Yes, you read correctly. When Northern elephant seals (Mirounga angustirostris) moult, they don’t only shake off excess fur: they also shed methyl mercury accumulated in the pelt, polluting the surrounding area.

Methyl mercury is a highly toxic aquatic substance often found in fish, and has largely been attributed to industrial pollution. Because aquatic organisms can’t shed this substance easily through biological functions, it moves from one organism to another, making larger fish species more likely to carry high quantities of it.

Princeton University researchers took it on themselves to see whether marine mammals contribute to polluting their ecosystem, while also falling victim to this substance.

What they found is quite amazing. Methyl mercury levels around the area where Northern elephant seals shed their fur and first layer of skin increase quite substantially during moulting periods. This means that the methyl mercury buildup accumulated during feeding periods is expelled into the ground and ocean, and will directly influence the ecosystem around the seals.

Methyl mercury levels were found to be 8 times higher than average, and sometimes even 31 times more during the Northern elephant seals’ moulting period.

What does this mean? It could be possible that the methyl mercury pollution will keep re-entering ecosystems to the detriment of the organisms that live in them. “It’s important to be aware of this phenomenon, just so we know where to identify those hot spots,” co-author Jennifer Cossaboon told