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constant flux and extremely difficult to generalize. The interrelation- 

 ship between these factors and marine organisms appears to be critical, 

 yet the data presently established may be too "spotty" to develop useful 

 conclusions. 



6. Survey Tows 



As opposed to other sampling methods, this method, usually undertaken 

 with gear similar to commercial gear and utilized in the same manner, 

 seeks to determine the age and abundance of various groundfish or pelagic 

 fisheries resources for commercial purposes. The method depends upon 

 statistical models that have been developed for fish population dynamics. 



Advantage : Such surveys can offer immediate indications to commercial 

 fisheries of resource potential as well as year-class strength. 



Disadvantage : The biases inherent in such a sampling scheme are 

 numerous. Such survey tows determine the average weight, size, age, and 

 sex of the species being studied, utilizing statistical formulations, and 

 then go on to estimate the size of that species for commercial purposes. 



7. Effort Data and Catch 



The relationship between stock size and fish mortality becomes criti- 

 cal when utilizing assessment information to determine sustainable yield, 

 and fishing mortality is determined by the weight of the catch and the 

 effort needed to produce it. The assumption here is that when more effort 

 produces less fish, the stock is in a depleted condition. 



Catch data is determined through analysis of reported landings, 

 skipper's logs, random surveys, estimates of species discarded, estimates 



