Coastal fog linked to mercury poisoning in mountain lions, researchers say


Coastal fog may be carrying toxic levels of methylmercury, which is then dumped on the land and makes its way up the food chain and contaminates mountain lions living in the region, according to a study by UC Santa Cruz researchers.

In a study published last week, researchers found that methylmercury levels were three times higher in mountain lions living along the coast than among those in inland areas. The increased toxin levels could threaten the big cats’ survival and reproduction as they struggle to navigate their increasingly populated habitats.

Mercury is a naturally occurring pollutant that is released into the environment through mining and coal-fired power plants. It’s so widespread that almost everyone has small amounts of the neurotoxin in their system, according to the Environmental Protection Agency. Humans are typically exposed to the chemical when they eat fish and shellfish.


However, at high levels, the toxin can cause neurological damage and decrease fertility.

UC Santa Cruz researchers — including lead authors Chris Wilmers and Peter Weiss-Penzias — examined fur and whisker samples from 94 coastal mountain lions and 18 noncoastal mountain lions for the study. At least one animal had mercury levels known to be toxic to species such as mink and otters, and two other mountain lions had sublethal levels that reduce fertility and reproductive success.

Lichen and deer in the fog zone also had significantly higher mercury levels than those in inland areas.

Researchers explained that lichen don’t have roots, so the methylmercury in the fungus must come from the atmosphere. The lichen and deer are consumed by predators, and as the neurotoxin makes its way up the food chain, its concentration can increase 1,000 times, making top predators vulnerable to the chemical.

“We need to protect the top predators in the environment,” said Weiss-Penzias. “They’re keystone species. They perform ecosystem services. When you change one thing, it has cascading effects through the system.”

Mountain lions keep deer and small predators in check, which in turn, reduces Lyme disease. The extinction of the animals locally could be disastrous, Weiss-Penzias said.

In Southern California, the big cats are facing additional challenges compounded by their urban habitat. Since the National Park Service began its study of the animals in the Santa Monica Mountains in 2002, five mountain lions have died as a result of rat poisoning.


A handful of others have been diagnosed with mange, which researchers think is linked to the rat poisons. Researchers don’t fully understand the nature of the link between rat poison and mange but have said it’s likely that rat poisons weaken the cats’ immune systems, making them more susceptible to the skin disease.

In addition, the freeway systems interrupting the lions’ mountainous habitats are making for killing fields. Several mountain lions have died attempting to cross major freeways, and those that don’t risk the venture are forced to mate with their own offspring, making for a smaller genetic pool, sterility and health problems that threaten the big cats’ survival.