Effect of Turbidity on the Predator Avoidance Behaviour of Juvenile Chinook Salmon (Oncorhynchus tshawytscha)

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Abstract
The effect of turbidity on the predator avoidance behaviour of juvenile chinook salmon (Oncorhynchus tshawytscha) was determined in controlled laboratory experiments. Bird and fish models were used to simulate predator risk. In the absence of risk, juvenile chinook were distributed randomly within an experimental arena in turbid conditions (≈23 NTU), but in clear conditions (<1 NTU) they associated with the bottom. When introduced to bird and fish predator models, the chinook altered their distribution and occupied deeper parts of the arena regardless of turbidity level. However, their responses in turbid conditions were less marked and of shorter duration. Turbidity apparently reduced the perceived risk of predation in juvenile chinook.