Dolphin Mystery: What's Killing Firstborn Calves?

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Northern fur seals in the Bering Sea and killer whales off the Alaskan coast also lose firstborns, said Todd Ohara, a wildlife veterinary toxicologist at the University of Alaska Fairbanks. "We're very worried about neonatal exposure. But trying to link specific contaminants [with the deaths] is difficult," he said.

Since the Second World War, more than 75,000 new chemicals have been developed and put into use according to the Washington D.C.-based Environmental Working Group. Many of these chemicals are dumped into oceans or waterways. United States law does not require chemical companies to conduct health and safety tests on their products, so no data exists for the vast majority of chemicals.

Dolphin Studies

Florida's Gulf Coast provides an excellent natural laboratory to study dolphins. Mote researchers have followed families of dolphins here for over three decades and still track about one-third of their original 47 subjects—as well as their calves, grand-calves, and great-grand calves.

"We currently have about 140 dolphins regularly using Sarasota Bay, with another 2,400 individuals roaming up and down the central west coast from Tampa Bay to Charlotte Harbor," said Wells. Studying the environmental effects of contaminants is just one of 20 studies currently underway under the Sarasota Dolphin Research Program.

The Gulf carries higher concentrations of contaminants than the open ocean, says Kucklick—and firstborn dolphin deaths are higher there, too. In a study of Atlantic spotted dolphins in pristine Bahamas waters, just 25 percent of firstborns die, says Denise Herzine, research director of the Wild Dolphin Project in Jupiter, Florida.

An Array of Toxins

Pesticides are chemicals that were designed to act on the central nervous system, explains Olson; they impair immunity and disrupt hormonal activity in the thyroid and other glands. PCBs have been linked to premature births, sterility, and other reproductive failure. "The levels are at those where we can expect to see some of these effects," said Kucklick.

PCBs are a family of 209 chemical compounds originally used as flame retardants and electrical insulators that were eventually used in products from cereal boxes and varnishes to bread wrappers until they were banned in the U.S. in 1979.

Toxic Consequences

But the effects of these chemicals can be subtle. Studies on humans have shown that PCBs affect learning and hearing development—both of which are particularly important to dolphins, famously social creatures who communicate via sound.

Lowered immunity may mean that a calf doesn't recover from a wound or minor infection. When combined with other factors, like the less-than-optimal attention of inexperienced, first-time mothers, firstborn dolphins are at a clear disadvantage. "We know much more about the effects of these chemicals in people than we do in wildlife," said Kucklick. Little is known about chemical interactions in mammals.

Last year, a study in the journal Environmental Toxicology and Chemistry pointed out that chronic exposure to PCBs hampered the reproductive success of dolphin populations in Sarasota Bay; Beaufort, North Carolina; and Matagordu Bay, Texas.

The mystery of the firstborn dolphin die-offs reflects the complexity of the species. Dolphins are highly intelligent creatures, and "nothing about them is simple," said Wells. "I wouldn't be surprised if a number of factors might contribute to the deaths."

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