Something in the Water

Salmon are transporting pollutants to streams, and the harmful chemicals are being taken up by other fish, researchers have discovered. Some of these stream-dwelling fish, such as trout, may need monitoring to ensure they don’t threaten the health of people who eat them.

It’s well-known that migrating animals can carry pollutants from one area to another. Pacific salmon, for example, eat prey containing persistent organic pollutants (POPs) in the ocean. When the salmon swim to streams to spawn, they bring their chemical baggage with them.

A team of researchers wondered if other fish in the streams were picking up these contaminants from salmon. They collected brook trout, white suckers, and other fish from tributaries of the Great Lakes, where salmon spawn each year. Some fish came from parts of the stream with salmon, while others were sampled from areas cut off from the spawning.

Fish that shared the stream with salmon had much higher POP levels than those in salmon-free areas, the authors report in Environmental Science & Technology. In the Lake Michigan tributaries, pollutant concentrations were 8 to 29 times higher in the fish from salmon-spawning segments; in Lake Huron tributaries, the pollutant levels were 6 to 12 times higher.

If managers remove dams that currently separate parts of the stream from salmon spawning, even more fish could be exposed to the contaminants. Bald eagles also feast on salmon in those tributaries, the team notes.

The findings could be worrisome news for people who eat the fish in these streams. Managers may need to keep a close eye on pollutant levels “to alert consumers of potential health risks associated with consuming trout from streams receiving salmon runs,” the authors say. Roberta Kwok | 25 July 2012

Source: Janetski, D.J. et al. 2012. Resident fishes display elevated organic pollutants in salmon spawning streams of the Great Lakes. doi: 10.1021/es301864k.

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