13 



10. Indirect methods for forecasting fisheries potentials 



Although the actual techniques evolved have become extremely complex, 

 it is generally assumed that the following methods serve to aid in fore- 

 casting fishery potentials: 



• Estimates based on the general productivity of the oceans or areas 

 of oceans 



• Observations of eggs and larvae 



• Inferences from stomach contents 



• Direct observations of schools occupying the surface or deeper zones 



• Systemmatic sampling with fishing gear 



• Acoustic surveys 



(25) 



• Extrapolation from known areas. ' 



11 . Fishing Effort 



"As the abundance of the fish stock cannot be estimated by direct 

 measurement, the changes in abundance are assumed to be parellel to the 

 changes in catch rates of similar boats using the same techniques."^ ' 



There exist many other assumptions concerning assessment methodology 

 itself; they are necessary when one must depend on sampling techniques to 

 reach conclusions. However, in a "jery general sense the following factors 

 must be assumed in order to undertake fisheries assessments: 



• The biological system within which man operates is essentially stable 

 t Year-to-year data, when compiled, indicate long-term developments 



• Existing sampling techniques serve to identify many of those develop- 

 ments 



• Fish mortality as the result of man's harvesting activities can be 

 determined through the relationship between fishing effort and yield 



