8 



III. BIOLOGICAL ASSUMPTIONS FOR MARINE RESOURCE ASSESSMENT* 



Although there exist several biological assessment models, and al- 

 though "...the methods used in fish population dynamics may differ 

 (Schaeffer, Holt and Beverton, Rickert, all of whose methods have been 

 refined and made more complex and exact by many special ists).. they are all 

 fundamentally similar. They consist of a mathematical formulation syste- 

 matically linking the main parameters of a fish population with the data 

 that can be collected."^^^^ 



These "parameters," however, cannot be interpreted without a clear 

 awareness of the assumptions behind them, although in some cases the 

 assumptions themselves are open to question, dispute, or doubt. Among the 

 assumptions utilized are the following. 



1 . Basic Theory 



P = KI P - production 



I - food intake of the prey 



K - prey gross production efficiency 



Y = FB Y - yield to predator 



B - average prey biomass 



F - grazing/fishing coefficient 



"...changes in predator numbers at different trophic levels lies in 



the fact that the yield to the predator is proportional to the average 



biomass of food particles present at a particular instant, and to the fact 



* Assessments for Georges Bank have been undertaken according to these 

 assumptions, utilizing the methods outlined later in this report. 



