Sharks Do Get Cancer: Tumor Found in Great White
A tumor found in a great white shark is the first ever documented in this species.
Scientists have known for more than 150 years that sharks get cancer. And yet the belief persists that the animals don't suffer from the disease.
That misconception is promoted in part by those who sell shark cartilage, who claim that the substance will help cure cancer, said David Shiffman, a shark researcher and doctoral student at the University of Miami. But no studies have shown that shark cartilage is an effective treatment, and the demand for the material has helped decimate shark populations, researchers say: Humans kill about 100 million sharks per year, according to a March 2013 study (although many factors contribute to the killing of sharks, including demand for shark-fin soup).
Recently, researchers in Australia noticed a large tumor protruding from the mouth of a great white shark, as well as another mass on the head of a bronze whaler shark. The great white's tumor measured 1 foot (30 centimeters) long and 1 foot wide, according to a study describing the tumors published online in November in the Journal of Fish Diseases.
"This was a very unusual sight as we have never before seen a white shark with tumors," said Rachel Robbins, a study co-author and shark biologist at the Fox Shark Research Foundation, near Adelaide, in southern Australia. [Image Gallery: Great White Sharks]
In total, scientists have now documented tumors in at least 23 species of sharks, including the two in the new study, Robbins said. "The main take-home message from the study is that it adds to the growing evidence of tumor formation in sharks, contrary to popular belief that sharks do not suffer from such anomalies," Robbins told LiveScience.
"Sharks get cancer," said Shiffman, who wasn't involved in the study. "Even if they didn't get cancer, eating shark products won't cure cancer any more than me eating Michael Jordan would make me better at basketball."
The belief that shark cartilage can treat cancer diverts patients from effective treatments, according to a 2004 review in the journal Cancer Research. The demand for cartilage also fuels widespread fishing for sharks. One in six known species of sharks, rays and skates are considered threatened with extinction by the International Union for Conservation of Nature, an environmental group, Shiffman said.
It's unknown what caused the tumors in the great white or bronzer shark. However, reports of cancerous tumors in marine animals, especially mammals, have steadily increased over the past 20 years, raising concerns that industrial pollutants or human activities may trigger the cancers, according to the study. Beluga whales have been recorded to suffer from cancer, and in areas near aluminum smelting plants, cancer is the second leading killer of the whales, the study noted.
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A tumor appears on the lower jaw of a great white shark, near the Neptune Islands, South Australia. It's the first documented tumor in this species.
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.
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.
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