Freshwater mussels (Unionacea: bivalvia) are important components of many aquatic ecosystems. Unfortunately, many mussel species are imperilled. Seventy of about 300 species are listed as threatened or endangered under the Endangered Species Act of 1973 and another 143 species are afforded some level of protection. Of the seven known native species of mussels in the Pacific Northwest, only one, the California floater (Anodonta californiensis), is currently a federal species of concern. However, little information is available describing the status of freshwater mussels or the effects of possible threats to their persistence, but over-harvest, altered water quantity and quality, land use, introduced species, and physical disturbance have been cited as likely causes
Suction dredge placer mining is an increasingly frequent activity that may affect the survival of mussels, however, the effect of suction dredge mining on freshwater mussels has received little attention. We quantified the effects of being entrained, exposed, and/or buried by suction dredge placer mining on the short-term survival of western ridged mussels (Gonidea angulata) and western pearlshell mussels (Margaritifera falcata) in the Similkameen River, Washington.
The primary experimental treatments were entrainment by a suction dredge versus non-entrainment. The secondary experimental treatments were exposure and burial. No obvious physical damage to mussels was observed due to entrainment by the suction dredge and entrainment had no effect on the survival of mussels. All exposed mussels survived the 6-week experiment. However, burial by dredge tailings resulted in the death of a substantial percentage of mussels of each species and no mussels were able to excavate from experimental dredge tailings. Our results have significant conservation implications and emphasize the need for additional research.
We thank the many people who contributed their time and effort to this project. We especially appreciate the work of J. Franklin, J. Cain, and M. Erickson who volunteered their time, equipment, and prospecting experience and L. Allemandi, D. Dagnon, R. Barthol, H. Cervaux and M. Cervaux for providing access to the Similkameen River.
J. Anderson, M. Cookson, J. Fleckenstein, C. Hayes, M. Hayes, L. Hofmann, C. Iten, T. Jackson, C. Olds, D. Papa, C. Parsons, and M. Skrilitz helped conduct the experiment on the Similkameen River.
J. Konovsky helped select the study site on Mill Creek and D. Swedberg arranged housing for fieldwork. C. Preston provided timely assistance with permitting. L. Zimmerman, S. Hanlon and W. Henley provided valuable information and suggestions regarding the design of the study.