Field-based measurements of oxygen uptake and swimming performance with adult Pacific salmon using a mobile respirometer swim tunnel

Novel field measurements of critical swimming speed (U-crit) and oxygen uptake (Mo-2) in three species of adult Pacific salmon Oncorhynchus spp. up to 3.5 kg in body mass were made using two newly designed, mobile Brett-type swim tunnel respirometers sited at a number of field locations in British Columbia, Canada. Measurements of U-crit, which ranged from 1.68 to 2.17 body lengths s(-1), and maximum Mo-2, which ranged from 8.74 to 12.63 mg O-2 kg(-1) min(-1) depending on the species and field location, were judged to be of similar quality when compared with available data for laboratory-based studies. Therefore high quality respirometry studies were possible in the field using adult wild swimming salmonids. In addition, the recovery of wild adult Pacific salmon from the exhaustive U-crit swim test was sufficiently rapid that swimming performance could be repeated with <1 h of recovery time between the termination of the initial swim test and the start of the second test. Moreover, this repeat swimming performance was possible without routine Mo-2 being reestablished. This result suggests that wild adult salmon are capable of carrying a moderate excess post-exercise oxygen consumption without adversely affecting U-crit, maximum Mo-2? or swimming economy Such capabilities may be extremely important for timely migratory passages when salmonids face repetitive hydraulic challenges on their upstream migration. (C) 2003 The Fisheries Society of the British Isles.