Suction Dredge Mining Impacts on Pacific Lamprey Populations and Habitat in Washington State: A Case Study of the Entiat River

Suction dredge mining is a largely unregulated recreational activity in Washington State with potentially significant impacts to aquatic habitat. Although dredging has the potential to cause widespread ecological effects, only impacts to select species have been thoroughly assessed. Due to their reliance on freshwater habitat throughout multiple life stages, Pacific lamprey are significantly vulnerable to impacts from dredging practices. This thesis focuses on assessing the effects of dredging to lamprey habitat within state-owned aquatic lands of Washington. Pacific lamprey are anadromous, utilizing freshwater habitat throughout key life stages including spawning in substrate ranging from coarse gravel to fine sand, and burrowing into streambeds as larvae to grow for a maximum of seven years (Pirtle et al., 2003; Graham and Brun, 2006). By conducting a controlled dredging experiment along the Entiat River and comparing alterations to water quality and stream morphology before and immediately after dredging, two months later, and at the beginning of the following season, changes to habitat were quantified. When water quality was assessed, no significant impact to parameter levels were observed. Although changes to overall grainsize proportions were small, distributions showed coarser material directly at dredged sites, while finer material increased downstream. Channel profiles showed reductions in material following dredging, as well as minimal recovery two months after the activity and at the beginning of the following season. Artificially created tailings piles were observed to experience a 55.40% reduction in material volume over two months, while total hole volume showed a contrasting increase of 8.10%. Additionally, tailings experienced a 100% reduction in volume 11 months following dredging activity while dredge holes were reduced by 9.6%. Results can be related to habitat preferences of other aquatic species to determine ecosystem-wide impacts as well as providing necessary data to extrapolate impacts to similar systems throughout the state. Using these results, I provided recommendations to apply throughout management decisions and developed further recommendations for research