The fishing of a highly cannibalistic species would remove older cannibalistic 

 specimens, thus relieving cannbalistic predation pressure on the juveniles. This 

 aspect of fishing has been studied numerically by Laevastu and Favorite (1976). 

 Most fish species are cannibalistic to some degree. The effects of a fishery on 

 cannibalism are briefly described in Section 3 on predation. 



The impacts of various intensities of fishing were studied numerically, using 

 the relations between the fishing effects and corresponding biomass parameter 

 changes determined in another numerical model (Laevastu I983). In the first 

 numerical examples, recruitment to the exploitable stock was assumed to be constant. 

 In the second set of computations, recruitment was made a function of fishing 

 (see Section 7). In reality, recruitment is quite variable in space and time, 

 and might mask most of the effects; thus, direct verification of the results in 

 the field with empirical data would be very difficult. 



3. SIMULATION OF PREDATION OF A SINGLE SPECIES POPULATION 

 Mortality due to being eaten by other, bigger fish (predation mortality), 

 constitutes the greatest part of the traditionally used "natural mortality". 

 Simulation of the dynamics of a single species population can be realistic only 

 if the predation upon this population is also simulated in a realistic manner. 

 A reasonably satisfactory simulation of predation is possible only in a holistic 

 ecosystem simulation such as PROBUB or DYNUMES, where the predations are simulated 

 in a detailed manner. 



In the present single species model, an attempt was made to simulate predation 

 on some known, but simplified, principles governing it as well as on the basis 

 of knowledge gained from the above-mentioned holistic ecosystem models. 



