Every tasty tuna sandwich or casserole includes an unwanted serving of the highly toxic metal mercury. So we welcome a new report that shows Gulf of Maine tuna are becoming safer to eat as mercury-laden emissions from coal-fired power plants have declined – and we urge Maine’s congressional delegation to resist efforts to roll back the policies that have made this progress possible.

The good news comes out of a study published last month by researchers at Harvard, the University of Massachusetts and Stony Brook University in New York. Looking at samples of nearly 1,300 bluefin tuna caught in the Gulf of Maine from 2004 to 2012, the scientists found that levels of mercury in the bodies of the fish fell by about 2 percent each year, or nearly 20 percent over a decade.

The decline occurred as coal-fired power plants in the Midwest began going off line or switching to natural gas in 2008, responding to market forces and regulatory and industry curbs on emissions. The relatively quick level of improvement came as a surprise, Stony Brook’s Nicholas Fisher, study co-author, told Scientific American.

That’s because tuna – the biggest source of mercury in the American diet – are a big, long-lived, predatory species that can accumulate a lot of mercury from eating other fish. So although the tuna that were studied still weren’t safe to eat, it bodes well for the future that, as Fisher said in an interview with The Washington Post, “the fish are responding almost in real time” to environmental changes.

But these hard-won gains could easily be reversed if President-elect Donald Trump acts on his pledge to halt measures to address climate change. Of particular concern is his proposal to abandon the Paris agreement, which commits the U.S. and 192 other countries to individual carbon pollution limits, and to roll back the Clean Power Plan, an Obama administration initiative that sets the first-ever limits on carbon pollution from power plants.

If Trump dismantles this and other pollution curbs, Maine could be hard hit. Not only could the benefits to the tuna fishery be at risk, but we’d be stymied in addressing our rate of asthma, which is among the nation’s highest and is aggravated by unchecked out-of-state carbon emissions.

Mainers have made it a priority to limit air and water contamination from sources here. Our elected representatives in Washington should make it clear to the incoming administration that we have no appetite for measures that allow other states to abdicate their responsibility to do the same.