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 (  M o₂) 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 M o₂, which ranged from 8·74 to 12·63 mg O₂ 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 M o₂ 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 M o₂ or swimming economy. Such capabilities may be extremely important for timely migratory passages when salmonids face repetitive hydraulic challenges on their upstream migration.