Overfishing sharks may destroy ecosystem!
Fewer big sharks in the oceans mean that bay scallops and other shellfish may be harder to find at the market, according to an article in the March 30 issue of the journal Science, tying two unlikely links in the food web to the same fate.
A team of Canadian and American ecologists, led by world-renowned fisheries biologist Ransom Myers at Dalhousie University, has found that overfishing the largest predatory sharks, such as the bull, great white, dusky, and hammerhead sharks, along the Atlantic Coast of the United States has led to an explosion of their ray, skate, and small shark prey species.
"With fewer sharks around, the species they prey upon – like cownose rays – have increased in numbers, and in turn, hordes of cownose rays dining on bay scallops, have wiped the scallops out," says co-author Julia Baum of Dalhousie.
"This ecological event is having a large impact on local communities that depend so much on healthy fisheries," says Charles Peterson, a professor of marine sciences biology and ecology at the Institute of Marine Sciences, University of North Carolina at Chapel Hill and co-leader of the study.
The research builds upon an earlier study by Myers and Baum, published in Science in 2003, which used data from commercial fisheries to show rapid declines in the great sharks of the northwest Atlantic since the mid-1980s. Now, by examining a dozen different research surveys from 1970-2005 along the eastern U.S. coast, the research team has found that their original study underestimated the extent of the declines: scalloped hammerhead and tiger sharks may have declined by more than 97 percent; bull, dusky, and smooth hammerhead sharks by more than 99 percent.
"Large sharks have been functionally eliminated from the east coast of the U.S., meaning that they can no longer perform their ecosystem role as top predators," says Baum. "The extent of the declines shouldn't be a surprise considering how heavily large sharks have been fished in recent decades to meet the growing worldwide demand for shark fins and meat."
Sharks are targeted in numerous fisheries, and they also are snagged as bycatch in fisheries targeting tunas and swordfish in both U.S. and high seas fisheries. As many as 73 million sharks are killed worldwide each year for the finning trade, and the number is escalating rapidly.
Ecologists have long predicted that the demise of top predators could trigger destructive consequences. Researching such effects, however, has been a challenge.
"This is the first published field experiment to demonstrate that the loss of sharks is cascading through ocean ecosystems and inflicting collateral damage on food fisheries such as scallops," says Ellen Pikitch, a professor at the University of Miami Rosenstiel School of Marine and Atmospheric Science and executive director of the Pew Institute for Ocean Science. "These unforeseen and devastating impacts underscore the need to take a more holistic ecosystem-based approach to fisheries management."
As great shark populations plummeted, their elasmobranch prey—rays, skates, and smaller sharks—increased considerably, according to research surveys looking at the past 16 to 35 years. Cownose rays are most conspicuous among the 12 species showing increases because of their near-shore migrations. With an average population increase of about eight percent per year, the east coast cownose ray population may now number as many as 40 million. The rays, which can grow to be more than four feet across, eat large quantities of bivalves, including bay scallops, oysters, soft-shell and hard clams, in the bays and estuaries they frequent during summer and migrate through during fall and spring.
In the early 1980s when Peterson sampled bay scallops in North Carolina sounds in late summer before and after the cownose rays passed through, he found that most scallops survived the ray predation, allowing the scallop population to support a fishery and still replenish itself each year. In contrast, sampling by Peterson and co-author Sean Powers in recent years—after the cownose ray population explosion—showed that the migrating rays consumed nearly all adult bay scallops in the area, except those protected inside fences that the researchers had put up to keep the rays out. By 2004, cownose rays had completely devastated the scallop population, terminating North Carolina's century-old bay scallop fishery.
"Increased predation by cownose rays also may inhibit recovery of oysters and clams from the effects of overexploitation, disease, habitat destruction, and pollution, which already have depressed these species," says Peterson, noting shellfish declines in areas occupied by cownose rays and examples of stable or growing shellfish populations in areas beyond the ray's northernmost limit.
Ecosystem effects of increases in the other ray, skate, and smaller shark species are unknown, but like the cownose ray, may also be cascading down to species lower in the food web.
"Despite the difficulty of piecing together ecosystem impacts of overfishing," co-author Travis Shepherd of Dalhousie emphasizes, "the real challenge will be to move beyond retrospective analyses and instead prevent ecosystem-wide changes from happening in the first place."
