Bluefin tuna in the north Atlantic are showing decreasing mercury levels over the last 25 years, and reduced industrial usage in North America is being proposed as the cause. Mercury is a neurotoxin that can damage the human nervous system, and is known to build up in the tissues of organisms at the top of the marine food chain such as Tunas.
WebMD.com recently reported, "Although increased coal burning in Asia has raised mercury emissions globally, levels have fallen in North America 2.8 percent a year between 1990 and 2007, the researchers said." The article went on to state, "Over a similar period, mercury in north Atlantic waters dropped 4.3 percent annually. And mercury in the air above the North Atlantic Ocean declined 20 percent from 2001 to 2009, the researchers said."
The originating study, published by the Journal of Environmental Science and Technology, made waves in the press by making the encouraging observation that, "Notably, this decrease parallels comparably reduced anthropogenic Hg (Mercury) emission rates in North America and North Atlantic atmospheric Hg0 concentrations during this period, suggesting that recent efforts to decrease atmospheric Hg loading have rapidly propagated up marine food webs to a commercially important species. This is the first evidence to suggest that emission reduction efforts have resulted in lower Hg concentrations in large, long-lived fish.
While certain species of Tuna like False Albacore are considered a favorite saltwater target for Northeast fly fishermen, the study was limited to Bluefin tuna, one of the largest and most pelagic --or wide roaming -- species. Both species are pursued as food fish by commercial and sports fishermen.
The National Institutes of Health (NIH) has published reams of peer-reviewed data, on mercury as a global contaminant and public health risk, much of which has been involved in supporting policy formation. Recently, the UN Environmental Program led 128 countries to negotiate and sign a legally binding agreement -- the 2013 Minimata Convention -- to control mercury emissions and releases to land and water globally.
It bears noting when measurably positive effects in the environment are being backed up by science -- whether due to either enforced policy initiatives or economically driven practices that are just moving away from old technologies. While data does not exist at this time for changes in concentration of tissue contaminants in other marine species, the potential for improvement across the board may well be worth researching. Atlantic Salmon that use the North Atlantic as a maturing grounds are on the rebound in both Canadian and Icelandic rivers, and reduction in a globally endemic agent that could potentially affect critical survival behaviors such as geolocation and spawning stream homing identification may be benefitting species that split their time between fresh and salt water.