Shark Spring Break: Florida Swarm Explained
Sept. 5, 2012
-- Five rays and sharks are receiving priority attention at this week's IUCN World Conservation Congress held in Jeju, Republic of Korea. The congress is the world's largest conservation event. One of the five sharks is the porbeagle, shown here. Porbeagles are vulnerable globally, and are classified as critically endangered in the Northeast Atlantic. Their low reproductive capacity combined with over-fishing has led to severe population declines over several parts of its range. "Sharks and rays have traveled the Earth for more than 400 million years," said Dr. Cristián Samper, president and CEO of the Wildlife Conservation Society and keynote speaker at the Jeju congress. "Yet, in only recent decades, many of these species have become threatened from overfishing and, in some instances, have disappeared entirely from major portions of their range." He added, "The potential loss of one of only two groups of the world's living fishes is a crisis the world community must take decisive action to address. We are calling for governments around the world to vigorously support CITES international trade regulations and strengthen fisheries management and protection measures for shark and ray species. We cannot continue to allow the destruction of these wonders of evolution."
Manta Rays Fate Worse Than Sharks
The oceanic whitetip shark is critically endangered in the Northwest and Central Atlantic Ocean. It's frequently sought after for its fins, used to make shark fin soup. Usually the rest of the dead or dying shark is then tossed back into the sea. Andrew Brierley, a University of St. Andrews marine ecologist, told Discovery News that when sharks like this die off, the deaths can cause a domino effect of other ecosystem losses. Shellfish, for example, may go into decline because they are consumed more by predators that the sharks would normally prey upon. "The trophic cascade brought about by the increasing demand for shark fin soup has not only left once economically valuable bivalve fisheries in crisis, but has precipitated an ecological and culinary bankruptcy," explained Brierley.
Scalloped hammerhead sharks are endangered all around the globe. This tropical species forms large migratory schools at certain times of the year. The aggregating behavior, distinct from that of other sharks, makes the shark particularly vulnerable to fishing. "We estimate that many millions of sharks are killed annually through both legal and illegal, unregulated and unreported fishing for the trade in fins, the prime ingredient in shark fin soup," said Dr. Rachel Graham, director of WCS's Gulf and Caribbean Sharks and Rays Program. "The high price for fins has caused the global shark fishery to expand far beyond what is sustainable. The need for international regulation and enforcement has never been greater."
Shark Paradise Found
Many rays, such as these, are also in peril. The Wildlife Conservation Society and over 35 government agencies and NGO partners at the congress additionally highlighted population loss problems associated with so-called "devil rays," which feed on planktonic crustaceans. Small schooling fishes become trapped on their specialized gill rakers. Rays are frequently captured in target fisheries and as bycatch across much of their range. One reason is that the gill rakers are dried and exported for the Asian medicinal market.
Dr. Dwayne Meadows, NOAA/NMFS/OPR
The reef manta ray, shown here, is among the world's largest fishes. Both it and the giant manta ray can grow several feet across. They are slow growing, however, typically giving birth to only one pup every two to three years. They are migratory and occur in small, highly fragmented populations that are sparsely distributed across the world’s tropics. Manta rays are captured in targeted fisheries and incidentally as bycatch. In addition, manta rays are used for human consumption, shark bait, and -- as for devil rays -- are increasingly sought for their gill rakers. "The international trade in shark and ray products, including fins, meat, and other body parts, is driving shark and ray fisheries around the world, and most of these are unmanaged or only minimally managed," said Dr. John Robinson, WCS's executive vice president for Conservation and Science. "Lack of controls on fisheries and international trade puts species at risk, but also jeopardizes sustainable fisheries, ecosystems, and food security." The Convention on International Trade in Endangered Species of Wild Fauna and Flora will meet in Thailand in March 2013.
PHOTOS:Shark Teeth Weapons Reveal Surprises
The thousands of sharks that emptied Florida beaches this week are later than usual, but their purpose sounds like the usual spring break itinerary: gulping down food, having sex and seeking warmth, according to shark experts.
The dramatic aggregation consists primarily of blacktip and spinner sharks, with hammerhead, bull, lemon and tiger sharks also in the mix, according to Derek Burkholder of the Guy Harvey Research Institute and Nova Southeastern University.
"During this migration, tens of thousands of sharks are moving up the coast to waters further north where they will spend the summer months before heading back down here for the winter," Burkholder told Discovery News. "The sharks can be found very close to shore -- within a few feet -- as they follow baitfish."
George Burgess, director of the Florida Program for Shark Research based at the Florida Museum of Natural History, likens the mass grouping to people lined up to get into a football stadium. He said that sharks are actually backed up, trying to get in the warm water stream.
"Nookie is going on too," he said. "Sharks tend to mate during this time."
Both he and Burkholder remarked that the migration is happening later this year.
"Sharks are temperature dependent. The ups and downs of global climate change can affect water temps," Burgess explained.
Humans, he said, are no different, since we can tolerate some climates more so than others.
"That's why a bunch of people live in Florida, but not at the North Pole," he deadpanned.
The later migration coincided perfectly with this year’s Spring Break, when numerous college students head to beach towns to relax and party. Florida is the most dangerous state in the United States, in terms of shark attacks, and such encounters are at a 12-year high now.
The sharks in the swarm are known to bite people, but usually these are “hit and run” attacks, Burgess said. Researchers actually document these attacks to track the movement of the big shark congregation as it moves northward.
The good news is that "humans are not on the sharks' normal menu," Burkholder said, adding that it's "almost always a case of mistaken identity, especially in areas where the water is murky or near dusk or dawn, where the shark bites a swimmer thinking they are their normal fish prey."
"This is also the reason that most bites from these species are not fatal attacks," he added. "When the shark realizes its mistake, it lets go and does not continue the attack."
He and Mahmood Shivji, director of both the Guy Harvey Research Institute and Save Our Seas Shark Center USA, believe the swarm is misleading, though, since it can give the false impression that shark populations are booming.
"Just because we now see swarms of sharks does not mean there are more sharks," Shivji, who is also a professor at the Oceanographic Center, explained. "The reason we are now aware of them is because people are increasingly taking aerial pictures, which was not done until a few years ago. With all the sharks being overfished, it could very well be if such pictures were routinely taken 15 years ago, we might have seen swarms 2-3 times as big."
Nevertheless, swimmers and other recreational water users would do well to take heed. Burgess said the migration would be heading to places like the Chesapeake Bay, waters off of North Carolina, and parts of New Jersey. Some sharks might follow waterways from East to West, such as going deeper into the Gulf of Mexico.
"If you've been in such waters before, you have probably been 10 to 15 away from a shark and just didn't know it," Burgess said.