and 1970 in spite of relatively low effort. This in- 

 crease was due to good catches made in higher 

 latitudinal waters off the South American coast. 



White marlin — The catch of white marlin de- 

 creased markedly after 1964. The average density, 

 shown by the catch per unit effort, also decreased 

 over the years. 



Blue marlin — The blue marlin showed a clearly 

 downward trend since 1962. The average density of 

 this species after 1965 fell to about one-fourth the 

 level in 1962 (Ueyanagi et al., 1970). 



Sailfish — The catch statistics also included some 

 longbill spearfish in this category. The yearly fluctu- 

 ations in catches have generally corresponded to the 

 Atlantic Ocean fishing effort. 



Some significant observations from the above are: 

 I) swordfish is the only species which has shown an 

 increase in the landings in recent years, 2) blue mar- 

 lin landings have decreased annually in the South 

 Pacific, Atlantic, and to a slightly lesser degree, also 

 in the Indian Ocean, and 3) the catch of the striped 

 marlin has fluctuated greatly from year to year. 



FUTURE PROBLEMS 

 IN BILLFISH RESEARCH 



The above-mentioned views on the trends of catch 

 for billfish species in relation to effort are based on 

 total hooks and not on the standardized fishing ef- 

 forts for the species. For this reason, the status of 

 billfish resources might not be reflected accurately. 

 Nevertheless, the catch trends suggest that some 

 species or stocks of billfishes are being rather heav- 

 ily fished. It is imperative that stock assessment 

 studies be pursued vigorously on these species. 



Other than in the eastern Pacific striped marlin 

 fishing grounds, the billfishes are being taken by the 

 longline fishery incidental to the major tuna species. 

 The fishery shifts according to the distribution of the 

 tunas, and for this reason, it is difficult to compile 

 adequate data on billfishes for analysis of the rela- 

 tionship between catch and effort. Since the longline 

 fisheries of Taiwan and Korea are becoming in- 

 creasingly significant, it is necessary that catch and 

 effort data from these countries be used along with 

 Japanese data for reliable stock assessment studies. 

 In other words, it is important to compile adequate 

 data on catch and effort for these fish, and also, 

 along with these studies, to clarify the population 

 structure of the various species. 



At this point, we might emphasize the importance 

 of studying the population structure of the striped 



marlin, not only because of its dominance in the 

 commercial landings, but also because of its impor- 

 tance in the sport fishery (FAO, 1972). Further- 

 more, from the biological point of view, several 

 characteristics encourage further study of this 

 species: 



1 . The large fluctuations in striped marlin landings 

 in the Pacific and Indian Oceans are believed to be 

 due to certain biological characteristics of the 

 species. For example, from studies of the striped 

 marlin in the northwestern Pacific it was found that 

 the average density tended to undergo biennial fluc- 

 tuations, probably caused by variations in recruit- 

 ment. A detailed study of such fluctuations can be 

 expected to contribute towards the understanding of 

 the population structure of the species. 



2. The distribution of the striped marlin in the 

 Pacific takes on a horseshoe-shaped pattern, cir- 

 cumscribing the tropical areas. This species, how- 

 ever, is distributed both in the tropical and subtropi- 

 cal waters of the Indian Ocean. Thus, while most 

 species of tuna and billfishes are distributed in the 

 same pattern in the major oceans, the striped marlin 

 seems to be an exception. 



The spawning areas are centered in subtropical 

 waters of both the North and South Pacific while in 

 the Indian Ocean, spawning seems to be centered in 

 tropical waters (Fig. 17). 



3. The differences in the distribution of the adult 

 striped marlin and in their spawning areas in the 

 Pacific and Indian Oceans may be indicative of a 

 process of speciation. This presents an interesting 

 problem in relation to studies on the billfish 

 phylogeny and hierarchy. 



For population identification, various approaches 

 such as tagging, morphometries, genetics, and 

 parasitology may be necessary. It is also important 

 to consider different and new approaches to this 

 problem. I discuss in greater detail in a separate 

 paper at this symposium (Ueyanagi, 1974) the possi- 

 bility that studies in larval morphology can contrib- 

 ute towards population identification. 



Because of the importance of the tuna fishery, 

 scientists have devoted their attention to the studies 

 of tunas in the past 10 years. Consequently, research 

 on billfishes is lagging considerably behind the 

 tunas. This International Billfish Symposium, how- 

 ever, may well be the turning point and we may be 

 able to look forward to increased effort towards the 

 study of billfishes. 



The billfishes, needless to say, are important both 

 to the commercial and sport fisheries. We must ac- 



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