Table 2. — Concentrations of Pleuroncodes planipes, adults and juveniles {not larvae), in mlJlOhn} of water strained, on 



cruise TO-eJf-2 



> Series of night surface hauls with the large micronekton net near Uncle Sam Bank. 



chlorophyll a occurred together in the upwelling 

 or in recently upwelled water. 



The occurrences of tuna (both species) were on 

 the edges of the area of high concentration of red 

 crabs where surface temperatures were all between 

 22° and 18° C. No tuna were recorded in the large 

 inshore areas where red crabs were equally or more 

 abundant and temperatures were lower; the fish 

 probably avoided these areas. One 1° square, 

 bounded by lat. 26° and 27° N. and long. 114° and 

 115° W., had a significant amount of fishing effort 

 (six boat-days) tliat yielded no tuna in the month 

 of the cruise. According to figure 6, almost all of 

 this area was either colder than 20° C. or had less 

 than 40 ml./l,000 m.' of red crabs; it is not sur- 

 prising then that tuna were not found. Elsewhere, 

 in areas where no occurrences are shown in figure 

 6, the distribution of yellowfin and skipjack tunas 

 at the time of the cruise is not known. Tunas could 

 ha\-e occurred along other parts of the edge of the 

 cool, food-rich, water. 



Figure 6 shows an isolated occurrence of abim- 

 dant red crabs far offshore, where surface chloro- 

 phyll a was below 0.1 mg./m.' and tuna distribu- 

 tion unknown. Such offshore distributions, which 

 Boyd (1967) and Longhurst (1967) have reported 

 previously, may represent individuals that the 

 California Current has carried out of tlie coastal 

 region. 



CRUISE 6608 



This OalCOFI cruise, made in August 1966, 

 covered only part of the area of interest. The 



results represent conditions at a slightly later 

 stage in the year tlian those for cruise TO-64-2. 

 The CalCOFI stations have been given serial num- 

 bers as shown in figure 7. Figures 7 and 8 show 

 cruise coverage and distributions of properties. 

 The red crab data are given in table 3. 



The surface isotherms (fig. 8), especially 23° C, 

 show the same tonguelike distributions as before. 

 Cool tongues ran offshore from areas which lie 

 south of Point San Eugenio and Abreojos Point; 

 here a small inshore belt of upwelling or upwelled 

 water under 20° C. occurred. Warmer water lay on 

 both sides of these tongues. Surface temperatures 

 for the whole area were between 17° and 26° C. — 

 very close to the range (16°-25° C.) in an average 

 August (Anonymous, 1963). 



Concentrations of surface chlorophyll a ranged 

 from 2.0 to 0.03 mg./m.^, but those over 1.0 mg./ 

 m.^ were confined to a small inshore area between 

 Point San Eugenio and San Pablo Point. It was 

 not possible to draw an isogram for 0.1 mg./m.^ 

 with confidence, because observations were not 

 made in some parts of the area. In general, con- 

 centrations below 0.1 mg./m.^ were in water over 

 23° C, outside the main cool tongue shown in 

 figure 8, but some of them were in the small (east- 

 em) cool tongue as well. All concentrations above 

 0.2 were in the cooler water, as expected. They 

 are charted in figure 8 to show two areas, which 

 may, however, have been joined, because observa- 

 tions were not made between them. 



The sampling of red crabs on this cruise was 



DISTEIBUTION OP TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA 



161 



