Anadromous Salmonid Passage and Video Image Quality under Infrared and Visible Light at Prosser Dam, Yakima River, Washington

Abstract

The effect of infrared (>880 nm) and visible (400–700nm) illumination was compared to determine delay rates (percent of population) and delay times (min) of migratory chinook salmon Onchorhynchus tshawytscha, coho salmon O. kisutch, and steelhead (anadromous rainbow trout O. mykiss) in the fish ladder viewing chamber at Prosser Dam during the fall 1996 spawning season. Overall, a significantly (P < 0.05) greater proportion of migratory fish were delayed under visible (41%) than infrared illumination (28%). Species-specific comparisons indicated that significantly (P < 0.05) greater numbers of chinook and coho salmon were delayed under visible (57% and 33%, respectively) than infrared (25% and 12%, respectively) lighting. No significant difference was detected in the proportion of steelhead delayed under visible (35%) and infrared (25%). Passage rates for chinook salmon under infrared light were significantly (P < 0.001, chi square = 10.12) greater at night (70%) than day (30%), whereas under visible light nearly equal numbers of fish moved upstream during day and night (51% and 49%, respectively). Migrating chinook salmon readily passed through nonintrusive infrared but not visible light at night. Diel passage rates for coho salmon and steelhead were similar under infrared and visible light. Mean delay times for anadromous salmonids were short (<9 min) and similar in infrared and visible light. Infrared light facilitated anadromous fish passage at night but compromised video image quality and the ability to identify fish species and detect fin clips.