DEVELOPMENT AND CONSERVATION OF TUNA FISHERIES 159 



Intensive fishing of a tuna species in one part of a large geograph- 

 ical area, while it is unfished in other parts, can scarcely result in over- 

 fishing if the species consists of a single large population migrating 

 freely throughout the area. It may happen, however, that there are a 

 number of sub-populations, so that the fishery is bearing very heavily 

 on one or more of these while leaving the others untouched. In the 

 latter case, the sub-populations being fished may easily be overfished 

 while the others remain untouched. 



Like much else concerning the biology and life history of the tunas, 

 the degree of distinctness of the tuna populations of the several regions 

 of the Pacific is imperfectly known. For the yellowfin tuna, it has been 

 fairly well demonstrated by morphometric studies by Godsil and Green- 

 hood (1951), Schaefer (1952) and Royce (1953) that the yellowfin 

 tuna of the Eastern Pacific are distinct from those of other parts of the 

 Pacific. Royce's work shows that there are also further distinctions be- 

 tween populations in other regions of the Pacific. For the albacore, on 

 the other hand, morphometric comparisons of fish from the eastern and 

 western north Pacific have, so far, failed to show significant differences, 

 and the recent recovery off Japan of a specimen tagged off California 

 tends to indicate that the North Pacific albacore may be a single large 

 population. Respecting skipjack, work in progress by the author in- 

 dicates that the skipjack of the region of the Eastern Pacific fishery are 

 probably morphometrically different from those of Oceania. This work 

 has, however, not been completed. So far as the tropical yellowfin and 

 skipjack tunas of the Eastern Pacific are concerned, then, there is evi- 

 dence to support the belief that they are distinct from those of the other 

 regions of the Pacific, so that a very intense fishery could reach the 

 point of overfishing. 



The very rapid growth of the Eastern Pacific fishery for these 

 species, and the very incomplete knowledge of their biology, ecology, 

 and life history, has caused concern that the fishery could become over- 

 developed, with consequent overfishing of the tuna stocks of this area. 

 Since most of the tuna catch is made by means of live bait, there has 

 also been concern lest the populations of bait fish be overfished with 

 disastrous effects on the yield of tuna. This situation, obviously, re- 

 quires that scientific investigations be conducted, in order to provide 

 an adequate foundation of knowledge of the biology and ecolog}' of 

 the fishes concerned, and of the effect on them of the increasingly in- 

 tense fishery. 



Although our knowledge of the ways of life of the tunas is small, 

 certain things we do know. We know that they are creatures of the 

 open sea, inhabiting the reaches of the ocean beyond the territorial 



