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Low Levels of Pesticides Slow Wild Salmon Population Recovery

(Beyond Pesticides, December 18, 2009) Biologists are finding that short-term, seasonal exposure to pesticides in rivers and basins limit the growth and size of wild salmon populations. Along with the widespread deterioration of salmon habitats, these findings show that exposure to commonly used pesticides continue to detriment the recovery of the salmons’ populations. The findings can be found in the study, “A fish of many scales: extrapolating sublethal pesticide exposures to the productivity of wild salmon populations,” in the December 2009 issue of the Ecological Society of America (ESA) journal, Ecological Applications.

“Major efforts are currently underway to restore Pacific salmon habitats in an effort to recover depressed populations,” says David Baldwin, Ph.D., of the National Oceanic and Atmospheric Administration (NOAA), who co-authored the study with NOAA colleagues, “However, not much research has been done to determine the importance of pollution as a limiting factor of ESA-listed species.”

The researchers studied the impact of pesticides, such as diazinon and malathion, on individual salmon using pre-existing data, and then devised a model to calculate the productivity and growth rate of the population. They used several exposure scenarios to reflect realistic pesticide use across various landscapes and over time.

“An important aim of the work was to link known sublethal effects for individual salmon to impacts on the productivity of salmon populations,” explains Dr. Baldwin.

The biologists found in previous studies that, on an individual level, the pesticides directly affected the activity of acetylcholinesterase, an important enzyme in the salmon brain. As a result, the salmon experienced reductions in feeding behavior. The reductions in food were then extended using the model to calculate reductions in the growth, size, and subsequent survival at ocean migration. In one scenario, the model predicted that, within a span of 20 years, returning spawners would have an increase of 68 percent abundance compared to a 523 percent projected increase in an unexposed chinook population.

“The model showed that a pesticide exposure lasting only four days can change the freshwater growth and, by extension, the subsequent survival of subyearling animals,” says Dr. Baldwin. “In addition, the seasonal transport of pesticides to salmon habitats over successive years might slow the recovery of depressed populations.”

The researchers conclude that improving water quality conditions by reducing common pollutants could potentially increase the rate of recovery. Looking to the bigger picture, “This should help resource managers consider pesticides at the same biological scale as physical and biological stressors when prioritizing habitat restoration activities,” says Dr. Baldwin.

In September, The National Marine Fisheries Service (NMFS) determined that accepted uses of chlorpyrifos, diazinon and malathion are likely to jeopardize the continued existence of 27 species of endangered or threatened salmon and steelhead. NMFS found that current uses were likely reducing the number of salmon returning to spawn.

Background on Diazinon

• Contaminates rivers throughout the west at levels harmful to fish or their food sources according to the U.S. Geological Survey. The basins where diazinon was detected at harmful levels include the Willamette, San Joaquin, Tulare, the Central Columbia Basin and Puget Sound. It was also detected in King County, Washington streams.
• Impairs feeding, predator avoidance, spawning, homing and migration capabilities by impeding salmon sense of smell.
• Leads to weakened swimming activity in juvenile trout.
• Is acutely toxic to salmon food sources.

Background on Malathion

• Contaminates rivers throughout the west at levels harmful to fish or their food sources according to the U.S. Geological Survey. The basins where malathion was detected at harmful levels include the Willamette, San Joaquin, Tulare, and the Central Columbia Basin. It was also detected in King County, Washington streams.
• Leads to weakened swimming activity in juvenile trout.

Previous Daily News Coverage

Federal Agency Releases Plan to Protect Salmon from Pesticides, November 21, 2008
Three Additional Pesticides Found to Harm Salmon, April 30, 2009
Take Action: Tell EPA to Protect Endangered Salmon from Toxic Pesticides, May 19, 2009

Soucre: ScienceDaily Press Release


One Response to “Low Levels of Pesticides Slow Wild Salmon Population Recovery”

  1. 1
    Richard Cornett Says:

    It appears that the buffer zones required for pesticide applications under this opinion will be applied essentially to every ditch, drain, canal and irrigation furrow that could potentially drain from an agricultural field into salmon habitat, and because these small waterways are omnipresent, and western specialty crop fields are relatively small, EPA’s implementation plan looks like a virtual prohibition of use in large agricultural areas of California, Washington, Oregon and Idaho.

    With 34 more pesticides to be reevaluated in the upcoming biological opinions pursuant to the settlement,the actions now being taken are setting precedents for all of these decisions on restrictions of these additional pesticides yet to come. The evaluation is taking place without consultation with agriculture or any assessment of its economic impact.
    The EPA has given little rationale for planning to impose these inflexible restrictions on a hasty, litigation-driven schedule that does not allow growers to adapt. If you would like to read more about the scientific facts about the benefits of crop protection tooks, visit http://www.healthyplants.org and leave a comment on my blog site.

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