Black guillemots, seabirds with coral-colored legs and a prominent white spot on their feathers, are iconic figures along the cliffs of Acadia National Park and the coastal North Atlantic.
Their more important role is as a sentinel species — a canary in a coal mine — in the Gulf of Maine to indicate levels of mercury in the fish they eat from the sea. The black guillemots, readily visible darting through the air or perching on rock faces, have higher mercury levels than some other birds, partly because of the type of fish they eat, a recent Dartmouth College study in the journal Science of The Total Environment found. The levels have not yet resulted in fish consumption warnings for humans, but the seabirds are at risk for mercury poisoning.
“The black guillemots have mercury levels in their contour and down feathers that could potentially put them at risk,” said Celia Chen, a research professor at Dartmouth in New Hampshire and an author of the study. “It won’t kill them, but they could have reduced reproduction.”
Some of the black guillemots had mercury levels above 30 parts per billion, she said, the level at which the metal causes toxic effects in other seabirds, including having fewer chicks and possibly shortening their lifespan. The scientists studied the down and body feathers of the chicks of black guillemots, the common tern and endangered roseate tern.
The Dartmouth study focused on where the seabirds eat nearshore in the Isles of Shoals, a group of islands about 6 miles out to sea straddling the border of Maine and New Hampshire, for clues about mercury buildup in the animals. The study found that their diet and the ocean level where their prey dwell make a difference in their mercury levels.
Black guillemots have concerning levels of mercury, while the two tern species do not, the study found.
The black guillemots eat larger fish, including butterfish and sculpins, than the terns. The larger fish generally have accumulated more mercury because they eat smaller fish that contain mercury, and the chemical builds up in the food chain, Chen said. The black guillemots also dive down into the sea — some 100 feet or deeper — to get fish, which are more exposed to mercury trapped in the sediments. Terns eat fish attainable closer to the water’s surface.
“We want to find out if these animals in our environment are at risk,” Chen said. “A healthy seabird population is important because these species have an important role in the food web.”
Mercury levels increased in seabirds that foraged for fish close to the shore in the Gulf of Maine between 2008 and 2013, a separate study in the Marine Pollution Bulletin released in 2018 found. The study also found that atmospheric emissions of mercury have decreased in the past 20 years, but mercury still is rising in the northeastern United States and the Arctic.
Mercury is a poisonous, naturally occurring chemical element that does not break down in the environment. It is transported through the atmosphere from coal-fired industrial plants in the U.S. midwest and Canada. Rainwater distributes it in the ocean and freshwater bodies. Mercury turns into its more toxic form, methylmercury, when it interacts with organic matter in sediments. It stays in the environment unless removed by dredging or the natural, long-term diffusion by ocean and other waters.
It is difficult to get rid of: The Penobscot River will soon undergo a $187 million cleanup to remove mercury dumped by an industrial plant.
Mercury levels in Maine’s fish, loons and eagles are among the highest in North America, according to the Maine Department of Environmental Protection. The levels are less concentrated in seabirds but are still of concern.
“There are elevated levels of mercury in most all birds, but the questions are if those levels are hitting some sort of adverse effects for those species or causing some sort of population harm,” said David Evers, executive director and chief scientist at the Biodiversity Research Institute in Portland. Evers has been involved in other research published on mercury in seabirds.
Mercury levels have been higher in Maine and the Northeast because of historic industry and pollutants from elsewhere in the country flowing to the region. Maine’s ecosystems also tend to make methylmercury more prevalent. Mercury that gets to Iowa’s dry corn and other farmlands will not turn into as much methylmercury as when it gets into a bog or lake in Maine, where it can turn into methylmercury more easily and cause problems, Evers said.
The U.S. federal government is not funding regular studies of mercury in fish and wildlife across the country, Evers said, although the country has created regulations to reduce mercury. Examples are the Clean Air Act that regulates emissions and the Mercury and Air Toxics Standards, aimed at electric utilities, that set emission standards for mercury and other hazardous air pollutants for any plant with a capacity of more than 25 megawatts.
Evers and Chen said regular monitoring of mercury in seabirds could help better understand the effect of these measures. But some sources of mercury pollution remain out of control for the federal government, notably mercury emissions from mining in Africa, Asia and South America.
“Those types of regulations can really reduce the amount of atmospheric emissions that end up being transported all over the globe and then ending up in pristine systems,” he said.
Interest in studying mercury in the environment has risen since the Minamata Convention on Mercury, an international agreement among more than 140 countries adopted in 2013. It aims to protect human health and the environment from mercury. The convention is named after Minamata, a city in southeastern Japan where a chemical factory discharged mercury for 36 years starting in 1931. More than 900 people died, and another two million who consumed contaminated fish have had neurological and other health problems, according to The Lancet journal.
Chen and Evers said the Dartmouth study contributes to knowledge of how much mercury is concentrated in birds, fish and marine mammals, and whether the levels are high enough to cause health concerns for those animals and people.
“If the black guillemot levels are extremely high, that would tell the state or federal authorities to avoid eating fish for people in those areas,” Evers said. “But the levels are not high enough to worry about, yet.”
Lori Valigra is an investigative environment reporter for the BDN’s Maine Focus team. She may be reached at [email protected]. Support for this reporting is provided by the Unity Foundation and donations by BDN readers.
