EFFECTS OF SUCTION DREDGING ON STREAMS - A REVIEW AND AN EVALUATION STRATEGY

Suction dredging for gold in river channels is a small-scale mining pr actice whereby streambed material is sucked up a pipe, passed over a s luice box to sort out the gold, and discarded as tailings over another area of bed. Natural resource managers should be concerned about suct ion dredging because it is common in streams in western North America that contain populations of sensitive aquatic species. It also is subj ect to both state and federal regulations, and has provided the basis for litigation. The scientific literature contains few peer-reviewed s tudies of the effects of dredging, but knowledge of dredging practices , and the biology and physics of streams suggests a variety of mechani sms linking dredging to aquatic resources. Effects of dredging commonl y appear to be minor and local, but natural resource professionals sho uld expect effects to vary widely among stream systems and reaches wit hin systems. Fishery managers should be especially concerned when dred ging coincides with the incubation of embryos in stream gravels or pre cedes spawning runs soon followed by high flows. We recommend that man agers carefully analyze each watershed so regulations can be tailored to particular issues and effects. Such analyses are part of a strategy to (1) evaluate interactions between suction dredging and other activ ities and resources; (2) use this information to regulate dredging and other activities; (3) monitor implementation of regulations and on- a nd off-site effects of dredging; and (4) adapt management strategies a nd regulations according to new information. Given the current level o f uncertainty about the effects of dredging, where threatened or endan gered aquatic species inhabit dredged areas, fisheries managers would be prudent to suspect that dredging is harmful to aquatic resources.