An Evaluation of the Use of Critical Swimming Speed for Determination of Culvert Water Velocity Criteria for

,4bstruct.-Critical swimming speed (U,,,) is a common rneHsure of the relationship between exercise intensity and duration within the prolonged perforn~nnce nvelope. This relationship is often used to establish wntcr velocity criterin for fishways and culverts; however, the technique involves the nssumptions that fish will choose to move at ( I ) n swimming spced cquivulent to U,,, and (2) a ground speed that results in a passage time equnl to the intervnl used in the criticnl speed protocol. The objective of this study wns to cvaluute thc validity olthese assumptions nnd the usefulness of velocity critcrin based on critical speed dnta in predicting passage success. To nccomplish this, I measured the critical swimmin~ speed of wild smalln~outh bass Miuropter~i~ dolomieu in a respiromcter and Lhe relntionship helwecn the water velocity and swimming speed of tish in a 50-m rnccway. The lnttcr was then uscd in conjunction with the former to calculate wntcr velocity criteria hased on ground spccds ~ctually nttained by fish, thereby eliminating the second nssump~ion. Criticd swimming speeds rangcd from 65 to 98 c d s and were positively correlated to fish length (24-44 em). Swimming speeds atrained hy free-swimming fish in the raceway increased significnntly with wnter velocity. Maximurrl nllowable wnter velocities for rnceway fish (nd.jusred uppropriately for cxpccted swimming speed) rnngcd from 54 to 63 crnls, depending on fish length. Dcspite this. thc proportion of individuals that mnde cornpletc ascents ngainst water velocities ranging from 40 to 120 c d s wns high (82-95%), nnd the probnbility of a successful nscent did not chnnge signilicnntly with water velocity. fish length, water temperature, exposure rime, or time in cnptivity. As such, it is concluded that criticnl speed should not be used to set culvert water velocity criteria for this species.