During their molting season, the concentration of methyl mercury in the seawater at Año Nuevo State Reserve was 17 times higher than normal. Scientists then found the toxin inside the shedded skin and hair that had been taken for analysis.

The mercury in the elephant seals comes from the fish and mussels they consume, which themselves have been exposed to high mercury levels in the seawater.

Biomagnification

As the elephant seals are the top predator, the mercury inside their bodies become much more concentrated. This is due to a process called biomagnification, whereby the toxin becomes more concentrated as it moves up the food chain. As a result, the mercury concentration for elephant seals can be 1 million to 10 million times higher than the levels found in the seawater.