NOURISHMENT OF CENTRAL PACIFIC STOCKS OF TUNA 139 



(log V + 0.1 sin t) where V^ is the adjusted volume, V the unadjusted 

 volume, and t the .angle of rotation of the hour hand on the 24-hour 

 clock at the time of the mid-point of the hauling period, with zero rota- 

 tional angle such that the angle whose sine is 1.0 occurs at midnight 

 and — 1.0 at noon. 



Figure 8. — Diagram of wind vectors, plankton abundance, a-nd tuna distribu- 

 tion in the equatorial zone. A. Resultant wind vectors were computed 

 as the weighted means of frequency and speed from the several compass 

 points for 5-degree squares bordering the equator as published in U.S. 

 Hydrogi^aphic Office Pilot Chai't for the North Pacific for August 1952, 

 the arrows point in the direction of travel and their shafts are pr-opor- 

 tional to the weighted mean speed. B. Mean plankton volumes at se- 

 veral longitudes computed as the mean of all hauls taken from between 

 latitudes 5°S to 10 °N at or near the given longitude. C. Distribution 

 of yellowfin tuna in the mid-Pacific equatorial region as estimated from 

 longline catches. The lightest stipling represents less than 3 yellowfin 

 tuna per hundred hooks, the heaviest represents more than 9 per hun- 

 dred hooks and the intennediate stipling represents intermediate catch- 

 ing rates. For orientation as to location and area there is given by 

 light stipling the area of the Japanese prewar longline fishery and by 

 dashed outline the area of the American west coast live bait and purse 

 seine fisheiy for yellowfin and skipjack tunas. 



