SUSTAINED SPEED OF JACK MACKEREL, Trachurus symmetricus 



John R. Hunter' 



ABSTRACT 



Jack mackerel, Trachurus symmetricus, were forced to swim for up to 6 hr at various speeds in an 

 activity chamber. The probit estimate for the swimming speed at which 50% of Trachurus would fa- 

 tigue during 6 hr was 93.4 cm/sec (8.4 L/sec) for fish 10.0 to 11.9 cm and was 22.4 L^'^/sec for fish 

 9.0 to 17.6 cm where L is the total length of the fish in centimeters. At higher speeds, Trachurus, 15 

 cm, swam for 3 min at 160 cm/sec or 10 L/sec. The swimming speed at which 50% fatigued declined 

 exponentially with time for about the first 22 min of swimming and thereafter declined linearly with 

 time. The possible significance of the time-speed relationship for Trachurus is discussed. 



Although a substantial literature on the swim- 

 ming speed of fishes exists (see Bainbridge, 

 1958; Gray, 1968), few reliable estimates of 

 maximum sustained speed exist. Much of the 

 literature on swimming speed of fishes is con- 

 cerned with estimates of maximum speed or 

 burst speed, that is, speeds that can be main- 

 tained for only a few minutes or less. A sus- 

 tained speed implies, on the other hand, that 

 the animal is capable of swimming at that speed 

 for hours. For example, Brett (1967) recom- 

 mended a minimum of 200 min for a fixed sus- 

 tained speed test. Fairly wide agreement exists 

 that 2 to 3 L/sec can be maintained for an hour 

 or more and salmonids and herring seem capa- 

 ble of sustaining 3 to 4 L/sec for such periods 

 (Blaxter, 1969) . These conclusions were drawn 

 primarily from studies of freshwater fish and 

 salmon; no estimates of maximum sustained 

 speeds have been made for fast-swimming pe- 

 lagic marine forms. The object of this study 

 was to determine the sustained speed thresh- 

 hold of jack mackerel, Trachurus symmetricus, 

 a pelagic marine fish of commercial importance. 

 The body form and musculature of Trachurus 

 appear to be designed for greater hydrodynamic 

 efficiency at high speeds than other species here- 

 tofore studied. In Trachurus, lateral muscula- 

 ture is concentrated in the anterior portion of 

 the trunk, and inserts by tendons on a small 

 deeply forked caudal fin. 



' National Marine Fisheries Service Fishery-Ocean- 

 ography Center, La JoUa, Calif. 92037. 



Manuscript received January 1971. 



FISHERY BULLETIN: VOL. 69, NO. 2, 1971. 



In addition to the interest in comparing the 

 sustained speed capabilities of Trachurus with 

 that of fish with other body forms, sustained 

 speed data have significance in prediction of 

 migratory capabilities and physiological limits. 



APPARATUS AND METHODS 



The apparatus used in the experiments was 

 an activity chamber provided with a water cur- 

 rent of various calibrated speeds. The appa- 

 ratus was the same as the one described and 

 figured by Hunter and Zweifel (1971) in this 

 issue except that a port was provided in the 

 transparent hatch of the swimming chamber 

 so that fatigued fish could be removed by hand 

 from the downstream screen without reducing 

 the flow in the chamber. The error in estimating 

 the water speed in the swimming chamber did 

 not exceed 10% and it was assumed that the 

 fish were swimming at the estimated speed. 



The experimental design was essentially the 

 same as that used by Brett (1967) for deter- 

 mining the sustained speed threshhold for sock- 

 eye salmon, Oncorhynchus nerka. Fifty-five 

 groups of five Trachurus (9.0 to 17.6 cm total 

 length, mean = 12.43 ± 0.11 cm) were subjected 

 to a fixed speed of 38 to 160 cm/sec for 360 min 

 or longer after an introductory period of about 

 30 min at a low speed. A time-lapse camera 

 photographed the fish at 1-min intervals and 

 the time to fatigue for each fish was determined 

 from the photographs. The temperature of the 

 water in the activity chamber and in the holding 



267 



