Sedimentation rates in brown trout (Salmo trutta) spawning reaches in the Styx River
Craig H. Dolphin
Email: CraigDolphin@yahoo.com
Abstract
Flow, velocity, depth, turbidity, and suspended solids were measured, on seven occasions, at three sites along the historical spawning range of trout in the Styx River. Relationships based on flow were derived for the measured parameters. Velocity-dependent sedimentation data, and frequency-flow data for the Styx River, were used to predict sediment accumulation in clean gravels at each of the sites during egg incubation (c. 76 days).
Overall, sediment accumulation was predicted to increase downstream. The most likely scenario modeled suggests that redds in the most upstream site are marginally within acceptable levels, while redds at the middle site are probably severely impacted by sedimentation. The most downstream site is the worst affected of the three sites.
While logistical difficulties limited the range and reliability of data used, and modeling deficiencies also exist, the predicted patterns mirror changes in trout redd distribution and viability. The results are discussed in relation to a perceived decline in trout abundance and other observations suggesting this is caused by recruitment limitation. Management options to reduce sedimentation inputs to the upper Styx River are included.