Sharks, like this recreation of Squalicorax -- identified from fossilized 100 to 72 million-year-old rocks -- have been around a long, long time. Scientists were reminded yet again of their longevity when a line of mini-sharks thought to have become extinct 250 million years ago actually survived the great dying event to live on for another 120 million years.
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
A line of mini-sharks thought to have perished in Earth's "Great Dying" event some 250 million years ago, in fact lived another 120 million years, said researchers Tuesday who found samples of their miniscule fossil teeth.
The strange creature, which measured no more than 30 centimetres (12 inches) in length and likely sported a hook-like protrusion in place of a dorsal fin, may have survived the calamity by hiding away in the deep seas, the research team wrote in the journal Nature Communications.
The planet's worst mass extinction wiped out about 95 percent of marine species and 70 percent of land species at the end of the Permian period, when Earth was believed to have had a single continent surrounded by a single ocean.
Theories for the cause of the catastrophe include an asteroid impact that smothered the planet in dust which obscured the Sun and shrivelled vegetation, or a fierce period of vulcanism that caused a lethal mixture of acid rain and global warming.
Among the creatures thought to have disappeared were Cladodontomorph sharks, distant cousins of modern sharks, which sported jaws with several rows of tiny, sharp teeth.
But now a team from Geneva's Natural History Museum and France's Montpellier University uncovered six such teeth in sediment near the southern French town of Montpellier from the early Cretaceous period, when the area would have been under water.
The teeth, less than 2 millimetres in size, were from three different Cladodontomorph species, now extinct, which lived about 135 million years ago.
"Our finding shows that this lineage survived mass extinctions most likely by... using deep-sea refuge environments during catastrophic events," said the study.