Threshold values of river discharge and temperature for anglers' catch of Atlantic salmon, Salmo salar L
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The catch by anglers of adult Atlantic salmon, Salmo salar L., was studied over a 5-year period in the River Gaula, Norway. Atlantic salmon were caught over a wide range (23–570 m3 s−1) of the observed extent of river discharge (13–950 m3 s−1) and throughout the range of temperature (4–23 °C), but both factors strongly affected catch rate. Significant correlations between the number of Atlantic salmon caught daily, and water temperature (r = 0.33) and river discharge (r = −0.42) were found in 1987 and 1989, respectively. The highest daily catch occurred between 50 and 150 m3 s−1, and at temperatures between 13 and 16 °C. Threshold values for water discharge and temperature were found to exist at 250 m3 s−1 and 8 °C, with the highest catches below and above these values, respectively.