night, how long a school lasts as a school (some scientists 

 believe it may be throughout the lives of the fish) , the 

 routes they travel in the central Pacific — all this informa- 

 tion, and more, will become available. To date most of 

 the work has been done on schools in Hawaiian waters, 

 as the operators have familiarized themselves with the 

 equipment. 



The scientists are using the sonar not only as active 

 equipment but also as passive. In this mode, they listen 

 for a special sound transmitter that is attached (or fed) 

 to a fish (fig. 13). The tag now being used experimentally 

 is 3 inches long and 1 inch in diameter. It broadcasts a 

 sound pulse every second. To date, scientists have used 

 the sonic tag on individual (i.e., nonschooling) tunas and 

 sharks. They were able to track one shark for 18 hours, 

 the tunas for shorter periods. They hope that further 

 development of the sonic tag will enable them to track 

 tuna schools through the depths for longer periods of time. 



By determining the behavior of individual tunas and of 

 tuna schools in Hawaii waters, the scientists expect to gain 

 information that will allow them to design specialized gear 

 to make possible the development of this great potential 

 resource, according to Heeny S. H. Yuen, who heads the 

 sonar project. 



Skipjack Tuna Subpopulations 



In January 1968, Kazuo Fujino of the Laboratory in 

 Honolulu spent 2 weeks fishing for tuna in Tahiti. His 

 object was not food or sport, but to fill small plastic vials 

 with blood drawn from the fish he caught. Fujino is a 

 scienti-st whose specialty is the population genetics of 

 marine animals, particularly the tunas, and blood samples 

 afford .some of the data he needs. 



Tuna abound in Tahitian waters. Laboratory research 

 cruises in the 1950's found many schools in the Society and 

 nearby Marquesas Islands. Skipjack tuna are particularly 



plentiful. It was the skipjack tuna that Fujino flew 2,500 

 miles to study, for one large gap in scientific knowledge 

 of the skipjack tuna concerns the precise relation of the 

 fish of the central South Pacific to those elsewhere. 



History provides incontrovertible proof that man can 

 essentially wipe out a wild species. The buffalo is a spec- 

 tacular example, as is also the largest of all living creatures, 

 the blue whale. If the animal species of the sea are to be 

 used wisely, they must not be so heavily harvested that 

 they cannot reproduce themselves. In even an elementary 

 economy, the farmer saves seed grain, the rancher does 

 not .slaughter all his breeding animals; in the as yet 

 I)rimitive economy of the sea, which is based on hunting, 

 a fishery might risk devastating all of a species, or all of 

 a species in a certain area, if it is not carefully managed. 



Therefore scientists consider it essential to understand 

 the relation of the fishes in one area of the ocean to those 

 in another. Is there a single great skipjack tuna population 

 in the Pacific Ocean, for example, so that if catches were in- 

 creased in the central Pacific there would be enough of 

 the stock left elsewhere to replenish that area? Or are 

 there several smaller populations, or subpopulations, that 

 do not interbreed? 



The discipline of population genetics provides some leads 

 to the answers to these questions. Population genetics de- 

 pends upon the fact that certain characteristics are con- 

 veyed from one generation to the next according to rather 

 well-understood laws. In fishes, as in many other animals, 

 some of these characteristics are blood types and the 

 presence of certain proteins in the serum. 



Since it deals with populations, this branch of genetics 

 requires large numbers of samples. The blood type of a 

 single fish or a few dozen fish tells little or nothing about 

 the population as a whole. But when hundreds of fish are 

 sampled, the geneticist can draw valid conclusions about 

 the population. The reason is that isolated subpopulations, 



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