"Percentage" does not represent the catch rate but the proportion of the fish caught which were 

 taken on long and short branches. 



The long branches were 99 feet long and there were two of thenn per basket of gear. 

 The short branches were 30 feet long and there were four per basket. There was one 90-foot 

 float line to each basket. 



Table 112 shows that even in three different regions there was little variation in the 

 proportions of fish taken by the two kinds of branch lines. Since there were twice as many short 

 branches as long branches, the catch rate of the long branches was 5 to 6 times that of the short 

 bramches. There are almost no such data for Japanese waters, but a certain amount of similar 

 data was gathered in southern waters by the Shonan Maru and other research vessels. These 

 data show a rather clear tendency for the catch rates for the tunas to be greater the deeper one 

 goes, at least down to 100 meters, for the spearfish catch rates to be greatest at 50 to 60 meters, 

 and for the shark catch rates to be greatest at shallow levels. 



Most of the gear used by research vessels in exploratory fishing falls into three gen- 

 eral categories. As a matter of fact, however, in many cases there are inadequate records of 

 the gear that was used and for nnuch of the data we do not know what type of gear was employed. 

 Of the three types of gear, one is the albacore line, and the other is a line specially designed to 

 catch spearfishes and sharks. The third type is that generally used to catch tunas amd spear- 

 fishes. However, although we may say there are three types, it is not a matter of each type 

 having a connpletely different construction, but simply that they differ with regard to the number 

 and length of branch lines, the length of float lines, the shape of the hooks, ajid so forth. 



On the albacore lines employed in the past, the brainch lines were short and numerous. 

 The number of branch lines was not standardized but ranged from 10 to 20 or 30 per basket. 

 For the most part, about two long branch lines, called " burakuri" , were hung among the short 

 branches. The short branches were mainly intended to take albacore, while the burakuri were 

 for catching bigeye tuna or other tunas and spearfishes. In the longlines designed to take shark* 

 and spearfishes, the branch lines were short and most such gear had about nine branches per 

 basket. The third type of gear, that commonly employed, has four to six branch lines per basket, 

 the length of which is generally greater than those of the other two types of line. 



From the geographical and seasonal point of view, we may say in a very general way 

 that in the winter in waters north of 25 N. latitude, the gear used was almost entirely albacore 

 line. To the south of this latitude, ordinary longlines are used throughout the year. The use of 

 spearfish and shark longlines is comparatively localized, such gear being found in Formosan 

 waters, west of Kyushu, ajid in the waters of northeastern Honshu and Hokkaido, The gear for- 

 merly used around Tanegashima to take black tuna was of a peculiar design. 



Except for the slight amount of data presented above, almost nothing is known at the 

 present time with regard to the question of what effect the length of the branch lines, or in other 

 words, the depth at which the hooks hang, has on the catch rate for the various species. It is 

 said that bigeye tuna are more often caught on long branch lines, or that spearfishes are more 

 often caught in the shallow levels and so forth, but hardly any scientific demonstration of these 

 facts has been made. Taking albacore lines as an example, black tuna, yellowfin, bigeye tuna, 

 spearfishes, and sharks are all caught on this gear. If all species other than albacore were 

 caught on the so-called burakuri and if the albacore were always taken on the short branch lines, 

 the catch rate by species could be accurately calculated. However, as a matter of fact, all 

 species are talcen both on the short lines and on the burakuri. Consequently, in calculating the 

 catch rates, the total number of branch lines, or in other words the number of hooks employed, 

 must be used. 



As was said earlie r, it is thought that the effect of fishing gear construction on catch 

 rates is not to be regarded lightly, and it is naturally to be considered that some correction for 

 differences in gear construction is necessary in comparing catch rates for each species. 



138 



