with the Increasing demand for t'ana products, operations In home waters approached 

 their practical maximumi and It hecame evident that a further increase In production would 

 require exploitation of new fishing grounds. During the decade prior to World War II the 

 Japsmeee tuna clipperc ranged throughout the entire western Pacific Ocean, as far east as 

 the Hawaiian Islands, south to the areas around New Guinea and the Dutch East Indies, and 

 southwest into the Indian Ocean. Many of the voyages, especially to the Indo-Paciflc region 

 and the Mandated Islands area, were surveys made to determine the heet fishing grounds for 

 future exploitation. Since the alhacore had the greatest export value of all the tunas, 

 fishing grounds for this species were surveyed and became more extended each year. The mid- 

 Pacific area proved to he an important fishing ground for the winter alhacore. Major fish- 

 ing grounds for the yellowfln tuna and marline 3/ were located in the tropical zone, and in 

 19?e commerclsil fishing by vessels based in Japan was started in the Mandated Islands area. 

 Tuna fishing was also conducted near the southern California coast. The amount of catch in 

 Hawaiian and California waters was insignificant as the trips to these localities were pri- 

 marily naval operations. 



The extent of Japanese operations in various fishing areas can be realized from the 

 general tun?, survey conducted by the Tokyo Central Fisheries ISxperimental Station in 1939. 

 The data permit determination of the comparative amounts of the total catch obtained in each 

 of eight major fishing regions (Figure 4). It is evident that the distant offshore tuna 

 fisheries, despite the efforts of the fishermen and encouragement by various government 

 agencies, were undeveloped emd never reached the proportions attained in Japanese home waters. 

 The chief limitation was the curtailment by the Japanese array and navy of fuel allotments 

 to the larger fishing vessels. In order to conserve fuel, plans were under way for opera- 

 ting mother-ship fleets, as the salmon and crab induetries did in northern waters, but they 

 did not materialize because of the outbreak of the war. 



The present publication is a digest and analysis of the information obtained from the 

 Japanese on the tunas. It is based on a survey of available literature, conferences with 

 research personnel auxd Bureau of Fisheries officials, and dlBcuesions with fishermen. 

 Because of the difficulty of translating much of the original oiaterial into English, this 

 report will be augmented by future work. 



Heallzlng the importance of the fisheries, the Japanese have completed numerout studies, 

 especially on the comn.ercially valuable species, but their research has been guided mainly 

 by efforts to locate areas of greatest concentration. Considerable oceanographlc data have 

 been accumulated for several of the species, but, here again, for the primary purpose of 

 detemining the ccndltions under which the fish can best be found and caught. Information 

 on the life histories and migrations of even the better known species ie almost totally 

 lacking. Age and growth studies are still in the initial phases of investigation. The 

 types of fishing vessels and the fishing techniques used by the Japanese In the tuna fish- 

 eries are reported in considerable detf>ll. Available data on the economics of the fisheries, 

 pre- and postwar, are given, but the compilation of complete statistics has been neglected 

 by the Japanese, and the many gaps in their information prevent the presentation of a com- 

 plete picture. 



3/ Tuna lonjj line boats operating in the offshore pelagic waters take a large proportion 

 of the marlin, swordfish, and sallfish catch. Traditionally the Japanese include 

 these species in the tuna fisheries, without regard to biological relationships. This 

 practice often lends to difficultlee as this grouping generally has been followed in 

 compiling tuna fisheries statistics. Separation by species is rarelj"- made, and the 

 Japanese use the term "tuna" to Include all true tunas (maguro) plus these allied forms. 

 Occasionally marllns, swordfish, and sallfish are distinguished from the true tunas 

 and grouped into a separate category, the spearflshes (kajikl). 



10 



P-6307 



