the tunas were found to be contaminated with 

 radioactivity. When this became widely known the 

 market for tunas was seriously affected. In order to 

 avoid a drastic drop in tuna prices, the processors 

 discovered new uses for the fish, including their use 

 in manufacturing tuna sausages and hams. These 

 products gained wide popularity over the next de- 

 cade. Along with tunas, the blue marlin and black 

 marlin were also utilized in this manner. The price of 

 blue marlin and black marlin increased steadily 

 through 1965 when the production of fish sausage 

 and ham reached its peak. The price then leveled off 

 between 1965 and 1967, but began increasing again 

 after 1967. The latter increase was related to new 

 developments in the tuna longline fishery. 



Beginning around 1967, Japanese tuna longliners 

 fishing for southern bluefin tuna were equipped with 

 refrigeration facilities which permitted fish to be fro- 

 zen rapidly to temperatures of -55°C or lower, and 

 also with fishholds capable of holding fish at temper- 

 atures below -40°C. Fish could then be brought 

 back to Japan from distant grounds in excellent con- 

 dition. Billfishes brought back under such refrigera- 

 tion were acceptable as sashimi and fish steaks. This 

 new use gained wide popularity and presently is the 

 common form of utilization in Japan. The striped 

 marlin is particularly valued as sashimi and, like the 

 southern bluefin tuna, commands very high prices. 

 In general, billfishes larger than about 30 kg are 

 used as sashimi. One of the advantages of billfish 

 flesh is that it does not undergo as much color change 

 as that of tunas. It can thus withstand longer periods 

 of transportation and possesses a longer market 

 shelf-life than tuna. 



The principal utilization of billfishes, by species, 

 is as follows: 



Striped marlin — virtually all used as sashimi; 

 remainder in sushi. 



Blue and 



black marlins — virtually all as sashimi. 



Swordfish — steak, sashimi. 



Sailfish — those over 30 kg as sashimi; 



others in sausages and hams. 



Shortbill spearfish — fillets for use as steak ; 

 broiled or baked. 

 Of all the billfishes landed at the Tokyo Fish Mar- 

 ket, roughly one-half are consumed in the city of 

 Tokyo; the remainder is distributed throughout 

 Japan from Hokkaido to Kyushu.' 



'Information on value and utilization of billfishes was provided by 

 Mr. Hiroyo Koami of the Tsukiji Fish Market Co. Ltd., Tokyo. 



DEVELOPMENT OF 

 THE LONGLINE FISHERY 



As described earlier, virtually all of the commer- 

 cial catches of billfishes are made by the longline 

 method; only a negligible amount of surface- 

 swimming billfish is taken by the harpoon fishery. 

 The longline gear seem most effective in capturing 

 the deep-swimming billfishes. 



The regular longline operation involves a set of 

 gear whose mainline extends over a distance of 25-75 

 km at the surface of the ocean. Branch lines with 

 baited hooks, numbering about 2,000 per set, hang 

 vertically from the mainline, which is suspended at 

 the surface by float lines and buoys. The baited 

 hooks usually hang at depths of 100-150 m. The gear 

 is set very early in the morning and its retrieval, 

 which begins around noon, takes many hours, with 

 completion frequently well past midnight. 



There is a special type of "night longlining" which 

 is aimed principally at catching swordfish. This is, as 

 the name implies, an operation in which the gear is 

 set at night. Compared to the typical tuna longline, 

 the night longline gear is set to fish much shallower 

 by the use of additional floats and shorter gear ele- 

 ments. Another difference is in the use of squid as 

 bait rather than the saury, Cololabis saira, which is 

 preferred for regular longlining. 



Longlining has the advantage of not having to rely 

 on live bait. This gives the fishery a great deal of 

 mobility. The tuna longliners can roam the world's 

 oceans, fishing distant waters in pursuit of the de- 

 sired species offish. Another advantage is that there 

 is a minimum amount of gear selectivity, in that small 

 to large fish of various species can be taken by this 

 method. 



The longline fishing grounds have rapidly ex- 

 panded over the years. Although the longline fishery 

 was aimed principally at the various species of tunas, 

 with the expansion of the grounds, more and more 

 billfishes came within range of the fishery. The fish- 

 ing ground expansion is shown in Figures 4, 5, and 6. 



Pacific Ocean 



Before 1955 the fishery was centered in the central 

 and western Pacific Ocean (Fig. 4), where it ex- 

 ploited the striped marlin of the northwestern Pacific 

 and the blue marlin in the equatorial region. This 

 fishery also began to catch striped marlin of the 

 southwestern Pacific and the black marlin in the 



