Fish species high in mercury

A diet heavy in cod may be bad for seals, a study recently published in Environmental Science and Technology suggests.

After more than 30 years of monitoring seals near the Northwest Territories community of Uluhaktok, researchers say the amount of the poisonous nerve toxin mercury in seals is connected to duration of the sea ice cover and what the seals eat.

Mercury comes from coal-burning power plants in the South, travels north and accumulates in fish.

When there is less sea ice or more sea ice than average, the mercury in seals goes up- and this is likely linked to the amount and age of the cod eaten by the seals, the researchers say.

Cod is the most-mercury-contaminated food that ringed seals eat, with older cod being the most contaminated.

In years with less sea ice, seals have a longer ice-free period when they can catch cod, and there may be more cod to eat, so the amount of mercury the seals eat increases, researchers say.

But when sea ice remains frozen longer, young cod may have a harder time surviving, leaving older and more contaminated cod for the seals to eat.

Gary Stern, a study co-author from the Univ. of Manitoba, said the trend towards less sea ice due to rising temperatures in the Arctic means that mercury in ringed seals may increase over time.