Responses of Coho and Chum Salmon Fry to Current

Chum and coho salmon fry respond positively to changes in water flow by swimming against the current. The magnitude of the response varies with the intensity of the current. Currents eliciting optimum response differ for the two species. Both species respond to the stronger of two parallel laminar currents but, after a time, coho fail to discriminate between small differences while the chums move continuously into the greater flow. No evidence of adaptation is apparent in a two-hour period with rapid complex turbulences. In turbulent water coho fry make a sharper initial response than chum fry but do not seem to maintain the peak response over as wide a range of turbulences.