As predictably as tourists flock to the famous beaches 

 of Waikiki in summer does the skipjack catch rise in the 

 warmer months. Both tourists and tunas are a source of 

 income to the State of Hawaii. (But tourism is a $200- 

 million-a-year business ; the fishing industry brings in about 

 $1 million to the fishermen.) The arrival of both tourists 

 and tunas in Hawaii is predictable. Unpredictable are the 

 numbers in which either will turn up. May 1965 was a 

 phenomenal month for the skipjack fleet. Ofl'icial figures 

 are not yet available, but it is no secret that in May the 

 fishermen had a month such as normally occurs only at the 

 peak of the season. July. In fact, this May's catch was 

 estimated to exceed that of most July's. Fishing almost 

 within sight of Waikiki, the sampans came home night 

 after night heavily loaded with aku. And the captains of 

 the Laboratory's research vessels reported that the fleet 

 was only nibbling on the population ; schools were abundant 

 offshore for many miles to sea. In June the catch slackened, 

 but Hawaii still appears to be headed for a record year. 



The unusual, catch in May could be attributed to two 

 causes. First, it may have represented the passage through 

 the fishery of a year-class of great strength. Year-classes 

 of almost legendary abundance are well documented in many 

 fisheries. Like comets and great men, they appear so briefly 

 and infrequently as to be remembered long afterward. The 

 much studied 1939 year-class of sardines off the west coast 

 provides an instance, as does the classical 1904 year-class 

 of Norwegian herring. Second, the May catch might have 

 reflected the response of the skipjack to some change in 

 the ocean environment. These two posibilities are not 

 mutually exclusive, of course. 



Aku Forecasts 



As has been mentioned, the Hawaiian Islands lie near 



the boundary between two water types. It is a boundary 



that, like the front line in a stalemated war, shifts back and 



forth. Thus the islands are bathed by water of relatively 



high salinity during part of the year, by less saline water 

 during the rest. Normally, but not always, the more saline 

 water prevails during the fall and winter, the less saline 

 during the late spring and summer. 



Good fishing seasons for skipjack tuna are often charac- 

 terized by a flow of less saline water about the islands. This 

 circumstance is interesting but of little predictive value to 

 the fishermen, for by the time the less saline waters arrive 

 off Hawaii's shores, the fish are there too. Our Laboratory 

 scientists have noted, however, what appears to be another 

 characteristic of good fishing years: the seasonal warming 

 of the sea surface starts early. 



Using the time of initial warming, as measured at Koko 

 Head, the southernmost point of the island of Oahu, and 

 information on the changes in salinity near the islands, 

 oceanographer Gunter Seckel for the past 6 years has 

 issued an "aku forecast" in April. The season has usually 

 borne out the forecast. The forecast for 1965 called for an 

 "average or above average" catch, and the fishery is un- 

 deniably headed that way. 



These forecasts are of more use to the scientists than 

 to the fisherman. "Below average," for example, a term 

 as exact as the scientists are yet prepared to use, could mean 

 anything from rather poor to catastrophic, a Ijig difference 

 to a man trying to make his living from the fishery. To 

 the scientists they provide clues to the natural jjrocesses 

 that may account for the variations in the skipjack catch, 

 and these clues are being followed up. 



The phenomenal catch in May provided a dramatic illus- 

 tration. The salinity value of ;M.8 ",,,, (parts per thousand) 

 has been empiiucally selected as that separating "favorable" 

 from "unfavorable" waters. Figure 12 shows that when 

 the salinity at Koko Head dropped below this value, and 

 stayed there, the estimated skipjack catch rose abruptly 

 and although landings declined in June, they remained well 

 above previous levels. The estimated monthly take of skip- 



16 



