Brian Barton
Salmon face a variety of threats during their life cycle, many of which are caused by human activity. Water pollution is a significant cause of the decline in salmon populations, with urban stormwater runoff carrying pollutants, toxins, and chemicals from roads and other developed areas into the freshwater streams and rivers where salmon spawn. This pollution can directly poison salmon, making it difficult for them to breathe and reducing their chances of survival. In addition, salmon accumulate toxic chemicals as they grow, which can reduce their growth, increase their susceptibility to disease, and alter their hormone production. Climate change, invasive species, habitat degradation, and over-exploitation further compound the challenges facing salmon populations.
| Characteristics | Values |
|---|---|
| Toxic chemical pollution | PCBs (polychlorinated biphenyls), PBDEs (polybrominated diphenyl ethers), 6PPD-quinone, pesticides, flame retardants |
| Impact of toxic chemicals | Reduced growth, increased disease susceptibility, altered hormone production, increased health risks for predators including humans |
| Sources of toxic chemicals | Stormwater runoff, industrial runoff and erosion from agriculture and logging, vehicle emissions |
| Other types of pollution | Eutrophication of aquatic habitats, climate change, invasive species, habitat degradation |
| Impact of other types of pollution | Reduced access to important habitats, changes in water temperature and habitat quality, increased competition, predation and disease |
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What You'll Learn
Stormwater runoff
A study found that coho salmon nearly died within hours of exposure to stormwater runoff. The heavy metals and toxins in the stormwater poison the fish, making it difficult for them to breathe. The high numbers of coho salmon that die near urban centers indicate the high levels of human pollution in the area.
Another study identified 6PPD-quinone, a chemical produced by the wear of car tires, as the cause of high rates of coho salmon deaths in the streams of developed areas in Puget Sound before they can spawn.
In addition to heavy metals and toxins, stormwater runoff can also contain harmful chemicals such as pesticides and flame retardants, as well as sediment from construction sites. This sediment can clog and abrade salmon gills and smother their eggs, leading to disruptions in the fishing industry.
To minimize the impact of stormwater runoff on salmon populations, it is important to reduce the amount of impervious surface cover in urban areas and implement erosion control measures such as silt fences and organic matting to protect soil from being washed away.
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Urban pollution
Urban roads are another contributor to the problem. Roads collect contaminants from various sources, such as tires, brake pads, car washes, vehicle exhaust, and road salts. During storms, these contaminants can be washed into salmon-bearing streams, posing a lethal danger to the fish. One specific chemical, 6PPD-quinone, a preservative found in tires, has been identified as the cause of high mortality rates among coho salmon in urban streams. This chemical is formed when 6PPD oxidizes upon exposure to ozone and has been linked to "urban runoff mortality syndrome" in certain fish species.
The accumulation of toxic chemicals in urban waterways also poses a significant risk to salmon. As salmon grow, they accumulate these chemicals, such as PCBs (polychlorinated biphenyls) and PBDEs (polybrominated diphenyl ethers). These contaminants can reduce growth, increase disease susceptibility, and alter hormone production, ultimately lowering the survival rate of the salmon. Furthermore, as predators, including humans, consume contaminated salmon, the health risks of these toxic chemicals are magnified.
The impact of urban pollution on salmon populations is a pressing issue that requires attention and action. Strategies to address this problem include monitoring waterways for specific contaminants, such as the work done by the British Columbia Conservation Foundation (BCCF) and their partners in detecting 6PPD-quinone. Additionally, organizations like the Pacific Salmon Foundation (PSF) are studying the effects of road salts on the salmon food web to raise awareness and develop mitigation strategies. These collective efforts aim to reduce the harmful effects of urban pollution on salmon and, by extension, the ecosystems and communities that depend on them.
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Climate change
Water Temperature Rise
Rising air temperatures lead to warmer water in lakes, rivers, and streams. Water temperatures above 64 degrees Fahrenheit stress salmon, and temperatures exceeding 70 degrees Fahrenheit can be fatal. Warmer water also has lower oxygen levels and fewer nutrients, creating conditions that are less conducive to salmon survival. Salmon require cold, oxygen-rich water to thrive, and the increase in water temperature jeopardizes their health and existence.
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Ocean Acidification
Human activities have contributed to increased carbon dioxide levels in the atmosphere and oceans. The excess carbon dioxide forms carbonic acid in the ocean, leading to a 30% increase in average ocean acidity since the Industrial Revolution. This heightened acidity damages the plankton and crustaceans that salmon depend on for food, disrupting the food chain and negatively impacting salmon populations.
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Habitat Degradation
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Habitat degradation
Salmon require specific habitats to survive and thrive. These habitats are being degraded by human activity and climate change, threatening the survival of salmon.
