Mercury in Western Aleutian sea lion pups exceeds safety thresholds, prompting $1.5M NSF study

Mercury in the endangered Western Aleutian population of Steller sea lions has doubled over the past decade, and in some places the pups now carry more than the level considered safe for mammals. A new $1.5 million federal study will try to find out why.

The leading suspect is a surprise: the gut microbes of zooplankton, the tiny animals near the base of the food web. Researchers suspect those microbes are producing methylmercury, the toxic form that builds up as it moves through prey into top predators. If that holds up, it would rewrite where scientists thought the toxin enters the ocean. To test it, University of Alaska teams will sample seawater, sediment, and plankton across the Aleutians, where mercury levels vary from island to island.

The stakes reach past the sea lions. The same food web feeds the fish and marine mammals that Unangan and other Aleutian communities harvest for subsistence. If mercury is entering low and concentrating upward, it is moving toward the same table people eat from. The three-year study runs through 2029.