Boggs: Bioenergetics and growth of Engraulis mordax 



565 



predicts metabolic rates in the middle of this range, in- 

 dicating that it may provide reasonable estimates for 

 engraulid metabolism. 



To use the model to estimate ration, the energy re- 

 quired for standard metabolism (Equation 11) and the 

 cost of swimming (Equation 13 converted to cal • g _1 

 • day -1 ) plus the energy needed for growth or repro- 

 duction, are multiplied by 1/0.65 (from Equation 6) to 

 account for X, I, and SDA. The result is the daily food 

 energy requirement. Similarly, 65% of food energy 

 minus standard and swimming metabolism gives the 

 surplus available for growth and reproduction at that 

 level of food intake and activity. 



Hunter and Leong (1981) estimated the food energy 

 requirements of 1-year-old anchovy (wet mass 10. 3g, 

 length 10.3cm) at 33.8 cal-g -1 day -1 (copepods at 

 4% of wet mass/day). According to the model in the 

 present study, X, I, and SDA remove 11.8 cal-g" 1 

 •day -1 , and standard metabolism (Equation 11) is 

 11.8 cal- g _1 • day -1 . Supposing 1 -year-old anchovy 

 swim at 12cm/s for 12 hours each day, this costs 0.45 

 cal  g _1 • h _1 (Equation 13), or 5.4 cal/g. If they swim 

 at 2cm/s for the other 12 hours, this costs another 0.4 

 cal/g, making the total swimming cost 5.8 calg -1 

 ■day -1 . Subtracting all these costs from the ration 

 energy leaves 4.4 cal • g _1 • day 1 , which Hunter and 

 Leong (1981) estimated to be enough for normal 

 growth plus 20 spawnings per year. 



Is this level of swimming activity realistic? Using 

 sonar tracking and Doppler shift analysis, Holliday 

 (1977) measured a relatively uniform swimming speed 

 averaging 45cm/s over a 40-minute interval for what 

 were thought to be northern anchovy about 14 cm long 

 (25g). To swim for 12 hours a day at this speed, while 

 maintaining normal growth and spawning 20 times per 

 year, 3-year-old anchovy (Hunter and Leong 1981) 

 would require a ration of 7.7% of body weight per day. 

 However, 3 hours a day at this speed, with the rest of 

 the day at 3cm/s, would allow for the same growth and 

 reproduction on a ration of only 4%. 



It appears that anchovy growth rates in nature and 

 the estimate of spawning 20 times per year (Hunter 

 and Leong 1981) are consistent with the current 

 study's model predictions for anchovy swimming at 

 speeds and consuming rations similar to those observed 

 in nature. Three aspects of the model were determined 

 by experiment: (1) A constant proportion of food 

 energy is available for metabolism and growth, (2) 

 metabolism increases with swimming speed, and (3) 

 gross energy conversion efficiency is a function of ra- 

 tion level and activity. The model should be useful in 

 estimating the effect of changing food abundance on 

 spawning frequency and growth, particularly as more 

 measurements of activity become available. 



Acknowledgments 



The laboratory work was accomplished at the South- 

 west Fisheries Science Center, NMFS, NOAA, La 

 Jolla, CA, while the author held a NOAA Resident 

 Research Associateship from the National Research 

 Council. I gratefully acknowledge the practical advice 

 and help provided by J.R. Hunter, R. Leong, and 

 S. Kaupp. J.R. Hunter, S. Kaupp, and D.A. Somer- 

 ton critically read the manuscript. 



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