HUNTER: SPEED OF JACK MACKEREL 

 98 r 



Figure 1. — Probit lines for sustained speed threshold 

 for 6 hr of forced swimming at 18.5° C in juvenile 

 Trachurus symmetrieus. Upper panel, range fish length 

 10.0 to 11.9 cm iV = 127, probit = 0.077A' - 2.238; 

 lower panel, range fish length 9.0 to 17.6 cm, N =; 294, 

 speed expressed in L" ^/sec where L is the total length 

 of the fish, probit = 0.355:? — 2.958. 



To determine the form of the relationship 

 between the duration of the swimming period 

 and the ability to maintain a certain speed, 

 probit estimates of speed for five levels of fa- 



tigue were made for swimming periods varying 

 from 10 to 360 min. The form of the relation- 

 ship was about the same for all fatigue levels; 

 speed estimates declined exponentially with time 

 for short swimming periods and linearly with 

 time for longer ones (Figure 2). The point 



40r 



u 30 



UJ 



99% 



100 



200 300 



MINUTES 



Figure 2. — Relation between speed in L'^'^/sec and the 

 time it can be sustained for 1, 25, 50, 75, and 99 per- 

 cent fatigue levels in Trachelitis symmetrieus. Estimates 

 of speed for each fatigue level made at 10-min intervals 

 of cumulated time. 



of inflection from the exponential to the linear 

 relationship was examined in detail for the 50% 

 fatigue level. Probit estimates of the speed at 

 which 50% of the fish fatigued were made for 

 2-min intervals of swimming cumulated over 

 the first 100 min of observation. The data were 

 plotted on semilog paper and a line fit by eye 

 to the exponential function. The point of in- 

 flection appears to occur at about 22 min (Fig- 

 ure 3) . Thus, speed at which 50% fatigued and 

 the duration of the swimming period were ex- 

 ponentially related for durations up to about 

 22 min and were linearly related for longer pe- 

 riods of swimming. 



The performance of juvenile Tmchimis at 

 high speed was of interest. Fifteen fish 14.6 cm 

 mean total length (range = 13.4 to 16.6 cm) 

 swam at the highest speed used in the study 

 (160 cm/sec) for 2 to 6 min, mean time 3.4 min. 

 Thus, Trachurus 15 cm total length were able 

 to swim for about 3 min at about 10 L/sec or 

 about 32 L" Vsec. A slightly higher level of 



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