"Our study provides evidence that the loss of great sharks triggers changes that cascade throughout coastal food webs," says Baum. "Solutions include enhancing protection of great sharks by substantially reducing fishing pressure on all of these species and enforcing bans on shark finning both in national waters and on the high seas."
"Maintaining the populations of top predators is critical for sustaining healthy oceanic ecosystems," says Peterson. "Despite the vastness of the oceans, its organisms are interconnected, meaning that changes at one level have implications several steps removed. Through our work, the ocean is not so unfathomable, and we know better now why sharks matter."
Catching a great white shark will get you jail time!
There has been a shark-catching frenzy off the Chatham Islands ahead of a new law aimed at protecting one of the ocean's most feared predators.
From midnight Saturday, it is illegal to catch a great white shark in New Zealand waters.
Most people are terrified of them, but for great whites, the feeling is not mutual, as they have no fear of human beings.
Great white sharks are endangered in New Zealand waters, so much so that they are being afforded the same level of protection as the country's national bird.
Some Chatham Island locals have been in a frenzy over the last few days, trying desperately to catch as many sharks as they can before the new law kicks in.
But from midnight Saturday, instead of earning a payout, catching and killing a great white will cost you a jail term.
Increase in shark spotters will help protect both great white sharks and swimmers
A South African shark-spotting program to warn surfers and swimmers about the approach of great whites is to be expanded, environmentalists said Thursday, though they added the sharks have more to fear than humans.
Experts, who met Thursday to discuss how to balance protecting great white sharks and beachgoers ahead of the busy tourist season, stressed that people posed a far greater risk to sharks than the other way around. The great white was classified as a protected species in 2004 because of a rapid drop in numbers in waters around Australia and the Northwest Atlantic.
On average, there is just one shark attack on a human per year in Cape Town — and six in total in South Africa. But the great whites repeatedly hit the headlines because of close shaves, partly due to the increasing number of surfers and kayakers.
The number of great whites in South Africa is believed to have stabilized at around 1,200 since 1991, said shark expert Alison Kock, although she stressed the figures were unreliable because of the vast distances the sharks swim. Kock is in the middle of a drive to tag great whites in the waters around Cape Town to monitor their movements.
Trained spotters with binoculars and special glasses stand on hills above popular beaches. Each time a great white is seen entering the bay, a siren is sounded and the order given to clear the water.
Patrick Davids, 33, was among the original team of spotters recruited three years ago after shark attacks that killed an elderly woman and maimed a teenager.
"I used to sleep outside and scavenge through garbage bins. Now I‘ve got this job, life is great," he said.
The east coast resort of Durban has cut the number of fatalities from shark attacks to virtually zero by using nets — but at the price of killing some 600 tiger and bull sharks each year.
Under South African law, diving companies are only allowed to use bait to attract the sharks — not feed them — so the sharks do not associate boats with food. However, there are frequent reports that the law is being flouted by operators keen to ensure that the tourist‘s encounter with the shark is as spectacular and scary as possible.
"They are very curious and might just want to give a gentle nudge. But unfortunately for humans, that can cause serious injury," Cliff said.
The great white shark is threatened by extinction in the Mediterranean Sea
The great white shark is being hunted to extinction in the Mediterranean, while angel sharks have disappeared altogether from the North Sea according to a report from the UN's Food and Agriculture Organisation (FAO) meeting in Rome.
Although listed as an endangered species since 1983, the great white is legally protected only in Malta. The UK government promised to protect angel sharks in 2001 but, six years on, nothing has been done and they are now classified extinct.
World fisheries experts are seeking urgent protection measures and their study shows the crisis facing fish stocks of every sort all over the world.
The situation of the sharks is particularly grim. The reason is closely related to their well-known peculiarities - the fact they constantly roam the seas, have few offspring, and that their fins are a prized ingredient in a Chinese soup.
Sharks can live up to the age of 30, and many species only begin reproducing when they are aged six or more. The young remain inside the mother until they have hatched from the eggs. It means that when young females are caught in trawlers' driftnets - often as "bycatch" when the intended catch is sardines or anchovies - their whole lineages are wiped out.
