Climate change and overfishing increase the level of mercury in fish

Les changements climatiques et la surpêche font augmenter le niveau de mercure dans le poisson

Les changements climatiques et la surpêche font augmenter le niveau de mercure dans le poisson


July 24, 2020 12: 38:


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.

Les changements climatiques et la surpêche font augmenter le niveau de mercure dans le poisson

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In the most pessimistic scenario in terms of climate change, where greenhouse gas emissions continue to grow, and where the increase in global temperature of 2.6 °C to 4.8 °C by 2100, the concentration of methylmercury will increase by 10 percent for the king salmon. In the best scenario, with low emissions and a global temperature increase of 0.3 to 1.7 °C by the end of the century, the mercury levels did rise as a percent.

For forage fish, such as Pacific sardines, anchovy, and Pacific herring, a species that have a ecological role and a key business in the ecosystem of the Pacific coast, the rise of methylmercury is expected to be 14% in the case of high emissions, and 3 % with low emissions. These are changes in the diet and the composition of the food chain due to warming of the oceans that are the cause.

Fish at the beginning of the food chain

In the course of the last century, stocks of Atlantic cod have been overfished along the north-east coast of Canada.In the north-east of the Pacific ocean, the natural factors and environmental stressors, such as predation, loss of habitat, warming of oceans and fisheries, causing a decline in salmon stocks royal. The combination of these pressures makes the Pacific salmon more susceptible to bioaccumulation of methylmercury.

When a species is overfished, the fishing fleets are expanding, and adjust their targets, opting often for the base of the food chain. Cascading effects lead to changes in the composition of the food web of other species, which may result in the transfer of contaminants such as persistent organic pollutants and methyl mercury to top predators.

When fish are removed from the food chain, large predators may be forced to consume more prey or prey different, or smaller fish than they do usually, and become highly contaminated with mercury.

The combination of climate change, and overfishing is transforming the population of fish in the ocean and their geographic distribution. This also modifies their exposure to pollutants, e.g. by increasing the levels of methylmercury in atlantic cod and Atlantic bluefin tuna, the fish that are often consumed by humans.

Protect the health and the planet

In the light of these data, the sector of public health should review the recommendations regarding fish consumption for the people most likely to be exposed to mercury (coastal communities) or suffer the negative effects (pregnant women, infants and children).

Our simulations show that the concentrations projected from methylmercury in fish-fodder, and the king salmon will exceed the limits on canadian consumption of mercury in the course of the century, as well as the level recommended by the world health Organization.

In our world dominated by the human being, it is imperative that we consume fish and shellfish from sustainable fisheries and that we make every effort to reduce the pollution of the oceans. Environmental policies-national and international, such as the sustainable development Goals of the united Nations for the conservation and sustainable exploitation of the oceans, seas and marine resources (SDO 14) and the Paris Agreement on climate, can be used to protect marine species and protect our blue planet for generations to come.

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This text first appeared on the site of the franco-canadian of The Conversation. Reproduced with permission.

“The science in her words” is a forum where scientists of all disciplines can take the floor, either in open letters, or excerpts from books.

Les changements climatiques et la surpêche font augmenter le niveau de mercure dans le poisson

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