T4 PM Endangered Species and Environmental Contaminants: Status of the Science (Part 2)
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in Ballroom 4

(DAV-1117-836850) Correlating the sublethal neurotoxicty of carbaryl with behavioral impairments in salmonids.

Davis, J¹, Labenia, J², Baldwin, D², French, B², Scholz, N², ¹ U.S. FWS - Western Washington Fish & Wildlife Office, Lacey, WA, USA² NOAA Fisheries - Northwest Fisheries Science Center, Seattle, WA, USA

ABSTRACT- Foraging habitat of coastal cutthroat trout, which inhabit Willapa Bay, Washington, is periodically contaminated with carbaryl. Salmonids, such as cutthroat trout, forage throughout the estuary in the summer months when carbaryl, a carbamate insecticide, is applied to oyster beds at low tide to control burrowing shrimp populations. Previously proposed for listing under the Endangered Species Act, this population of coastal cutthroat trout is potentially exposed to sublethal concentrations of carbaryl that is transported off-site from oyster beds via tidal activity. On the day of spray, carbaryl has been measured in the estuarine water column at concentrations >1,000 ppb. Previous studies determined cutthroat trout do not show an olfactory response to carbaryl, do not avoid carbaryl-containing water, and that short-term carbaryl exposure rapidly (<2 hrs) depresses brain and muscle acetylcholinesterase activity in a dose-dependent manner (IC₅₀s of 213 ppb and 185 ppb, respectively) for approximately two days. Sublethal, neurotoxicity bioassays with behavioral assessment endpoints were utilized to determine the impacts of environmentally relevant carbaryl concentrations on the swimming behavior of cutthroat trout as well as their vulnerability to predation. Results indicate salmonids' swimming performance and ability to avoid predation are significantly affected at carbaryl concentrations ≥750 ppb and ≥500 ppb, respectively. Therefore, carbaryl applications in the estuary may impair the behavioral performance of exposed cutthroat trout and increase their vulnerability to predators.

Key words: carbaryl, salmonids, acetylcholinesterase inhibition, neurobehavioral effects