15 



(27,28,29) 

 IV. STOCK ASSESSMENT - METHODS 



For assessment of fisheries populations (potential size, standing 



* 

 stock size, etc.)> the following indirect methods are used. For each 



method, following a brief description, the basic advantages and disad- 

 vantages are discussed. It should be noted that resource abundance surveys 

 may be carried out with gear unlike that used by fisheniien, although 

 commercial surveys, to be of industry use, must use techniques and gear 

 similar to that used by the fishermen. 



1. General Productivity 



General productivity of the marine area being surveyed can be deter- 

 mined by measuring active physiological processes or by evaluating standing 

 stocks of phytoplankton. Various techniques seek to estimate: produc- 

 tion, uptake of C-14 in the system, or figures based upon the standing 

 stock of plankton. 



* 



For the Georges Bank area, the basis of most assessments has 



been data developed during the fall and spring survey cruises as 



well as foreign data from ICNAF. While the survey cruise data is 



relatively specific, to date the information from ICNAF--particu- 



larly for catch and effort data--has been uncertain, often false, 



and often is not available in time for management decisions that 



must be taken on a yearly basis. The mobility and harvesting 



capacity of distant water fleets is such that data time lags force 



management decisions to be made on the basis of information that 



is known to be incorrect. In the absence of changes brought about 



by man's fishing activities, such methods as outlined here would 



have by now generated considerably more precise information, but 



the perturbations i^esulting from man's activities have made historical 



data interpretation extremely difficult. 



