AHLSTROM: KIND AND ABUNDANCE OF FISH LARVAE 



Table 5. — Summary of temperature differences within upper 50 m depth (differences in temperature at the surface 



and at two selected depths — 10 m and 50 m) summarized by quadrants. 



tered between lat 15° and 20°N. Temperatures 

 at 10 m were usually the same as at the surface, 

 and in only one instance was the difference as 

 great as 1.3 °C. Temperatures at 50 m were 

 identical to, or within 1°C of, the surface tem- 

 peratures at about 20 9r of the stations, all lo- 

 cated between lat 2° and 10°N — these were sta- 

 tions with deep thermoclines. Temperature 

 differences between the surface and 50 m ex- 

 ceeded 5°C at about 35% of the stations. 



EQUATOR, LAT 2oN TO 2oS 



Surface temperatures were variable, with 

 9.5°C range (16.4° to 25.9°C). Lowest surface 

 temperatures, undoubtedly resulting from up- 

 welling, were encountered seaward of the Ga- 

 lapagos Islands, between long 92° and 98°W, 

 lat 0.5°N to 2.0°S, but cold water was also en- 

 countered farther offshore. Thermoclines were 

 shallow at most stations inshore from the Galap- 

 agos Islands, the difference between surface and 

 50 m exceeded 5°C at about 63% of the stations, 

 but the surface water was warmer than offshore. 



SOUTHEAST QUADRANT, EXCEPT 

 WITHIN 2° LATITUDE OF EQUATOR 



Water temperatures were much lower in this 

 quadrant than in the northeast quadrant. Few 



surface temperatures were as high as 20 °C, and 

 the average surface temperature was 18.7°C. 

 The thermocline was usually deep. At 65% of 

 the stations the temperature at 50 m was the 

 same as that at the surface or was not more 

 than 1°C colder. 



SOUTHWEST QUADRANT, EXCEPT 

 WITHIN 2o LATITUDE OF EQUATOR 



Surface temperatures ranged from 20.6° to 

 24.9°C (average 21.0°C), Temperatures at 

 10 m were usually the same as that at surface 

 or within 0.5°C. Temperatures at 50 m were 

 identical to the surface at 30% of stations and 

 within 1°C of the surface temperature at 80% 

 of stations, indicative of a region of deep ther- 

 mocline. 



In summary, water temperatures were much 

 higher north of the equator, than south of the 

 equator. Surface temperatures averaged 8.5 °C 

 higher in the northeast quadrant than in the 

 southeast quadrant. Offshore the differences 

 were almost as great; surface temperatures 

 averaged 6.6°C higher in the northwest quad- 

 rant than in the southwest quadrant. 



As noted in the paper dealing with ETP I col- 

 lections, information is mostly lacking on depth 

 distribution of fish larvae in the eastern trop- 

 ical Pacific. Because of the marked variation 

 in depth of thermocline encountered in different 



1159 



