An evaluation of the use of critical swimming speed for determination of culvert water velocity criteria for smallmouth bass
swimming, water velocity, fishways, culverts, bass, respirometer, raceway, swimming speeds, fish length
Journal or Book Title
Transactions of the American Fisheries Society
Critical swimming speed (Ucrit) is a common measure of the relationship betweenexercise intensity and duration within the prolonged performance envelope. This relationship isoften used to establish water velocity criteria for fishways and culverts; however, the techniqueinvolves the assumptions that fish will choose to move at (1) a swimming speed equivalent toUcrit and (2) a ground speed that results in a passage time equal to the interval used in the criticalspeed protocol. The objective of this study was to evaluate the validity of these assumptions andthe usefulness of velocity criteria based on critical speed data in predicting passage success. Toaccomplish this, I measured the critical swimming speed of wild smallmouth bass (Micropterusdolomieu) in a respirometer and the relationship between the water velocity and swimming speedof fish in a 50-m raceway. The latter was then used in conjunction with the former to calculatewater velocity criteria based on ground speeds actually attained by fish, thereby eliminating thesecond assumption. Critical swimming speeds ranged from 65 to 98 cm/s and were positivelycorrelated to fish length (24-44 cm). Swimming speeds attained by free-swimming fish in theraceway increased significantly with water velocity. Maximum allowable water velocities forraceway fish (adjusted appropriately for expected swimming speed) ranged from 54 to 63 cm/s,depending on fish length. Despite this, the proportion of individuals that made complete ascentsagainst water velocities ranging from 40 to 120 cm/s was high (82-95%), and the probability of asuccessful ascent did not change significantly with water velocity, fish length, water temperature,exposure time, or time in captivity. As such, it is concluded that critical speed should not be usedto set culvert water velocity criteria for this species.