CRUISE TO -64-1 

 JUNE 1964 



CAPE 



SAN 



LUCAS, 



\ir 



 YELLOWFIN TUNA 



A SKIPJACK TUNA 



• BOTH TUNA SPP. 



SURFACE TEMPERATURE, °C. 



null REOCRAB, >40ML./10^M.^ 



SURFACE CHLOROPHYLL, > 1 .0 MG./M.^ 



Figure 4. — Distributions of surface temperature, surface chlorophyll a, and red crabs for cruise TO-6-1-1 



and locations of contemporaneous tuna catches. 



2r 



N. 



27» 



26* 



25* 



\2f 



2f 



Baja California, and the other (both species) in 

 and northwestward of the warm offshore tongue. 

 Neither of tliese groups of tuna was in tlie area 

 of highest concentration of food, although the 

 second group reached the edge of it. In the front 

 area virtually no red crabs were caught in three 

 standard night micronekton hauls, and concen- 

 trations of all animals in these hauls (i.e., all poten- 

 tial tuna prey) ranged only from 9 to 16 

 ml./l,000 m.^ In the other tuna area concentra- 

 tions of red crabs were 7 and 46 ml./l,00(J m.^ at 



stations 29 and 48, and concentrations of all other 

 micronekton were 14 and 10 ml./l,000 m.^ Some of 

 the tuna aggregations in each of these areas were 

 only about 25 nautical miles (46 km.) from a much 

 richer food supply (over 100 ml./l,000 m.' of red 

 crabs — e.g., at station 52), but the fish would have 

 had to encounter temperatures below 17° C to 

 reacli it. Figure 4 shows that the tunas will tolerate 

 17° C. and suggests that lower temperatures are 

 not acceptable. 



A reasonable interpretation of figure 4 is that 



DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA 



157 



