Swimming endurance of haddock (Melanogrammus aeglefinus L.) at prolonged and sustained swimming speeds, and its role in their capture by towed fishing gears

This paper describes an experiment to determine the swimming endurance of haddock (Melanogrammus aeglefinus) at prolonged swimming speeds. Fish were stimulated to swim in a circular path around an annular tank, using a moving light pattern to trigger the optomotor response. Individually tagged haddock (length range 16.0–40.2 cm) swam in groups over a range of speeds (0.3–0.9 m s−1) and at a constant temperature (9.85 ± 0.07°C). Endurance of individual fish was shown to be related to their swimming speed and length. However, there was also significant variation (p < 0.05) in the performance of fish of approximately equal length. Distinct behaviours and swimming gaits were also identified and associated with the performance of individual fish. The inverse-linear model is introduced, as an alternative to the log-linear model, for describing the relationship between swimming speed and endurance, and estimating maximum sustainable swimming speed (Ums). Estimates of Ums ranged from 0.38 ± 0.03 m s−1 and 3.16 ± 0.02 BL s−1 (for a 16.0-cm fish) to 0.62 ± 0.04 m s−1 and 1.51 ± 0.07 BL s−1 (for a 42.0-cm fish). Ums represents an important threshold in the behavioural physiology of fish, marking the upper limit of aerobic swimming. The relevance of these results and Ums to the fish capture process is discussed.