'■■ " FEB .<^ 



"S5.. y-'^ 



Figure 10. --Location of 21° and 28° isotherms in the eastern Pacific according to Wyrtki 

 (in press). Blackburn (1962) has suggested that the distribution of skipjack harvested 

 along the coasts of the Americas is coincident with surface temperatures between 21° and 

 28° centigrade. 



northern and southern contingents is a function 

 of the north-south and temporal distribution of 

 eastward-moving skipjack as these fish encoun- 

 ter the splitting mechanisms. One possible split- 

 ting mechanism is the warm water cell (surface 

 temperature greater than 28° C.) in the vicinity 

 of lat. 15° N. off the coast of Central America. 

 The location of this warm water cell for average 

 conditions is contained in Wyrtki's^ recent 

 paper (see fig. 10) and has been discussed by 

 Blackburn (1962: p. 39-40), who suggested that 



it impedes north-south movement of skipjack 

 across lat. 15° N. to an extent which varies with 

 surface temperature. This is undoubtedly the 

 case, but it appears that the cell has a more 

 important effect; it is one of the mechanisms 

 that serve to split skipjack into northern and 

 southern groups. 



A/ Wyrtki, Klaus. Thermal structure of 

 eastern Pacific Ocean. Deut. Hydrograph. Z. 

 press . ) 



the 

 (In 



14 



