. A very powerful team indeed.

Their shocking findings are that shark fishing is now globally unsustainable. Their more recent estimates put the carnage at 97 million in 2010. The possible range of mortality is between 63 and 273 million annually. This equates to somewhere between 7,200 and 31,000 sharks per hour.

Carcharhinus melanopterus on a Guam reef

"Sharks are similar to whales, and humans, in that they mature late in life and have few offspring” said Boris Worm. “Our analysis shows that about one in 15 sharks gets killed by fisheries every year. With an increasing demand for their fins, sharks are more vulnerable today than ever before."

Why am I so upset? It was never fun swimming around in a 1000 m of water with things described by Jacques Cousteau as "the most dangerous of all sharks". Why should I care if they are gone?

The research I was doing at that time looked at the make up of the marine fish community as it was exposed to fishing pressure. Specifically, to fishing aimed at top predators on the coral reef. I was trying to find out how much fishermen were reducing the stocks of valuable food fish on the Great Barrier Reef. I found that stocks were devastated by up to 95% in some places.

But I discovered something that wasn’t known before. I came up with a mathematical expression that predicted changes in the entire fish community. I published the work in 1982.

That’s right! Not just the species the fishermen were catching; it looked like everything changed and more importantly, it looked like it might never change back. Sadly, this idea didn’t catch on and was buried in scientific libraries. Everyone believed that if you left things alone for a while they would repair themselves and go back to the way they were in the “good old days”. This comes from the idea of ‘renewable resources’ and is the way we see the world around us.

Hammerhead sharks are seriously endangered and facing extinction

The years past and things started to go very wrong in the Caribbean. Reefs there were being over-run by seaweed, fish were gone, and corals were dying. From about 2000 researchers were looking at a variety of possible causes. By March, 2009 researchers had found that fish abundance that had been stable for decades had given way to significant declines from 1995. 

By June, 2012 Dr. Roff had completed a study raising concerns about the future of Caribbean coral reefs. Seaweeds were blooming so fast that corals were unlikely to recover in the absence of enough seaweed eating fish.

Now in March, 2013; "This is a big concern because the loss of sharks can affect the wider ecosystem," said Mike Heithaus, executive director of FIU's School of Environment, Arts and Society. "In working with tiger sharks, we've seen that if we don't have enough of these predators around, it causes cascading changes in the ecosystem, that trickle all the way down to marine plants." Such changes can harm other species, and may negatively affect commercial fisheries, Heithaus explains.

Science has been nailing the problem down to over exploitation of the apex predators – sharks and some groupers. It was during the last two years that this research caused my early work to be dusted off and looked at again. My 1982 concept is now becoming a cornerstone of contemporary thinking in coral reef management.

Put simply, we must have all the species in reasonable numbers if we are to maintain healthy and sustainable fisheries. Eliminating an apex predator is like pulling a couple of ‘chips’ out of your computer. It still runs but it doesn’t run the way you want it to.

In my earlier work I forecast that “the concept of renewable resources may not be broadly applicable to the coral reef and the relationship between (apex) species abundance and (change) – may be less a management tool than a picture of the demise of the reef fish community as we know it”.

A juvenile Oceanic Whitetip Shark

Fancy words? Not really. Where nature is concerned we just have to understand that most of the time we don’t understand. We can’t go into an ecological system that evolved hundreds of millions of years before man set foot on the planet and think we can exploit it however we wish and that it will simply cope with our being there.

If we can learn anything from natural history it is that when systems begin to collapse there is a point from which there may be no turning back. If you doubt this then ask the dinosaurs for their opinion.

(This is the second in this series. For more information on sharks please visit my earlier post.)


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Oceanic Whitetip Sharks Endangered Through Finning

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.

Oceanic Whitetips are often accompanied by pilot fish.

 

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.

 

But the Oceanic Whitetips are not alone in this tragedy. "There is mounting evidence of widespread and ongoing declines in the abundance of shark populations worldwide, coincident with marked rises in global shark catches in the last half-century," say Mizue Hisano, Professor Sean Connolly and Dr William Robbins from the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

 

Tiger Sharks are heavy bodied but capable of bursts of speed that don't fit their usually sluggish behavior.

"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.

Interest is growing worldwide in protecting these sharks. Now more species have been added to  Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This happened during the Conference of Parties meeting in Bangkok, Thailand, March 3-14 of this year. Sadly, the nations of the world were voting on the restriction of international trade only in endangered sharks. This may not be enough as the fishery will quickly shift to other less desirable species to meet its growing demands.

 

Oceanic Whitetips were once the most common large predator on the planet but fishing is now pushing them toward extinction.

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.

 

A finned shark lies helpless on the bottom facing a slow death by starvation. Outlawed as cruelty by many countries there is no enforcement.

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).

Scientists from the International Union for the Conservation of Nature (IUCN) are shocked to find that more than half of many large shark species have virtually disappeared in the last 30 years. The collapse in shark numbers is due to the unprecedented demand for shark fins. Each hour about 5000 sharks have their fins sliced off and their bodies thrown into the sea. At current rates of decline, there will be no shark fins and unfortunately very few sharks by 2030.

Will the CITES Conference in Bangkok be able to protect the Oceanic Whitetip? I’m not so sure.

A research team, which included researchers from Microwave Telemetry, Inc., the Cape Eleuthera Institute, and the Institute for Ocean Conservation Science at Stony Brook University, attached satellite tags to mature oceanic Whitetip sharks in The Bahamas. The tags recorded depth, temperature, and location for pre-programmed periods of time. At the end of the time period the tags self-detached from the sharks and reported their data to orbiting satellites.

 

Reef sharks cruise the reef slope in Great Barrier Reef waters  No species are safe from overfishing.

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.

Protecting endangered Whitetips in signatory countries will have little effect if they travel into unprotected seas. Of the eight tagged Oceanic Whitetip sharks tracked for more than a month, three stayed within the Bahamas Exclusive Economic Zone (EEZ). The other five sharks made long-distance movements outside of the EEZ with one traveling as far as Bermuda.

So why are shark fins attracting such attention?

Shark fin soup is a delicacy served at Chinese weddings and other celebrations for centuries (since Ming Dynasty). Recently this expensive product has become part of business dinners in Southeast Asia. Because the fins are the most expensive part of the shark, having them on the menu is a sign of prosperity.

Oceanic Whitetips belong to an ancient group of fish and produce from one to 15 pups after a year’s gestation. They are unable to produce enough pups to balance the high fishing rates and so the number of sharks gets smaller each year. But the Oceanic Whitetip is at the top of the food chain and its abundance regulates the ecological relationships of all the marine life in the complex web of predator and prey beneath them.

Within 30 years shark fin soup will no longer symbolize prosperity. Instead it will be a tribute to man’s greed and lack of commitment to his own future.

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