(Beyond pesticides, June 3, 2021) A report published in Royal Society Open Science finds parasitic lice resistant to pesticides (Lepeophtheirus salmonis) endanger wild and farmed fish populations in the North Atlantic. The intensive use of pesticides to kill the parasite has led to widespread resistance to multiple pesticides, which has resulted in increased rates of infection among North Atlantic salmon populations. Overexploitation of wild fish and other ocean organisms has depleted seafood stocks globally. Some fisheries commercialize aquaculture practices, such as fish / seafood farming, as a solution to overfishing. However, the aquaculture industry repeatedly faces sustainability issues and fails to comply with environmental regulations that threaten marine health.
The oceans are essential to human health and well-being, feeding billions of people, supporting millions of jobs and providing medicinal materials. However, environmental contaminants like pesticides have a profound impact on the ecosystem and the inhabitants. Therefore, there is a need to understand how pesticides can influence the resistance of populations of deadly pests, especially in ecologically vulnerable and highly interconnected ecosystems such as ocean basins. The report’s authors caution: “These findings demonstrate the speed at which this parasite can develop widespread multi-resistance, illustrating why the aquaculture industry has repeatedly lost the arms race with this very problematic pest. “
During the past two decades, organophosphate and pyrethroid insecticides have been the two main chemical classes used to control parasitic salmon lice. However, laboratory studies reveal increasing resistance of salmon lice to these chemicals, in addition to multi-resistance after in vitro crossing. Since laboratory studies identify that multi-resistance to the two chemical classes can occur through crossbreeding, the researchers suggest that this same resistance manifests itself in the field. Therefore, this study aims to address multi-resistance in salmon lice populations resulting from reduced susceptibility to multiple chemicals in the North Atlantic region.
From 2000 to 2017, researchers sampled 1,988 lice from wild salmonid populations in the Northeast Atlantic (salmon, sea trout and farmed salmon). The researchers analyzed the parasites for genetic markers for resistance to pyrethroids and organophosphates.
The results of the study reveal that genetic resistance in salmon lice has an evolutionary spatiotemporal pattern (place and time). This pattern means that lice show simultaneous resistance to organophosphate and pyrethroid insecticides throughout the North Atlantic except Canada. Over 50 percent of lice populations around fish farms are resistant to both classes of insecticides. Some sample areas contain populations of lice which are all resistant to at least one pesticide. The researchers conclude that areas with a high aquaculture intensity, using a large amount of chemicals for delousing, result in multidrug resistance to pesticides among populations of salmon lice.
The United States Department of Agriculture (USDA) defines aquaculture as any “farming of aquatic organisms, including baitfish, crustaceans, food fish, molluscs, ornamental fish, sport or game fish and other aquaculture products”. Farmed fish, like Atlantic salmon, in this case, use one of the riskiest aquaculture practices, open net pens in both coastal and offshore regions. These enclosures allow easy exchange of waste (i.e. droppings), chemicals (e.g. pesticides and pharmaceuticals), pests / diseases (e.g. sea lice) between the farm and the surrounding ocean environment. The release of wastes, chemicals and pests / diseases can have a disastrous impact on marine organisms and plants, disrupting ecosystem services. Many of these enclosures are in relatively remote areas, somewhat “hidden” from public scrutiny. However, these fish live in very crowded conditions, unlike wild fish. Fish consume foods that may contain various pharmaceuticals or insecticides to control diseases and pest infestations that commonly occur under these conditions. Additionally, farm enclosures can attract predators, such as marine mammals, which can become entangled and drown in fish farm nets.
This study is one of the first to demonstrate spatiotemporal resistance to multiple chemical pesticides in salmon lice under real conditions. According to the results, years of specific sampling in combination with geography highlight how resistance spreads. Under normal conditions, lice populations decline in winter with a change in the dispersal of salmonid populations. However, the crowded and over-processed nature of on-farm fishing creates an environment in which these parasites persist during regular winter diebacks. Resistant lice appear in farm pens a few years after treatment and leak by current through the barrier due to their small size. All the oceans connect to each other, circulating nutrients, chemicals, and organisms around the world. Therefore, pesticide resistant lice have the potential to spread their resistance gene throughout the ocean basin. These mutant pests have already made their way from Scandinavia to Greenland and Iceland, where farmers have never used chemical pesticides.
There are similar reports of the harmful effects of farmed fish on the west coast of Scotland and the Northern Isles. The use of antibiotics and pesticides on local marine ecosystems (i.e. insecticides to control sea lice in farmed salmon) results in coastal habitat loss and genetic risks and health for wild marine populations. The biodiversity of marine species is already declining rapidly due to overfishing, global warming, pathogens and pollution. This loss of biodiversity can lead to changes in the function of marine and terrestrial ecosystems and reduce ecosystem services.
Salmon lice represent the greatest challenge for aquaculture production and environmentally sustainable aquaculture. These parasites attach themselves to the fish’s skin and feed on its blood and mucus, creating sores that lead to infection or death. It is therefore essential to study the ubiquity and distribution of multidrug resistance to pesticides among sea lice populations in the North Atlantic. Pesticides are ubiquitous in all aquatic ecosystems, from rivers, lakes and oceans to Arctic glaciers. Therefore, it is essential to understand how pests can develop resistance to pesticides used to control populations in order to protect human, animal and environmental health.
Advocates say the federal government should require safeguards in aquaculture industry practices to avoid harmful impacts on wild marine organisms, water resources and aquatic habitats. A sustainable aquaculture sector, according to the Seafood Watch program of the Monterey Bay Aquarium, require robust and timely production data, prohibit the discharge of wastes beyond certain levels determined by the environment, and specify appropriate locations for such operations. Instead, federal policy opted, as the Center for American Progress said, to “focus on weakening effective fisheries management measures and selling federal waters to big business with little guarantees.”
The regulation and disposal of pesticides, not only in aquaculture but in agriculture and other areas of use, can reduce the spread of harmful effects on wildlife, ecosystem and health. In addition, the melting glaciers associated with the climate crisis are raising new concerns about the high levels of chemical concentrations in the oceans from pesticides trapped in the ice. The use of toxic pesticides must stop to protect the waterways of the country and the world and reduce the number of resistant pesticides and parasites in our food, water and wildlife resources. Learn more about the dangers of pesticides to wildlife and what you can do through the Beyond Pesticides Wildlife Program page.
There are many resources that individuals can use to acquire knowledge and apply practices to avoid the use of pesticides and its harmful effects. These include news stories, local organizations, policies on pesticides in schools, regulatory contacts and less toxic pest control operators. Organic practices can successfully eliminate the use of toxic pesticides. Replacing pesticides with organic and non-toxic alternatives is crucial to protect public health and ecosystems from the toxicity of pesticides. Buying, growing and supporting organic can help eliminate the heavy use of pesticides in the environment and in your diet. For more information on why organic is the right choice for consumers and the farm workers who grow our food, see the Beyond Pesticides, Health Benefits of Organic Agriculture webpage.
Help Beyond Pesticides educate and build the movement that will provide long-needed protection for humans, animals and the entire environment by participating in the National Pesticides Forum on June 8-15. Growing Healthy Communities brings together expert scientists, farmers, policy makers and activists to discuss strategies to eliminate the harms of using toxic chemicals in favor of non-toxic organic solutions. The conference began with a pre-conference on May 24, launched on May 25, and continues every Tuesday through June 15, 2021. Registration is open today and available through the web page at this link. It starts with us. When you register, you will be able to see presentations from the entire conference.
All positions and opinions not attributed in this article are those of Beyond Pesticides.