Power Output of Two Sizes of Atlantic Salmon (Salmo Salar) at Their Maximum Sustained Swimming Speeds

The maximum sustained swimming speeds (U_ms) for large (0.45 m long) and small (0.15m) Atlantic salmon were respectively 0.91 ms⁻¹ and 0.54ms⁻¹. Video and ciné films of fish swimming close to U_ms were analysed to obtain variables required for the application of two hydrodynamic models, those of Lighthill and Yates, to determine the mean thrust and mean power output at these swimming speeds (U) close to U_ms. A large fish (‘Salmon’) and a small fish (‘Smolt’) were selected for analysis. For salmon using Lighthill’s model, and ⁠, and using Yates’ model, and (U=0.87ms⁻¹=0.96U_ms). For smolt using Lighthill’s model, and ⁠, and using Yates’ model, and (U=0.37ms⁻¹=0.69U_ms). The power output for smolt swimming at 0.69U_ms was corrected to that required to swim at U_ms, giving (Lighthill’s model) and (Yates’ model).

At U_ms it was assumed that all the red muscle was used. Two fish were selected from each size group and cross-sectioned to estimate their red muscle masses. Using a maximum mass-specific power output of 5–8 W kg⁻¹ for slow red muscle fibres allowed us to calculate that the large and small fish have a power output capacity of 0.125–0.3 W and 0.007–0.019 W, respectively.

The power output values at U_ms derived from the different approaches for the large (0.25–0.26 W) and small (0.0059–0.0074 W) salmon agree closely. Effects of scaling are discussed.