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

Mercury concentrations in the federally endangered Western Aleutian population of Steller sea lions have doubled over the past decade, and pup levels now surpass established mammal safety thresholds in some locations. The National Science Foundation awarded a combined $1.478 million on July 23, 2026, to researchers at the University of Alaska Fairbanks and the University of Alaska Anchorage to investigate why, funding a three-year study that runs from August 2026 through July 2029.

Amanda Bishop, principal investigator at UAA, and Jennifer M. Questel, principal investigator at UAF, are co-leading the work. Bishop's portion of the award totals $208,192; she described the pup finding as especially critical. The UAF award of $1,270,264 goes to Questel's team, which will test whether zooplankton gut microbiomes are themselves producing methylmercury, the organic form of the toxin. "We hypothesize that the gut microbiomes of key zooplankton species produce significant amounts of methylmercury, thereby providing a source of this toxin in food webs," Questel said. If confirmed, that mechanism would reframe how scientists understand mercury's entry point into the marine system. To test it, researchers will sample seawater, sediments, phytoplankton, and zooplankton, and will characterize zooplankton communities along the central and western Aleutian Islands, where mercury accumulation in sea lions and other marine life varies regionally. The project is also expected to produce new information about how and where toxic mercury concentrations are increasing across the Aleutian Archipelago, and will train multiple graduate students while collecting that data.

The stakes for Aleutian communities are direct. If mercury is entering the food web at the zooplankton level and concentrating through prey species into top predators, the same pathway affects the marine species that Unangan and other Aleutian Island communities harvest for subsistence. Whether the decade-long doubling in sea lion mercury reflects a recent acceleration or a longer trend is part of what the research is designed to determine.