"The number of offspring of a shark is very small," said Jorge Csirke, chief of Fisheries Management and Conservation at FAO, "and so if you kill a female you kill all her possible offspring. If you kill her early in her life, she hasn't reproduced at all." Sharks are especially vulnerable for other reasons, too, Mr Csirke explained. "They spend a lot of their lifespan in the high seas, outside the exclusive economic zones around countries, and in the high seas you don't have protection. No regional bodies are taking responsibility for them."
Another factor leading to their numbers falling - in quantities that are almost impossible to measure accurately - is the growing appetite for the cartilage that is the key ingredient in shark fin soup. To feed that lucrative market, many fishermen engage in what is known as "finning", stripping the fins from the shark then tossing them back in the sea to die of their wounds or be eaten alive. The practice has been declared illegal in several countries including Brazil, South Africa and the USA but it remains widespread and largely unmonitored.
"The fins fetch such a high price," says Mr Csirke, "if you go out with a small boat you don't want the whole fish on board, because what you can get for the fins is far more than you can get for the rest of the carcass."
According to FAO, finning causes the death of tens of millions of sharks every year, "directly threatening rare and vulnerable shark species and indirectly impacting other commercial species due to the effects of the removal of top predators from these food webs."
But despite the alarm over the rapid destruction of the world's sharks, governments even in Europe are slow to act. Angel sharks, abundant in coastal waters not long ago, have disappeared from the European seas and have been officially declared extinct in the North Sea by the International Council for the Exploration of the Sea.
The angel shark was nominated for strict legal protection in British waters in 2001. Six years on, the nomination is still in limbo and the angel shark still has no protection.
Shark sighting near Australian beach
Police and fisheries officers were notified of the "very large shark" swimming around the end of the jetty about 10.55am.
People flocked to the jetty after news of the sighting spread, with some witnesses claiming it was a great white.
Resident Ercole Lattanzio, who was at the jetty, said the shark was about 3m in length.
"It was a real bluey colour," Mr Lattanzio said.
"I clearly saw one shark, there may have been two, but one was swimming in a northerly direction and it went under the jetty and swam around in circles for about three to four minutes.
"I've never seen a shark that big, that close to shore before."
Witnesses said the shark had attacked crab nets that were dangled from the jetty.
While shark sightings are nothing new to metropolitan beaches, locals were concerned that the shark had been as close as 25m to the shore.
"That is concerning," Mr Lattanzio said.
"This is our local beach, so it's where my kids come to swim, where they would be swimming."
The shark swam around the jetty for about 20 minutes.
Water Operations police were monitoring the area and warnings were issued for swimmers to stay away.
Primary Industries and Resources SA figures show there were almost 60 shark sightings off the state's coast in January and February.
Two weeks ago, a shark was sighted 300m off Largs Bay by the UniSA fixed-wing shark spotter plane.
Mexico bans shark finning!
In a surprising move, the Mexican government has recently published sweeping new regulations and protections for sharks, including a shark finning ban, an extension of the moratorium on new commercial shark fishing permits, and extensive protections for great white sharks, whale sharks, basking sharks and manta rays...“Mexico has taken a real leadership position here” says Patric Douglas CEO of Shark Diver http://www.sharkdiver.com a shark cage diving company based in San Diego. “The rest of Latin America is watching what Mexico does with great interest now, this is good news indeed”.In the past few years Mexico has been recognized as one of the few places on the planet where large congregations of Great White sharks appear each year at Isla Guadalupe. Along with Whale shark aggregations in Holbox, destination tourism with these shark species and others is growing.Captain Mike Lever owner of expedition dive vessel MV Nautilus Explorer was thrilled at the news “The people of Mexico afford us a great privilege in allowing us to dive with the white sharks at Guadalupe Island. The February 14th enactment of Mexican rules for responsible shark and ray fisheries is incredibly good news and really bodes well for the survival of these magnificent animals. Our hats are off to all of the scientists who helped make this happen”.The new rules and regulations came after 10 years of debate and the broad support of researchers, scientists, conservations groups, eco-tour operations and local citizens.http://www.underwatertimes.com/
Diving with great white sharks
Picture the scene at Kleinbaai, a small fishing village on the furthest tip of South Africa. Between you and the Antarctic there is nothing but sea. Very cold sea. It is early in the morning, and the village, harbour and the sea are shrouded in a cold, damp sea mist, which just adds to the sense of foreboding I am feeling as I look at the people around me listening to a safety briefing about what we have come here for. We are going in a boat to find and observe great white sharks.
