Climate-Challenged Whale Sharks Flocking to Island Chain
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
Whale sharks are flocking to waters off of the Azore islands, a Portuguese archipelago in the North Atlantic Ocean, a new study has found.
Whale sharks tend to enjoy warmer temperatures, but even this species has been affected by climate change, according to the study, which is published in the latest issue of the journal PLoS ONE.
It appears to be a Goldilocks effect where the sharks prefer temperatures that aren’t too hot or too cold. Things must be just right — at least for the momen t– in the Azores, which is becoming whale shark central.
Pedro Afonso of the University of the Azores and his colleagues wrote that the “occurrence of the whale shark in the wider Azores region increased drastically in 2008. Prior to this, and for a full decade, these large animals had only been sighted sporadically,” but the sharks keep coming.
Whale sharks, the world’s largest sharks, are slow-moving filter feeders known for their large mouths. They usually inhabit tropical and warm-temperate seas, preferring temperatures from 78.8 degrees Fahrenheit to 86 degrees.
In Portugal, the authors note that “whale sharks — local name ‘pintados’ — are known by Azorean fishermen to sometimes occur during the summer and associate with tuna, and have been used for a long time as an aid to locating and fishing the tuna schools.”
But the sharks have been coming even more often than that, to the point that "whale shark watching" tourism has become a growing business in the region.
The researchers analyzed a 16-year (1998-2013) observer data set from tuna fishermen around the region. They also used models to investigate the movement of the sharks in relation to factors such as food, sea surface temperature and seafloor features.
Since 2008, whale shark presence around the Azores has been steadily increasing, which appears to coincide with water temperature changes.
Usually the Azores fall into the colder side of the sharks’ preferred range, but water temperature rises at this location are proving to be a draw for sharks. Conversely, temperatures that are too hot or too cold in other spots are becoming less desirable for them.
The temperature increase in the Azores correlated with larger amounts of chlorophyll — a, a type of whale shark food.
The researchers also found that whale shark populations are higher in areas of increased seafloor slope and closer to seamounts. That’s because these regions tend to be richer in chlorophyll-a.
“Our findings underline the potential for an increase of the wider Azores region’s importance as an oceanic habitat for the whale shark in the North Atlantic in years of exceptionally high water temperature, and for a concomitant shift in the whale shark distribution within the Atlantic Ocean, as predicted by global modeling studies,” Afonso and his team concluded.
“In the future, such shifts need to be placed in the context of decadal and very long-term changes in this ocean.”
Photo: A whale shark. Credit: ThinkStock