Climate change and overfishing increase the level of mercury in fish
Juan Jose Alava
Research unit on pollution of the oceans, University of British Columbia
THE SCIENCE IN HIS WORDS / We live in an era, the Anthropocene, where humans and corporations reshape and transform ecosystems. The pollution, the climate change of human origin, and over-fishing has altered the marine life and food webs of the oceans.
The increase of the temperature of the water amplifies the accumulation of contaminants neurotoxic as the organic mercury (methylmercury) in some marine species. This affects particularly the large predators, such as killer whales, which consume fish that need to feed on the large fish to meet their calorie needs.
Today, the contamination of marine life and food webs is growing because of the combined action of the mercury pollution, climate change and overfishing. This has obvious implications for ecosystems and the ocean, but also for public health. The risk of consuming fish and shellfish contaminated with mercury increases with climate change.
The mercury in the seas
From 1990 to 2010, the regulation has helped reduce global emissions of mercury from sources related to human activities, such as coal-fired plants, but this element remains present in the marine environment.
Methylmercury accumulates in the muscle tissue of fish in the whole of the food network, is “bioaccumulant” among the predators of large size and high trophic level. This is why it is more dangerous to consume large pelagic fish, such as tuna, billfish, saury and sharks, which eat a lot of fish that small.
The mercury can cause neurological disorders in humans. The young people who are exposed to mercury during fetal development and childhood have an increased risk of poor outcomes on tests measuring attention, IQ, fine motor skills and language.
Climate change may amplify the accumulation of methylmercury in fish and marine mammals at the top of the food chain due to changes in the penetration and the fate of mercury in the oceans and in the composition and structure of food webs. With the ocean warms and acidifies, one is likely to find more methyl mercury at all stages of the food chain.
Overfishing can also increase the levels of mercury in some species of fish. The Pacific salmon, squid, and forage fish, as well as the Atlantic bluefin tuna and Atlantic cod are exposed to the increase of the concentration of methyl mercury caused by the increase of the temperature of the marine waters.
Our modeling work show that the king salmon, the largest species of Pacific salmon, and the main prey of Southern resident killer whales, which are endangered species, will be exposed to a strong accumulation of methyl mercury due to changes of its power that result from climate change.