204 OCEANOGRAPHY 



tepee, the progress of these 10 years has really been in the nature of a recon- 

 naisance, which has given us a better understanding of what we need to study. 

 Despite the excellent work which is being done by the scientists of several in- 

 stitutions and agencies in a very well coordinated way and on a scale which 10 

 years ago would have looked large, we are only on the threshold of unlocking the 

 secrets of the ocean which we can use to lower the cost per ton of catching tuna. 

 Some of the problems ahead of us are these : 



1. Skipjack 



As noted above, skipjack are far the most abundant tuna not only in our area 

 of ocean but probably in the world ocean. Yet they move out of the area of our 

 fishery into the open Pacific when, or before, they are the most desirable size for 

 canning. Where they go to is not known except that it is probably somewhere in 

 the area between 5° and 30° N. latitude, and between the mainland and the 

 Hawaiian Islands. 



In this area, as big as the United States, they must congregate in catchable 

 schools in relation to some oceanographic features such as along ocean "fronts," 

 or at the interface l)etween currents. But the detailed oceanography of the 

 region is so iioorly known that for a fisherman to sail blindly around in the 

 area looking for concentrations of skipjack simply is not economically feasible. 

 Yet within 10 years, certainly, the U.S. market will be requiring more tuna than 

 the limited yellowfin resource will provide on a sustained yield basis. 



2. Blue fin 



Bluefin tuna occur even closer to home than do skipjack, and we know even 

 less aliout them than we do about .'-kipjack. In season they come in close to 

 land in the area between Guadalupe Island (off northern Mexico) and the 

 Channel Islands (off southern California). In some years considerable catches 

 are made a stone's throw outside the coastal kelp beds. 



Where they come from or to where they return no one knows. There is no 

 reasonably accurate estimate of the size of the stock. That they do not spawn 

 in the adjacent ocean is known from the very extensive plankton hauls the Cali- 

 fornia cooperative fishery investigation has made over the past 10 years in the 

 area of the fishery and far to sea both north, south, and west of that area. All 

 we really know is that they show up and catches of 2,000 to 15,000 tons are 

 made during the season, which may be short or stretch over several months. 



3. Ocean ''fronts" 



Ocean "fronts" or "tide rips" are known to occur widely through the whole 

 area of our fishery and far out to sea beyond that. In some places they occur 

 with more frequency and ccmsistency than others. One might say that some 

 areas of the ocean are more "prone" to fronts than others. 



Fronts are areas where there is sharp turbulence and temperature change 

 across a narrow line that may be short or run unbroken over the horizon. The 

 front may last minutes, or hours, or perhaps much longer. Along the turbulent 

 front sealife gathers, the plankton brought in involuntarily by the currents 

 and the larger animals, including tuna, congregate because of this ; that is their 

 food. 



Fronts may very well be the secret of where the skipjack in our area congregate 

 far out to sea. But as little is known about the occurrence and location of 

 fronts as about the habits or whereabouts of the skipjack. 



Jf. ReJatimi of tuna to water nias-sn^ 



The Hawaiian Islands are at the edge of the normal mixing areas of two 

 large water masses of somewhat different origin. There is a large gyral that 

 swings down in clockwise manner from the western North Pacific extension 

 of the Kuroshiwo. The rest of that current goes on across the ocean to hit the 

 continent and then swing down south and out to sea again north of the equator 

 jr- n broiid slow-moving mass where it is known as the Cnlifornia current ex- 

 tension. When it reaches the longitude of the Hawaiian Islands its water is 

 somewhat less saline than that of the western Pacific gyral, but not much. Also 

 tiierc are subtle but delei-table differences in the temperatures of the two water 

 masses. 



The measurements that we use to tell these two water masses apart are so 

 small and subtle that it scarcely is credible that the skipjack should be re- 

 spondiuii to those differences. Yet the big oceanic skipjack are mostly in the 

 water mass of the California current extension and in years when that cuirent 

 is strong and comes into the Hawaiian Islands broadly the summer season skip- 



