In many cases the records pertaining to sharks are completely lacking so it is 

 impossible to show the shark fishing situation in terms of catch rates. 



15, Area of 35° to 40° N. 



150° to 180° E. 



This sea area is also for the most part under the direct influence of the North 

 Pacific Current, and the currents flow generally eastward at all seasons of the year. 



Since the ocean currents eire thus comparatively uniform, there is also little 

 variation in the distribution of water temperatures and salinities and the isotherms generally run 

 parallel to the parallels of latitude, 



o 



During the winter, when the water temperatures are at their lowest, the 15 C. 



isotherm appears along the line of 35 N. and the 10 C. isotherm parjdlels roughly the line of 

 o o 



40 N. In the sumnner, when the water temperatures are at their highest, the isothernn of 20 C. 



runs along the line of 40 N. latitude and the 25 C. isotherm is in the vicinity of 35 N. Since 



these isotherms reach somewhat higher latitudes at the extreme western side of this sea area 



than they do to the eastward, they descend from west to east in a very gentle slope. 



The extreme western part of this sea area is fannous as a broadbill ground, the 

 season being in November and December. In addition to broadbill, striped marlin are abundant, 

 and their fishing season is in September and October, There is a flourishing shark longline 

 fishery which takes principally rakudazame (mokazame) (Isurus nasus) and the great blue shark. 

 This fishery has two seasons, one in the winter and one in the summer. To the ea^t of the area 

 there are excellent albacore grounds. The albacore fishing season in thi« sea area is sonnewhat 

 earlier thjui that on the grounds to the south and is of shorter duration. Some bigeye tuna are 

 also taken. Hardly any black tuna are taken and yellowfin are also extren-iely scarce, but de- 

 pending on the location considerably better catches are sometimes nnade than are found between 

 30° and 35° N. 



If this sea area is divided into three sections each of 1 of longitude, the general 

 outline of fishing conditions within each section is as follows: 



(a) 



150° to 



60°E. 



longitude 



The following table summarizes the data fronn surveys carried out in this section. 



Table 97. — Fishing conditions at 150° to 160° E.(35° to 

 40° N. ) 



The overall average catch rate is slightly more than 3. 5, to which a shark catch rate 

 of 1 , 8 may be added. The composition of the catch, aside from sharks, is 44 percent albacore, 

 41 percent spearfishes, and 11 percent bigeye tuna, with yellowfin making up the greater part of 

 the remainder. 



o o 



If the catch rates given above are compared with those in the area of 30 to 35 N. , 



which adjoins on the south, we find a markedly lower rate for black tuna, a notable increase in 



yellowfin, somewhat of a drop, although no great difference, in the case of the bigeye tuna, a 



conspicuous decline in albacore, and a value approximately 3 times greater for spearfishes. 



126 



