Discard rate is a function of the rate of shrimping effort (eg), bottomfish 

 standing stock (Q9), and the ratio of bottomfish catchability to shrimp 

 catchability (b): 



B = be 8 Q 9 . 



Remineralization is treated as a simple function of respiration rate: 



N j = n j R j' 



where nj is the ratio of nitrogen released in excrement (or bacterial excretions, 

 in the case of the detritus compartments) to carbon dioxide released in 

 respiration from each organic compartment except phytoplankton. 



FLOW-BALANCING PROCEDURE 



Flows and rate-coefficients were calculated by an iterative top-down flow- 

 balancing procedure that was based on three assumptions : 



1) The system at present is in steady state (over the long term, standing 

 stocks are neither growing or declining). 



2) Animals with several food sources feed no ns elect ively on these sources 

 in a proportion that is equal to the proportion of the standing stocks of these 

 food sources in the environment. 



3) Selectivity can be approximated by differential "weighting" of two or 

 more feeding flows to the predator. 



In the steady-state situation, the inflows to a compartment equal the 

 outflows. Total inflows to a compartment can, therefore, be determined if the 

 total outflows are known. The assumption that relative feeding rates on 

 alternative food sources are equal to relative standing stocks of these food 

 sources allows the inflows to a compartment to be apportioned among food sources. 

 If selectivity is considered important, the apportionment can be weighted 

 accordingly. The equations for calculating flows and setting rate-coefficients 

 by this procedure are as follows: 



x j =2(Qj A i,j>/£ p j,i» 

 *i,j =XjQiWi,j. 



P'i.j = AijPi.j 



c i,j ■ ( X j w i,j>/Qj- 



Flow balancing must start at the top of the food web with animal groups 

 that experience no significant predation or where the predation level can be 

 estimated independently. (In this particular case I started the flow-balancing 

 calculation with the large scavenger compartment.) The essential inputs for 

 determining flows and setting rate-coefficients by the flow balancing method 

 are (1) standing stocks for all compartments, (2) respiration rate-coefficients 

 for all animal compartments, (3) either respiration rate-coefficients or rates 



187 



