Effects of a Small Suction Dredge on Fishes and Aquatic Invertebrates in Idaho Streams

Abstract

Abstract A typical dredge (intake diameter 7.6 cm) was operated on four small Idaho streams during July-September 1980 to evaluate some of the effects on aquatic organisms that may result from the use of small suction gold-dredges. Mortality of eggs, sac fry, and fingerlings of several species of trout was monitored, as was that of benthic invertebrates that were entrained through the dredge. The ability of invertebrates to recolonize a dredged area was assessed, and the performance of the dredge was evaluated. Un-eyed cutthroat trout (Salmo clarki) eggs experienced 100% mortality within 1 hour after entrainment. Eyed cutthroat trout eggs showed means of 29% and 35% for 1-hour and 36-hour mortalities, respectively. The 19% mortality of eyed eggs of hatchery rainbow trout (Salmo gairdneri) after 10 days was similar to that of the control group. Hatchery rainbow trout sac fry experienced 83% mortality after 20 days as compared with 9% for the controls. Yolk sacs were detached from approximately 40% of the f...