20 



of the round weight of fish (landed fish have usually been cleaned and are 



thus lighter than when caught), and reliance upon similar information as 



provided by other governments (in international waters this has been the 



only data available to scientists, and, particularly when reporting catch, 



(30) 

 notably slow in reaching a conclusion). 



Effort data is a determination of how much fishing effort was 



expended to land the estimated and reported catch. Fishing effort may 



be expressed by days fished, number of tows with a trawl, catch per hour 



or day, size of vessel, horsepower of vessel, numbers of vessels, number 



of trawls in use within the designated fishery, the area "swept" by a 



trawl during its tow; all of which must then be converted to a single 



standard (as, for example, the "British trawler ton-hour") and applied 



to all the vessels operating in the area over a specified period of 



(31,32,33,34) 

 time. 



Advantage : Such data is absolutely necessary to calculate fishing 

 mortality. Many nations now require accurate reporting of such data by 

 their skippers, under relatively stringent international regulations, 

 although the variance among nations on this matter appears extensive. 



Disadvantage : The major problem here is again the accuracy of the 

 data, much of it reported and suspect, much of it tied closely to large 

 necessary assumptions that seek to standardize the efforts of the inter- 

 national fleet, much of it gathered too late for useful application, and 



(35) 

 much of it not available at all. 



