Biologists determined that short-term, seasonal exposure to pesticides in rivers and basins may limit the growth and size of wild salmon populations. In addition to the widespread deterioration of salmon habitats, these findings suggest that exposure to commonly used pesticides may further inhibit the recovery of threatened or endangered populations.
"Major efforts are currently underway to restore Pacific salmon habitats in an effort to recover depressed populations," says David Baldwin of the National Oceanic and Atmospheric Administration (NOAA), who co-authored the study with NOAA colleagues in the December issue of the ESA journal Ecological Applications. "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.
Pesticides include insecticides, herbicides and fungicides that are usually applied to agricultural and urban landscapes. They primarily enter waterways in spray drift, surface runoff and irrigation return flows.
"An important aim of the work was to link known sublethal effects for individual salmon to impacts on the productivity of salmon populations," explains 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
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Ecological Society of America