John Wiley & Sons, Ltd.

Growth and survival of pacific coho salmon smolts exposed as juveniles to pesticides within urban streams in western Washington

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Pesticides are frequently detected in urban streams with concentrations often exceeding those reported in surface waters within agricultural areas. We studied growth, survival, and return rates of coho salmon (Oncorhynchus kisutch) smolts exposed to a pesticide mixture (“cocktail”) representative of that most frequently reported within urban streams in western Washington State, USA, in fall through early spring. Smolts were either continuously exposed to pulses of the cocktail from fertilization through swim‐up (2007–08) or fertilization through smoltification (2007–08 and 2008–09), coded wire tagged, and released in 2008 and 2009. Pre‐release endpoints (growth [condition factor], survival, gender, brain acetylcholinesterase (AChE) activity, and gonado‐ and hepatosomatic indices) were not affected. However, the number of returning adults exposed to the cocktail to swim‐up (0.90%, n = 42) was more than twice that of unexposed controls (0.38%, n = 26) in 2008, whereas in 2009, fish exposed through smoltification returned in lower numbers (0.15%, n = 18) than controls (0.37%, n = 30). Variability in return rates among treatments between years was comparable to that observed in previous whole life cycle studies with Pacific salmon and other contaminants. Results suggest exposure to pesticides in urban streams does not directly impair early life stages of coho salmon, and that additional studies incorporating releases of larger numbers of smolts across several years are necessary to adequately quantify effects on return rates. Environ Toxicol Chem © 2014 SETAC

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