of tuna into this layer. It is thought that yellow- 

 fin are especially sensitive to decreased oxygen 

 pressure, and even under normal conditions are 

 near the upper threshold of oxygen utilization. 

 This latter hypothesis is based on a lowrecovery 

 rate for yellowfin tagged and released in very 

 warm waters. It h a s been hypothesized that 

 larval tuna entering the thermocline layer suffer 

 a high mortality due to low temperatures or lack 

 of oxygen. Another explanation could be a re- 

 duced growth rate, with a subsequent increase 

 in length of larval life and prolonged exposure 

 to the hazards of larval life. Whether or not 

 larval tuna have sufficient energy to overcome 

 the marked change in density at the surface 

 layer-thermocline interface should be consid- 

 ered as a factor limiting their vertical distri- 

 bution. Considerable evidence from larval tuna 

 collections indicates that most larvae are found 

 above the thermocline. 



One of the objects, but not the only one, 

 of studies of oceanography as related to tuna is 

 to be able to predict the amount of tuna available 

 to commercial fishermen in a particular locality 

 and at a particular time. While studies have not 

 progressed to the extent that this objective can 

 be fully realized, prediction techniques have 

 been developed and are in use. 



In studying the availability of albacore to 

 the Oregon and Washington fishery (latitudes 40° 

 to 50° N. , and west from the coast to longitude 

 130° W.) it was found that above average catches 

 were associated with above average August sea 

 surface temperatures . Similarly, below average 

 catches were made during years with below aver- 

 age temperatures for August. Further studies 

 suggested that the August sea surface tempera- 

 ture, and thus the potential availability of alba- 

 core, could be predicted from a consideration 

 of the temperature anomaly during May and June 

 (the amount by which the monthly temperatures 

 for the individual year differed from a 12 -year 

 monthly average). It is pertinent to note that 

 in at least one instance when the August 

 temperature -total catch relationship failed to 

 develop, 1957, it is likely that the low catch was 

 due, at least in part, to economic conditions 

 rather than to a lack of fish. 



It has been hypothesized that albacore 

 available to the Japanese winter longline fishery 

 make a vertical migration in the spring and be- 

 come available to the Japanese summer live- 

 bait fishery. Horizontal distribution of tempera- 

 ture of the surface waters during the winter 

 appears to affect the migration of albacore from 

 the longline fishery into the pole -and -line fishery. 

 The variations and persistence of warm and cool 



water, winter to summer, together with the lo- 

 cation of the winter longline fishery, appear to 

 form a basis for predicting the location and 

 abundance of albacore available to the summer 

 live -bait fishery. 



During some years in an area south of 

 Japan (latitude 28° to 36° N., longitude 135° to 

 140° E.), cold inshore waters intruding from the 

 north force the winter fishery to operate in the 

 eastern and southern portions of the area. This 

 cold water also forces the spring migration of 

 albacore into an easterly and southerly direction, 

 and as a result the fish are available to the fish- 

 ery for only a short period of time, and catches 

 tend to be below average. In other years, when 

 warm water is adjacent to the coast, the winter 

 fishery develops close to land, and the spring 

 migration moves through the western and north- 

 ern portions of the area. As a result albacore 

 remain available to the pole -and -line fishery for 

 an extended period of time. A third situation in 

 which the relative persistence of winter condi- 

 tions may be used to predict the success of the 

 summer fishery involves a combination of the 

 two situations described above. 



In the area east of Japan (latitude 30° to 

 40° N. , longitude 140° to 160° E.), a successful 

 summer live-bait fishery depends upon the ab- 

 sence of cold water inshore and the formation of 

 multiple pools of albacore in the winter longline 

 fishery. When these fish migrate to form a sin- 

 gle large aggregation in the western portion of 

 the area, a good fishery is likely to develop. The 

 catch from the live -bait fishery is likely to be 

 small when cold water is present in inshore 

 areas, when the winter aggregations of albacore 

 are in the eastern portion of the area, and if the 

 fish do not form a single aggregation in the 

 spring. 



From these descriptions it can be seen 

 that in both the southern and eastern Japanese 

 fisheries a knowledge of winter temperature 

 patterns and winter fish distribution provides a 

 predictive technique for evaluation of the degree 

 of success which may be expected in the summer 

 live -bait fishery. 



The magnitude of the annual catch made 

 by the Hawaiian live -bait skipjack fishery has 

 been shown to be related to the time of the late 

 winter reversal from cooling to warming of the 

 surface waters in the area of the fishery . It was 

 observed that when the time of first warming 

 occurred during February or earlier a better 

 than average skipjack catch in the Hawaiian fish- 

 ery could be expected. When the warming oc- 

 curred in March a poor catch could be expected. 



