28 FISH AND GAME COMMISSION 



underwent an exceptional increase to parallel the expansion in purse 

 seine operations. Bonito landings increased from less than 1,000,000 

 pounds in 1944 to over 13,000,000 in 1947 (see Table 5). 



The picture outlined above intimates that the tuna fishery faces a 

 period of intensive exploitation. The future of the local industry depends 

 entirel}' upon the size of the avaihible stocks of tuna. If these stocks are 

 extensive and relatively untapped, then a healthy expansion is possible. 

 If, on the contrary, the stocks are limited in extent, and already heavily 

 fished, then further expansion is not warranted, and may precipitate 

 hardship and even disaster. 



The staff of the bureau foresaw this crisis ; and the entire investi- 

 jrative program was originally designed to answer this major question. 

 Unfortunately, the war brought the tuna investigation to a standstill, and 

 it was not resumed until the summer of 1946. 



Four species contribute to the pack of ''tuna." Of these, the bluefin 

 tuna and the albacore are temperate and seasonal fisheries. Because they 

 are seasonal, the catch of either species is determined b}^ the extent to 

 which they enter our fishing area, their abundance at that season, and 

 the length of time they remain available. Over an ll-j'ear period, the 

 combined catch of these two species has averaged less than 15 percent 

 of the total take of tuna. The remaining 85 percent has been supplied by 

 the other two species, namely, the sub-tropical and tropical yellowfin 

 tuna and skipjack. On the average the yellowfin supplies about 62 percent 

 and the skipjack 23 percent of tlie total catch of tuna. Because of this 

 fact, the laboratory investigations ccmcern primarily the yellowfin and 

 skipjack, with the emphasis upon the former. 



In order to determine the potential catch of yellowfin tuna, it is 

 necessary to know the extent of the stock supplying that catch. The work 

 interrupted by the war has been resumed, and it has been shown tenta- 

 tively in this biennium that the stock of yellowfin exploited by our fleet 

 is confined to the eastern Pacific, and is not replenished from the Central 

 Pacific Basin. Moreover, there are strong suggestions in as yet uncom- 

 pleted work that the catch per boat has already passed its peak. The 

 indications are, therefore, that the stock of yellowfin now exploited by 

 our fleet will not support indefinitely any appreciable further expansion. 

 The main emphasis of the entire tuna investigation is, therefore, con- 

 centrating upon an attempt to substantiate these indications, and deter- 

 mine definitely at what level the yellowfin fisherj' should be stabilized. 

 If the pack of tuna is to be substantially and permanently increased, it 

 must be at the expense of either : 



(1) A distinct and more distant stock of yellowfin and skipjack, or 



(2) The bluefin and albacore populations. 



Before the latter alternative can be accomplished, it will obviously 

 be necessary to locate these two species in those seasons when they are 

 not now available in our fishing areas. So the secondary and minor phase 

 of the tuna investigation consists now of exploratory work for bluefin 

 and albacore, and a determination of the extent of their populations. 

 In order to investigate vertical as well as horizontal extent, a set of drift 

 gill nets of varying mesh was ordered and delivered at the close of this 

 biennium; and the exploratory work has since begun. 



