-5- 



The growth rate of any species is reduced by the fraction of its food 

 requirement that it could not obtain in the current month, (SCj^ - 0.01, where 

 SC is a percentage). This adjustment is thus dependent on the biomass of the 

 species itself (i.e., its food requirement), and the biomass of the other species 

 which provide, or remove, potential prey items. This effect is assumed to be 

 linear, following Jones and Hislop (1978). 



To provide for density dependent growth once the equilibrium position has 

 been reached, the growth for each species is adjusted by the ratio of the 

 equilibrium biomass of that species (V^) to its mean biomass in the previous 

 year, (BB ). This ratio is divided by 12 to correspond to the monthly growth 



IN , , 



coefficient. The natural logarithm of this ratio is taken to correspond with 

 growth, which is expressed as an instantaneous rate. 



Density dependent growth has not been identified as a universal characteristic 

 of fish species and potential researchers will have to consider the suitability 

 of this equation in their own situations. Implicit in the use of this equation 

 in this instance is the assumption that decreases in the biomass are linked with 

 reduction in the percentage of adults in the population (e.g., resulting from 

 fishing mortality). Individual growth rates decrease with increasing age 

 (Paloheimo and Dickie 1965) thus the decrease in mean age of the population will 

 produce an increase in mean biomass growth rate. 



NATURAL MORTALITY {GHS^ ^) 



Natural mortality excludes that due to predation, which is computed separately, 

 It includes spawning stress and senescent mortality, together with residual 



