Biologist Steve Mierzykowski holding a sturgeon. Sturgeon, which appeared in the fossil record about 200 million years ago, are covered with bony plates called scutes, rather than scales. Credit: USFWS

Bottom-feeding fish exposed to mercury in food and sand

The Problem and Effects:
The Atlantic sturgeon and shortnose sturgeon, both endangered species in the northeastern U.S., are bottom feeders that forage for small clams, invertebrates and fish by sucking up large amounts of mud and sand. The sturgeon's feeding method not only exposes them to contaminants in their prey but also contaminants within the sediment.

DDT was a major reason for the decline of the bald eagle in North America in the 1950s and 1960s. DDT and its breakdown products, DDD and DDE, are toxic to embryos and disrupt calcium absorption and impair eggshell quality.

What We're Doing:
Since 2007, the Fish and Wildlife Service measured contaminant levels in sturgeons found dead in Maine's large rivers and along the Massachusetts coast. Fortunately, highly elevated levels of organic contaminants, such as PCBs and metabolites of the pesticide DDT, have not been found in sturgeon tissues.

However, mercury levels in muscle tissue from shortnose sturgeons Maine were elevated compared to tissue threshold effect levels and similar to concentrations found in Maine's freshwater predator fish species like bass and pickerel.

Three reports on contaminants and sturgeon are available online here.

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