Every year, elephant seals come to shore along California's coast to shed their outermost layer of skin and hair in a process called a catastrophic molt. It takes about 25 to 28 days for the entire process, during which the elephant seals are hauled out on the beach resting and sun-bathing.

Researchers noticed that during these molting periods, the mercury levels in coastal sea water skyrockets, and a recent study published by scientists at UC Santa Cruz links the uptick in mercury to the hair shed by these elephant seals.

"Compared to other coastal sites, the concentration of methyl mercury in the seawater at Año Nuevo was twice as high during the breeding season and 17 times higher during the molting season," states the UC Santa Cruz press release.

"Mercury is a problem in the marine environment because the most toxic form, methyl mercury, is readily absorbed and accumulates in the bodies of marine organisms. In a process known as 'biomagnification,' the toxin becomes more and more concentrated as it passes up the food chain. Thus, mercury concentrations in top predators can be 1 million to 10 million times higher than the levels found in seawater."

Heavy metal contamination of top predators is something that significantly affects humans as well. When we eat top ocean predators, such as tuna and salmon and sea bass, we are consuming the heavy metals that have accumulated in their flesh. Contamination is a health concern for everyone, but causes serious issues particularly in cultures living in or near the Arctic and that rely on the meat of whales, walrus and seals for food. Contaminates released by coal-fired power plants can accumulate in plants an animals in the Arctic, which are then eaten by local people. Earlier in 2015, National Geographic reported, "Inuit kids with the highest exposures to mercury in the womb are four times more likely than less-exposed Inuit kids to have low IQs and require remedial education, according to new findings by a team of researchers in Canada and the United States. The children scored on average almost five points lower on IQ tests... Previous research has suggested effects on attention disorders, motor skills, heart rates, and respiratory and ear infections."

A male elephant seal comes in from the ocean to rest on the beach. A male elephant seal comes in from the ocean to rest on the beach. (Photo: Jaymi Heimbuch)

Elephant seals stay out at sea for months at a time feeding on fish and other sea life from the California coast all the way up to the archipelago of Alaska, during which time they accumulate a lot of mercury and other contaminates. A related study published in 2015 showed that mercury levels in elephant seals are among the highest of any marine predator. "According to first author Sarah Peterson, a graduate student in ecology and evolutionary biology, 99 percent of the animals studied had blood mercury levels that exceeded the threshold for clinical neurotoxicity in humans," says the UC Santa Cruz press release.

That's why the shed hair of elephant seals can have such a significant affect on the mercury levels in the surrounding sea water. "The seasonality of the methyl mercury levels at Año Nuevo implicates molted pelage as the main source. According to Cossaboon, the dramatic increase in methyl mercury in the water during the molting season resulted in levels greater than those observed even in the highly urbanized San Francisco Bay estuary."

What exactly the high levels of accumulated mercury means for the health of elephant seals is unknown, as the researchers point out that it is extremely difficult to study neuroactivity in humans, let alone wild animals, let alone a wild animal that can grow to 13 feet long and weigh 4,500 pounds.

And what exactly this means for the surrounding environment is still a question mark as well, though one thing is certain: you should probably skip swimming in nearby water during elephant seal molting periods.

Jaymi Heimbuch ( @jaymiheimbuch ) focuses on wildlife conservation and animal news from her home base in San Francisco.