Response of Juvenile Coho and Chinook Salmon to Strobe and Mercury Vapor Lights

Publication Date



attraction, behavior, bypass, bypass systems, chinook, coho, environmental conditions, fish behavior, fish bypass, juvenile, light conditions, salmon, smolt

Journal or Book Title

North American Journal of Fisheries Management


Species-specific responses to flashing (strobe) and nonflashing (mercury vapor) lights were monitored in hatchery-reared juveniles of coho salmon Oncorhynchus kisutch and chinook salmon O. tshawytscha. Fish behaviors were characterized as attraction and avoidance responses, and as active, passive, and hiding behaviors. We investigated how basic fish behavior and activity changed when fish held under a variety of ambient light conditions were exposed to strobe and mercury light. Implications of how these behaviors may influence migrating smolts at a fish bypass system were discussed. Both chinook and coho salmon avoided strobe and full-intensity mercury light, but chinook salmon exhibited an attraction to dim mercury light. Coho and chinook salmon showed different behavior patterns under most conditions when exposed to strobe and mercury light: coho salmon hid 47% of the time, whereas chinook salmon swam actively 74% of the time. The greatest change produced by either of the stimulus lights was at night when both species normally were passive; exposure to mercury light at nighttime increased fish activity by 90%. Both species also showed similarities in their levels of excitability (e.g., sudden or explosive movements in otherwise sedentary behaviors). The results of this study showed that the behaviors were reproducible: more than 80% of the fish exhibited the same behavior during specific environmental conditions, and sudden and infrequent behaviors were strongly associated with these behavior categories. The behaviors observed in our experimental environment may give insight as to how changes in light relate to fish behavior in bypass systems.





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