ABSTRACT 



A summary of methods used by various investigators to estimate the fishing depth of longline is 

 given. Sounding tubes, used by POFI in conjunction with studies of albacore tuna, Germo alalunga 

 (Bonnaterre), in the central North Pacific, measure the depth of the longline with considerable ac- 

 curacy. A method, using readings provided by the tubes, is developed so that the observed "hang" 

 of a given basket of gear and the theoretical "hang" can be compared. The results obtained suggest 

 that the configuration of the mainline in the individual baskets does not conform to a catenary. We 

 conclude that the skewness in the shape of the line did not occur during the fishing period, but rather 

 during retrieving operations when slack formed in hauling allowed a portion of the gear to sink below 

 the maximum fishing depth. It is suggested that distortions related to retrieving procedures can be 

 overcome. A method is presented by which the maximum fishing depths for individual hooks along 

 an entire set of gear can be estimated. 



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