DURBIN ET AL.: SWIMMING SPEEDS AND RESPIRATION RATES OF ATLANTIC MENHADEN 



In most measurements the distribution of 

 swimming speed observations showed small but 

 Statistically significant ( \2 <o.01 ) departures from 

 normality. These usually took the form of a slight 

 positive skewness, and leptokurtosis (data values 

 concentrated in the region of the mean). 



The variance of the swimming speed, which in- 

 cluded the variability shown by each individual 

 fish, as well as differences among fish, was posi- 

 tively correlated with the mean. However, the 

 coefficient of variation revealed that the fish were 

 relatively more variable in their swimming be- 

 havior when they were not feeding (Figure 3). 

 These results confirmed qualitative observations 

 during the experiments that the fish were least 

 excitable, and most consistent in their swimming 

 behavior, when they were engaged in feeding. 



With the exception of measurement no. 5, which 

 bracketed the transition from feeding to postfeed- 

 ing, the fish were very consistent in their swim- 

 ming behavior and respiration rate during indi- 

 vidual measurements. Thus the 95% CL about the 



50r 



5 40 



< 

 > 



O 30 - 



O 



77 20 



O 

 o 



10 



20 40 



SWIMMING SPEED, cmsec"' 



60 



Figure 3. — Relationship between mean and coefficient of var- 

 iation (a/x [100%]) in the swimming speeds of a school of 12 

 Atlantic menhaden during the initial and final, feeding, and 

 postfeeding measurements. 



estimates of mean respiration rate and swimming 

 speed during each of the measurements were 

 small, averaging ±8.9% of the mean respiration 

 rate and ±2.3% of the mean swimming speed. 



Initial and Final Measurements 

 (No. 1, 9, 10) 



These may be termed "routine" (Fry 1957) since 

 the fish were unfed and spontaneously active. Dur- 

 ing these measurements the fish swam slowly 

 about the tank without showing any strong school- 

 ing patterns. The mean swimming speeds and re- 

 spiration rates were very similar during the initial 

 and final measurements (Table 2). The range 

 among the mean voluntary swimming speeds of 

 the measurements was also fairly small, 10.5-15.2 

 cm/s (0.41-0.59 BL/s) (Figure 4). The range among 



40 



E 

 u 



a 30 



UJ 

 LU 



a 

 en 



o 



20 - 





10 - 



2_ 4 6 



X CHLOROPHYLL a 



^g. 



8 

 i-' 



10 



Figure 4. — Hyperbolic relationship between voluntary swim- 

 ming speed (S) of a school of 12 Atlantic menhaden feeding on 

 Ditylum brightwelli, and chlorophyll a concentration in the 

 water (A). The three measurements of mean swimming speed 

 obtained during the 7-h feeding period of each experiment are 

 plotted as a function of the mean chlorophyll a concentration 

 during each experimental feeding period. 



Table 2. — Swimming speeds (S) and respiration rates (R) of Atlantic menhaden in the feeding experiments and their 



regression equations. 



Measurements (periods) 



Initial (no. 1) 

 Final (no. 9, 10) 



Mean s 95% contidence limits 



Swimming speed 

 cm/s 



Respiration rate 

 mg Oz/g per b 



12.2±1.6 

 13.4±1.2 



10 ±0.009 

 0.093:^0.007 



Denved regressions 



Predictive 



Functional (GM) 



Feeding (no. 2. 3,4) 

 Postfeeding (no. 6. 7) 



log, oft = 0.0271 (S) - 1.446 

 r = 0.918. SE slope  



log,ofl = 0.0293 (S) - 1.276 

 r = 0.856, SE slope  



Equation (2) 

 0.0026 



Equation (4) 

 0.0062 



log,ofl = 0.0295 (S) - 1.534 Equation (3) 

 log,ofl = 0.0342 (S) - 1.342 Equation (5) 



881 



