Dead Risso's Dolphin on Norwick beach This dolphin had its tail tangled in a discarded fishing net, presumably the cause of its death.Mike Pennington, Wikimedia Commons
- Numerous mass deaths of dolphins have occurred over the past few years, but experts say we are not witnessing a global population crash.
- Unlike the fungus decimating multiple North American bat species, no single factor causes different dolphins' dilemmas.
- Experts have tips for how to lead a dolphin-friendly life.
Several mass deaths of dolphins have occurred over the past few years and while experts are worried about the die-off they say we are not witnessing a global population crash.
But what is behind the resent mass strandings and deaths is complicated and, inevitably, involves humans.
For example, the bottlenose dolphin die-off in Gulf of Mexico started in early 2010, even before BP's massive oil spill in April 2010. Disease was linked to some of the hundreds of Gulf dolphin deaths, but not all of them. The ultimate cause remains mysterious.
"There is no evidence at this time to indicate that such a world-wide, multi-species crash is occurring," Randall Wells, director of the Sarasota Dolphin Research Program said. "The large scale mortality events and mass strandings that have made the news in the past two years appear to be unrelated."
Nonetheless, the past two years have been rough for several species of dolphins, but not all of the nearly 40 species of dolphins are in hot water.
"There is not a large scale die-off of dolphins across the globe or throughout ocean basins," said Connie Barclay, spokesperson for the National Oceanic and Atmospheric Administration (NOAA)'s National Marine Fisheries Service.
"What we do see are localized areas where strandings and deaths have increased," Barcaly said. "Scientists have seen unusually high rates of illness and death in specific populations of bottlenose dolphins in the Gulf of Mexico, long-beaked common dolphins along the beaches of Peru and short-beaked common dolphins along the shores of Cape Cod."
And only certain populations of the effected species have been hit hard.
"While bottlenose dolphins in the northern Gulf of Mexico are dying at higher-than-average rates, elsewhere in the Gulf of Mexico bottlenose dolphin populations are doing fine," Wells, a former chair of NOAA's Working Group on Marine Mammal Unusual Mortality Events , said.
One population that suffered a serious dolphin disaster swam in the Pacific off the coast of Peru. Discovery News recently reported on the thousands of dolphin corpses washing up on the tropical beaches.
"The Peru mass stranding is the largest ever reported in the [Western Hemisphere] and the biggest since the mass stranding in Europe during the '90s," Carlos Yaipen-Llanos, president and science director for Organization for Research and Conservation of Aquatic Animals (ORCA).
The causes of the dolphin strandings and deaths seem to be varied as well. Unlike the fungus decimating multiple North American bat species, no single reason has been found for the dolphins' dilemma.
"No common infectious disease has been identified in any of the current dolphin stranding events," said Barclay. "Scientists are still working to understand the local and global effects of changing environmental conditions on marine mammal populations."
When these mass deaths occur, whole family groups can be wiped out, said Yaipen-Llanos. The effect on the future of the species when whole generations of dolphins are wiped out is a serious concern to dolphin research and conservationists.
Ocean-going dolphins are not the only ones suffering. The Chinese river dolphin, or baiji, was declared functionally extinct in 2006 after an study couldn't find a single individual.
The baiji was probably done in by a combination of problems caused by humans, including accidental deaths by getting trapped in fishing gear, vessel strikes, underwater explosions, excessive noise and depletion of prey species, according to Tim Ragen, executive director of the U.S. Marine Mammal Commission.
"Broadly similar threats face marine dolphins," said Ragen.
Other possible accomplices in the dolphins' demise were abnormal weather, toxic algae blooms, parasites, pollution exposure, loss of prey leading to starvation, disorientation due to loud noises from ships and oil exploration and physical injury.
"In many cases, the cause of stranding is unknown and difficult to discern," said Barclay.
What isn't in doubt is that human impacts on the ocean are hurting dolphins around the world.
"People should recognize that the dolphins need the waters to survive -- that we are visitors to their homes," said Wells. "As visitors, we should be good stewards, and respect the needs of these animals as they try to make a living in the aquatic environment."
Everyday choices can affect the fate of the dolphins. Dolphin experts have some suggestions for how to lead a dolphin-friendly life.
"No matter where you live, reducing pollution can help these animals, as chemicals such as PCBs can be transported by air for thousands of miles before being deposited into the marine environment," said Wells.
Wells also warned against the illegal but popular practice of feeding wild dolphins. The practice brings dolphins closer to the dangers of being struck by boats or tangled in fishing lines and disrupts the animals' social groups.
"When voting or otherwise participating in the political process, insist on transparent and environmentally responsible decision-making," said Ragen. "Inform your political leaders that you support fisheries and other human activities in the marine environment that are seeking to minimize their impacts and promote better ecosystem health, such as reductions or elimination of gillnet fisheries with bycatch problems."
Ragen noted that reducing consumption in general is good for dolphins and other sea life. A major cause of habitat degradation is the increasing volume of shipping traffic which fills the sea with the thunder of engines and churning water.
"The overall picture for dolphins and other marine and aquatic wildlife is not very promising -- witness the massive over-exploitation of fish stocks, the huge expansion of larger, faster, and louder ships, the rush to develop offshore oil and gas, and the apparently intractable problems of climate disruption and ocean acidification," Ragen said.