Freezing water viewed from the cageHighly dangerous, they grow to 21 feet (6 metres) and they are the world’s largest predatory fish. Some of the methods used by such boat trips (such as chucking dead, bloody fish in the water to attract them) are alleged to contribute to the increasing attacks by great whites on humans.
They tell us there are risks involved as we sign a wide legal disclaimer. In the back of my mind I recall in this very place a couple of years ago a furious great white shark, in attack mode, launched and landed on top of the shark cage while people were still inside it under water. Clearly there are risks involved, but they don’t mention this incident. We sit on an unfeasibly small, unsteady boat reeking of what is quaintly called “chum” which is smelly, fermenting bloody fish heads and entrails, with which the great whites are – hopefully –attracted to the boat.
It has to be bloody and smelly to tempt the sharks away from their usual meal, seals, as they patrol a place called Dyer Island, a food hypermarket for great whites, as the hundreds of thousands of seals living there frolic in the water.
On the way out we are completely enveloped in a creepy thick mist, so that neither land, mountains, islands, other ships or anything at all is visible to us. It is slightly unnerving, reminiscent of tales of the Marie Celeste as a complete, tense silence breaks out on the boat. We cut the engines after a while, the stench of the seals coming to us on the wind, their noise drifting towards us, but nothing at all can be seen.
The Shark attacks underwater, rolling its eye to whiteAll we hear is the distant, gentle break of waves, the noise of seals and the creaking of the boat. The captain pulls a festering fish head from the bucket, to much general revulsion at the stench, puts it on a hook and hurls it into the small patch of visible sea surrounding us. He trails it like a lure on many occasions at different locations over the next hour and a half, but, as nothing shows in the water, I begin to think today will be an anticlimactic waste of time.
I look at the flimsy, small dive cage resting on the back of the boat and wonder how something so delicate can keep out an angry great white and its gnashing jaws. After a couple of hours of absolutely nothing, the mist completely clears, leaving us still overcast but with a spectacular view of the distant mountains of the southern Cape, seal-festooned Dyer Island in front, and three other boats in the vicinity. Suddenly everyone cheers up and new purpose is injected into the venture. Almost immediately we had a shark contact.
From nowhere a gigantic silver mass, much bigger than our boat, slid gracefully if worryingly under the hull, circled the bait then attacked it. It missed. The shark attacked again, but the bait was pulled away. The next time it came from directly BENEATH the bait, shooting upwards like a missile launched from a submarine, and it was successful. Clearly they are resourceful and clever. Another, smaller shark joined us, and we stood on deck marveling at the sight and the size of these incredibly powerful, beautiful creatures, staring down their mouths as they breach the water to snap at the bait as it is pulled away from them.
The boat captain then lowered the cage into the cold, murky water, told us to put on our wetsuits, and jump in. I have to say I was very nervous doing this.
Great White Shark lurches at the boatI had serious second thoughts about it, but others were, so I did. Jumping into the cage, knowing you were only feet, then inches, from a great white shark, gave me an adrenalin rush, but the water was so cold my teeth started chattering and I began shivering almost immediately, and stayed that way for 45 minutes, as we stood, swam and dived in the icy water as we had more shark contacts during the afternoon.
It was absolutely freezing, but very exciting. The best contact came from nowhere - the largest great white launching a frenzied attack at the bait, which it caught right in front of the cage, inches away from our faces, so fast I could only fire of one photo, which, whilst poor, conveys something of the moment. The water became a boiling mass of foam, bubbles, blood (from the bait) masses of sharp teeth, dead eyes, and the huge silver bulk of the shark as it flashed before us at an incredible speed.
The smell of oil from the shark and the stench of the bait and the blood mingled in our noses and mouths as we sucked in seawater through our snorkels. The shark's massive body on the turn must have hit the cage at an incredible speed, as we were thrown back with great force On getting out of the water everyone was speechless. Well, not so much speechless, as uttering long sentences of expletives as our minds tried to grope for words to describe the experience we had just shared and as the adrenalin rush hit us like a train.
On the way back to land, we were kept richly entertained as another great white shark, following the boat, with its huge fin out of the water, weaved and chased an albatros's shadow on the surface of the sea, and twice it reared its head, jaws open and gnashing, to attack it, but found only water and the shadow, the albatross lazily soaring along at a safe distance above the drama. A highly recommended day out.