"For years, public health experts have warned against eating certain kinds of fish, including tuna, that tend to accumulate mercury. Still, tuna consumption provides more mercury to U.S. consumers than any other source. But recently, as industry cuts down on its mercury emissions, research has found mercury concentrations in some fish are dropping."
"Mirroring A Drop In Emissions, Mercury In Tuna Also Declines"
Source: Science Daily, 11/15/2016