The purpose of this work was to investigate potential effects of brook stickleback (Culaea inconstans) on aquatic communities in eastern Washington. Brook stickleback, which are indigenous to drainages east of the continental divide and central North America, have on five occasions, been documented within drainages on the western slope of the Rocky Mountains. Since 1999 brook stickleback have repeatedly been observed within creeks and ponds of the Rock Creek Drainage, which is a tributary of the Palouse River, and ultimately, the lower Snake River, Washington. Included within their newly adopted eastern Washington distribution are several lotic and lentic environments within the Turnbull National Wildlife Refuge (TNWR) which poses potential complications for waterfowl management due to diet overlap. We used a combination of stock tank experiments, 24 hour feeding trials, waterfowl counts, and a comparison of carbon and nitrogen stable isotope signatures of stickleback versus mallard ducks (Anas platyrhynchos) from both stickleback-infested and stickleback-absent wetlands to investigate stickleback effects.
Results/Conclusions
A replicated 350 l stock tank experiment suggests brook stickleback have a limited impact on the macroinvertebrate constituents of the TNWR pond communities. Of nine taxa included within the study, significant negative stickleback effects were only observed for Annelida, Diptera (Chaoborus), and Zygoptera. However, stock tank experiments designed to detect stickleback effects on the zooplankton suggest large-bodied and heavily pigmented species are negatively impacted by stickleback. Significant negative stickleback effects were detected on total zooplankton biomass and abundance as well as these same measures for the branchiopods Daphnia and Lynceus, and the calanoid copepod Diaptomus. Twenty-four hour electivity trials illustrate stickleback exhibit a positive preference for branchiopods, are neutral in their preference for Diaptomus, and actively avoid ingesting small bodied and relatively transparent cyclopoid copepods. Comparisons of waterfowl abundance among fish-free versus fish-present ponds suggests the abundance of waterfowl is lower in ponds possessing fishes. Further, although we observed no difference in stable nitrogen isotope signatures of young-of-the-year waterfowl inhabiting stickleback-present versus stickleback-absent ponds, these same individuals possessed significantly lower stable carbon isotope signatures indicative of a more pelagic diet.