NMFS Northeast Fisheries Science Center

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"We know that low pH can be harmful to smolts," said John Magee, one of the biologists conducting the experiment at the Wild Salmon Resource Center and Pleasant River Hatchery. (Smolts are young salmon that migrate to the ocean.) "A number of studies have shown that smolts exposed to acidic fresh water are less likely to survive the transition to salt water," Magee said.

Those studies were conducted in Norwegian rivers and in fish hatcheries. In both cases, the fish were exposed to a constant low pH.

"But that's generally not what happens to salmon in Maine rivers," Magee said. "In Maine, the pH drops periodically, when snow melts, for example, but then it rises again. So we need to know whether relatively short-term ‘pulses' of low pH have the same harmful effect on smolts."

The study is a joint project of the National Marine Fisheries Service (NMFS) and the Downeast Salmon Federation, a private organization that runs the Pleasant River Hatchery at Columbia Falls. NMFS biologist Mariska Obedzinski and Pleasant River Hatchery Manager Dwayne Shaw are also working on the project.

The pH fluctuations salmon typically encounter in Maine rivers are not lethal immediately. The fish may appear healthy while they are still in the fresh water environment, but biologists think the pulses of low pH can damage the salmon's gills and compromise its ability to regulate the amount of salt in its cells. This damage may become more apparent when the smolt encounters salt water, either killing it outright or weakening it enough that it does not survive the transition to seawater.

In the study that began in early April, biologists held smolts in three tanks in the Pleasant River Hatchery. One tank is a control, in which the pH was monitored and kept at a high (or non-acidic) level. One tank was kept at low pH. The pH in the third tank was lowered for two days every week, to simulate the pulses of acidic water smolts typically encounter in the Pleasant River.

On Monday, some of the smolts from each tank were placed in salt water so biologists can determine how well they adapt to salt water life. Throughout the experiment, biologists have been analyzing gill and blood samples to measure physiological changes resulting from different amounts of exposure to acidic fresh water.

Shaw said the collaborative project is the type of creative partnership needed to answer questions about fisheries declines. "The public is supportive of research, especially when people in the affected communities are involved in the studies," he said.

The Downeast Salmon Federation represents four Washington County fish and wildlife conservation organizations: Two Rivers Atlantic Salmon Club, Denny's River Sportsman Club, Pleasant River Fish and Game Association, and Narraguagus Salmon Association. The federation is working to preserve and restore wild populations of Atlantic sea-run salmon in the rivers of Eastern Maine.

The National Marine Fisheries Service manages living marine resources in federal water. NMFS conducts multi-disciplinary research programs to provide scientific and technical information necessary to manage living marine resources.