food composition table for each predator, this gives the monthly consumption of 

 each prey group by the apex predators. This is removed each month irrespective 

 of the current biomass of any of the prey groups. In areas with high apex 

 predator biomasses this would need adjusting to allow prey switching in response 

 to prey availability. 



CONSUMPTION BY OTHER SPECIES (CC^^ ^) 



Food requirements of these species groupings are dependent on their growth in 

 the current month. Initial estimates of growth in any month are computed using 

 the previous month's values for the parameters in the biomass equation. Once 

 consumption is computed, the growth is recomputed. It is possible to recompute 

 consumption at this stage to reflect the updated growth, but in practice this has 

 not been found to affect the results. Thus the consumption is computed only once 

 in each month. The steps are as follows: 



Total Food Requirement of Each Species Grouping (FOOD ) 



The food requirement consists of a food requirement for growth and a food 

 requirement for maintenance. The food requirement for growth is computed from 

 the actual growth in biomass, (GRO) , that is, growth uncorrected by fishing 

 mortality, natural mortality, or consumption: 



GS 

 GRO = BBI 'Me '^''^ - 1) 



The maintenance requirement is computed as the maintenance requirement for 



the mean of the current and the previous month's biomass, BBI. An arithmetic 



mean is used following Ricker (1975, p. 239). Thus the total food requirement 



can be expressed as: 



FOOD,, =(BBI -'■ FRM -- 30) + (gRO " FRG) 

 N 