One of the primary ways in which pollution harms salmon is through the degradation of their habitat. Salmon require cool, clean water with diverse estuaries and rivers with ample food to survive and reproduce. Human activities such as residential, commercial, and industrial development can displace or destroy salmon habitats. For example, Puget Sound has lost habitat function across one-third of its 2,500 miles of shoreline due to armoring. This has resulted in the loss or extensive modification of 50-90% of the land along waterways in Washington, impacting the riparian zones and floodplains that are critical for aquatic species like salmon.
In addition to direct habitat loss, pollution can also degrade salmon habitats by reducing water quality. Contaminants from agricultural runoff, logging, and other industrial activities can pollute waterways, making the water unsafe for salmon. For example, an EPA study found high levels of chemicals in carp from the Columbia River, and over 92 different contaminants were detected in the fish that are consumed by tribal populations. These toxic chemicals, such as PCBs and PBDEs, can accumulate in salmon as they grow, reducing their growth, increasing their susceptibility to diseases, and altering their hormone production, ultimately reducing their survival rates.
Climate change further exacerbates the problem by causing warmer water temperatures, which have lower nutrient levels and oxygen content, creating conditions that are less beneficial for salmon. Warmer water also favors the growth of sub-tropical zooplankton, which is poor food for juvenile salmon, making it harder for them to survive. As temperatures continue to rise, glaciers that provide cold water to streams in the Pacific Northwest are vanishing, and mountain snowpacks are becoming smaller, leading to lower water levels in streams during the summer when young salmon are at a critical life stage.
The combination of human activities and climate change can create extreme environments that further degrade salmon habitats. For example, increased rainfall can lead to more frequent flooding events, which can destroy salmon nests (redds), reduce habitat complexity, and flush young salmon out of their calm-water habitats, reducing their chances of survival. In addition, landscapes altered by major wildfires can be more severely impacted by climate change, leading to further habitat degradation for salmon.
To preserve salmon populations, it is essential to address the degradation of their habitats. This includes implementing regulations to protect and restore riparian lands, enforcing consistent standards for habitat conservation, and mitigating the impacts of climate change on water temperatures and water levels. By taking action to preserve and restore salmon habitats, we can help ensure the continued existence of these important species.
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Parasites and diseases
Salmon are susceptible to a wide range of parasites and diseases, which are made more prevalent and intense by pollution.
Parasites
Salmon are affected by a variety of parasites, including sea lice, Argulus species, Gyrodactylus, Henneguya salminicola, and Myxobolus cerebralis. Sea lice are a particular problem, as they can spread from farmed salmon to wild salmon, threatening wild populations. The Henneguya parasite has a complex life cycle, with the salmon acting as one of two hosts. The parasite is released when the fish spawns, infecting juvenile salmon as they migrate to the ocean. While Henneguya does not appear to cause significant harm to the host salmon, it does impact the economic viability of salmon farming. Salmon are also susceptible to endoparasites such as myxozoons, microsporans, and haematozoons, which proliferate within their hosts. Pollution can increase the prevalence and intensity of parasitism in salmon populations, favouring the survival and reproduction of intermediate hosts. For example, studies have shown that exposure to pollutants increases the number of ectoparasites on the gills of fish.
Diseases
Salmon are also vulnerable to various diseases, such as enteric redmouth disease, a bacterial infection characterised by subcutaneous hemorrhaging of the mouth, fins, and eyes, and piscirickettsiosis, which has a high mortality rate. Ulcerative dermal necrosis (UDN) was a major cause of disease and death in adult salmon returning to freshwater to spawn in the 1970s and 1980s, although the cause is still unclear. Chronic exposure to pollutants can impair the immune response of salmon, making them more susceptible to diseases and parasites.
Farmed salmon are particularly prone to disease due to overcrowding and poor water quality. To prevent mass die-offs, fish farmers often use antibiotics, which can contribute to antibiotic resistance in humans.
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Frequently asked questions
Salmon are harmed by pollution in multiple ways. Stormwater runoff from urban areas carries pollutants and chemicals, such as heavy metals and toxins, into streams and rivers where salmon spawn, causing them to die prematurely. Salmon are also affected by toxic chemical pollution, such as PCBs and PBDEs, which can accumulate in their bodies as they grow, reducing growth, increasing disease susceptibility, and altering hormone production.
There are various sources of water pollution that harm salmon. Increased urbanization and development contribute to more polluted runoff, with roads collecting contaminants from tires, brake pads, car washes, vehicle exhaust, and road salts. Agricultural and logging activities also contribute to water pollution through runoff and erosion. In addition, certain chemicals used in tires and brake pads can be particularly toxic to salmon, such as 6PPD-quinone, which causes "urban runoff mortality syndrome" in some fish species, especially coho salmon.
Water pollution has been a major cause of the decline in stocks of Atlantic salmon, affecting all life stages of the fish. It also impacts the habitats of salmon, making their migration more challenging. Pollution can also contaminate the salmon that are consumed by humans, leading to potential health risks. For example, tribal populations that rely heavily on salmon as a food source have detected more than 92 different contaminants in the fish, with some at levels harmful to human health.
