PAULY: ESTIMATING FOOD CONSUMPTION OF FISH POPULATIONS 



90 



t w w 



'o ' r » i 



max 



-50 



-10 o 10 

 Input change (%) 



50 



Figure 3.— Sensitivity analysis of Equation (22), based on parameter estimates in Table 4 for 

 Epinephelus guttatus. Note strong effects of changes in /?, intermediate effects of K and Z, and 

 negligible effects of W max , W r , and t . 



Table 2.— Properties and parameter values of Epinephelus gut- 

 tatus and Holacanthus bermudensis relevant to the computation 

 of their food consumption (based on data in Menzel 1958, 1960; 

 See Table 1 and text). 



1 From Thompson and Munro (1977); Z = 0.64 refers to an unfished stock 

 and is thus an estimate of M. 



2 From data in Table 1 and Equation (13). 



3 Based on method in Pauly and Munro (1984) and on growth parameter 

 estimates pertaining to members of the related family Acanthuridae, in Pauly 

 (1978). 



4 Assumed; has little influence on results (see text and Figure 3). 



Corresponding to a fish of 1 g with growth parameters W^, K, and f as 

 given. 



6 See text and Figure 2. 



7 Based on equation (11) in Pauly (1980), with T = 28°, L„ = 30 cm, K = 

 0.25, and M = Z. 



e Assumed; has little influence on results (see text and Figure 3). 



QUANTITIES OTHER THAN QIB 

 ALSO ESTIMATED BY THE MODEL 



In addition to estimating QIB, the model presented 

 above can be used to obtain other useful quantities; 

 namely, 1) maintenance ration and related informa- 

 tion, and 2) trophic efficiency. 



Although there are differences between authors, 

 maintenance ration is usually defined as the food 

 used by fish to just maintain their weight at some 

 "routine" level of activity. Usually, maintenance ra- 

 tion is estimated by feeding fish over a wide range 

 of rations and determining by interpolation the ra- 

 tion generating neither weight gains nor losses 

 (Jones 1976). 



The model presented here allows the estimation 

 of maintenance ration (even if fish have been fed 

 constant rations) through extrapolation of weight- 

 specific estimates of QIB, such as presented in 

 Figure 4 to the size W^, i.e., to the size at which, 

 by definition, all food consumed by a fish is used for 

 maintenance. In the case of the feeding data on E. 

 guttatus analyzed here, an estimate of daily main- 



833 



