Figure 4. — Distribution of catch per unit effort of skipjack tuna taken by the Japanese tuna longline fishery, 1964. The contour lines are 

 drawn at intervals of 2, 4, 8, 16, etc., times the mean catch per 1,000 hooks per quarter per 5° area fished. The symbols + and — 

 represent CPUEs less than twice the mean and no skipjack tuna caught or recorded, respectively. (The small circles are contour lines, not 



