The Surprising Way Marine Mammals Are Poisoning California Condors
More than 40 years after being banned, DDT has reared its ugly head again.
Somewhere along the beautiful coast of Big Sur,听a California Condor听sinks its beak into the decaying flesh of a dead sea lion. It鈥檚 a gruesome sight, but it's not unusual鈥攅ven 10,000听years ago听condors were feasting听on the carcasses of washed-up marine mammals. The difference between then听and now听is that today's听deceased pinnipeds听come chock-full of harmful toxins, the rotting legacy of decades of poor environmental regulations in the United States.
It's theorized that听beached mammals might听have actually kept condors from going extinct at the end of the Pleistocene, when听they were steadily听deprived of the听corpses of prehistoric land animals such as听mammoths, sabercats, and giant sloths. But new research published last month in suggests that those marine scraps could听now be putting the endangered vultures at greater risk听by exposing them to an old,听familiar foe for conservationists: DDT.
Because sea lions听are at the top of the marine foodchain, they鈥檙e often tainted with toxins that are found in fish, cephalopods, and other aquatic prey. Among those contaminants is the pesticide听DDT, 听which was听dumped in large quantities听off of the Los Angeles听coast between the 1940s and the 1970s. Scientists think that听all California sea lions may be vectors of the poison, given that they swim these waters as they head to the听Channel Islands each year to breed.
To see if condors were ingesting DDT and other contaminants associated with marine mammals (like fire retardants), UC San Diego ecologist Carolyn M. Kurle and her team analyzed and compared the blood collected from coastal and inland condors during routine health work-ups. They also checked the blubber of dead听pinnipeds and whales听in Monterey County, California.
As expected, the coastal birds posted significantly higher levels of contaminants than the inland individuals. Another听听revealed that the coastal condors are laying eggs with thinner shells than their inland counterparts, causing them to be听20 to 40 percent less successful听reproducing.听
This development is听just another听setback in the efforts to restore听the听large, charismatic bird's populations.听In 1987, there were only听22 California Condors left听alive in the world. But by the mid-1990s, scientists were releasing their captive-reared descendants back into the wild. Today there are more than 400 of the birds in captivity and the wild. The species鈥 range now extends throughout California, as well as Arizona, Utah, and Baja California, Mexico.
Despite this success,听there are still many roadblocks to the condor鈥檚 comeback鈥攖he main one being听lead-based ammunition, which the birds consume while scavenging on bullet-ridden carcasses. Lead wreaks havoc on the vultures'听digestive system, causing the animal to听听to death. In the past, condors living near Big Sur were thought to be at lower risk of lead poisoning because they have the advantage of being able to feed on marine mammals. Indeed,听听published earlier this year confirmed that individuals found听on the coast tend to听live longer听than those that stick to inland habitats.听
While lead ammunition can at least听be听eliminated from the ecosystem (California, for example, is ), there's not much to be done about the pollutants that persist in the waters long after they've been restricted.听Kurle hopes that this research will underscore the long-term consequences of harmful听pesticides听by exposing their听effect on a beloved and imperiled species. "These things have been banned since the 1970s, but they're still wreaking havoc environmentally,鈥 she says. 鈥淲hat are we doing now that we're going to be paying for in听the next 50 years?"