Mysterious New Mexico Elk Deaths Explained

October 30, 2013

Sante Fe New Mexican

For 100 elk, it was just the wrong place, wrong time.

Pond scum — the bluish-green algae that blooms naturally in warm, standing water — killed more than 100 elk in late August on a private northeastern New Mexico ranch, according to the New Mexico Department of Game and Fish.

Traces of Anabaena, one type of blue-green algae that can produce a deadly but short-lived neurotoxin, anatoxin-a, was found in a water sample from a fiberglass livestock tank near where the elk died.

“I think they spent morning feeding,” said Kerry Mower, a wildlife disease specialist with the New Mexico Department of Game and Fish. “Then, as ungulates will do, they went to rest. They stopped to take a drink on the way. The trough was in a sort of natural corridor that goes to shady trees on a hill.”

The trough was one of three fiberglass tanks that contained traces of the blue-green algae, according to water tests conducted later. Earthen water catchment tanks in the area tested negative.

A hunter on Aug. 27 found the dead elk scattered across less than a mile on the Buena Vista Ranch, north of Las Vegas, N.M. Mower said the elk death case was the largest animal die-off he’s seen.

Game and Fish investigated the case, and department staff, as well as pathologists from veterinary diagnostic labs where tissue samples were tested, ruled out a broad range of other possible causes of the elk deaths: anthrax, epizootic hemorrhagic disease, botulism, lightning strike, poaching, pesticides and malicious poisoning.

“We couldn’t find anything [toxic] in their stomachs and no toxic plants on the landscape,” Mower said.

Department biologists who initially counted the dead elk suspected that they had died within a 24-hour period. Anatoxin-a can sicken or kill an animal within four to 12 hours after it has been ingested. It appeared the elk had struggled on the ground, also a symptom of neurotoxin poisoning.

The elk carcasses were left where the animals fell. Bears, ravens and vultures soon left nothing but a pile of bones, Mower said.

Blue-green algae is a microscopic cyanobacteria. The algae thrives on water that is warm and stagnate, such as in ponds, lakes and livestock tanks. Not all algae produce toxins, but all do use up the oxygen in water and choke out other aquatic plants. Algal blooms can be blue, green brown or red. A combination of factors — warm temperatures, nutrients and sunlight — can prompt an algal bloom, according to the National Oceanic and Atmospheric Administration.

Temperatures in the few days leading up to the elk die-off ranged in the mid-'80s to 90 degrees Fahrenheit, not unusually hot, according to National Weather Service data. But enough warm sunny days and clear, stagnant water can launch the algal bloom, Mower said.

Anatoxin-a was first identified in the 1960s after herds of cattle in Canada died. Studies have found it takes little of the toxin to kill an animal.

Toxins from blooming pond scum can be harmful to people as well as animals. The New Mexico Department of Health has an information bulletin devoted to health effects from algal exposure. People who come in contact with algae while swimming or wading can develop rashes and skin blisters. Swallowing the water can cause diarrhea, vomiting and neurotoxic symptoms such as tingling fingers, dizziness and, in rare cases, death.

The Department of Health said no human in the state has died from ingesting blue-green algae, but several dogs reportedly have died after drinking algae-laden water.

Another large die-off of big game occurred in 2004, when more than 400 elk died in Wyoming over a couple of months after eating lichen.

Department of Game and Fish officials said no one has reported dead livestock or wildlife in the area since August. Hunters should not harvest animals that exhibit unusual behavior or appear sick, and should report anything unusual to the department’s toll-free information line, 888-248-6866.

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