Oysters, crabs, and burrowing shrimp: Review of an environmental conflict over aquatic resources and pesticide use in Washington State's (USA) coastal estuaries

Washington State's coastal estuaries are productive shallow water environme nts that support commercial fisheries for Dungeness crabs (Cancer magister) and English sole (Parophrys vetulus) by providing 0+ (settlement to age 1) populations with critical refuge and foraging habitats until subadults mig rate to the nearshore coast. Intertidal mudflats also constitute prime area s for commercial oyster (Crassoscrea gigas) culture, an important industry for the coastal communities of Willapa Bay and Grays Harbor that supply muc h of the nation's oysters. Conflicts over natural resources and estuarine u tilization have arisen over the last 37 yr due to the use of carbaryl (an o rganocarbamate pesticide) by oyster growers on their grounds to control pop ulations of burrowing thalassinidean shrimp (Neotrypaea californiensis and Upogebia pugettensis). Burrowing shrimp, which have an indirect negative ef fect on oyster survival and growth through bioturbation and sediment destab ilization, are killed by carbaryl, as are 0+ and subadult Dungeness crabs, 0+ English sole, and other non-target species present on the tideflats at t he time of application. The pesticide is delivered at 9 kg ha(-1) directly to the mudflat as a wetable powder during low tides in July and August. Com mercial crabbers and other groups who have economic, recreational, and envi ronmental interests in the estuaries have generally opposed use of the chem ical that oyster growers maintain is essential to sustain production levels . For years, government natural resource agencies that regulate the use of carbaryl lacked critical information needed to effectively manage the progr am. An Environmental impact Statement (EIS) and Supplemental EIS have provi ded much of that data and helped shape management decisions with regard to establishing carbaryl concentration rates and total allowable spray area. A dditional research is needed to develop more economically and environmental ly sound policies for shrimp control based on burrowing shrimp-oyster inter actions on an estuarine-wide scale. In this paper we review issues pertaini ng to oyster culture, the use of carbaryl to control burrowing shrimp popul ations, and effects on non-target species, drawing upon research from publi shed articles as well as unpublished data collected by the authors. We also discuss what is known of burrowing shrimp life history and ecology and emp hasize the importance of integrating information on shrimp, such as timing of recruitment, variability in year class strength, and patterns of habitat use, into carbaryl control policies or alternative strategies that may be developed in the future. We recommend controlled experimentation be done to examine the ecological effects of delaying carbaryl application to some gh ost shrimp beds until October after peak recruitment of 0+ ghost shrimp has occurred, allowing the number of hectares treated each year to vary based on fluctuations in pest population densities, and modifying the substrate b y applying a dense layer of oyster shell to the mudflat (shell pavement) to reduce recruitment of ghost shrimp.