Table U. — Piatlos given In table 3 that Indicate probable effects of the front on the 



distribution of animals 



Type of ratio 



Group of organisms 



Type of net haul 



High value on warm side as 

 compared with middle and 

 cool side 



High value in middle as com- 

 pared with either side 



High value on cool side as 

 compared with middle and 

 warm side 



Low values in middle as com- 

 pared with either side 



Red crab larvae 



Red crab adults 



Pandalid shrimps 



Chaetognaths (marginal). 



Euphausiids. . . 



Pteropods 



Copepods 1 

 Chaetognaths / 



Stomatopod larvae 



Pteropods 



Copepods 



Euphausiids 



Siphonophores 



Chaetognaths 

 Fish 



C-B (in thermocline) 

 1.52- by 1.52-m. nelfton net 

 1.52- by 1.52-m. nekton net 

 Oblique tows, A series 



Oblique tows, A and F series 

 Oblique tows, A series 

 (Oblique tows, F series 

 \ and C-B ( above thermocline) 



1.52- by 1.52-m. nekton net 

 Horizontal surface tows 



C-B (in thermocline) 



1.52- by 1.52-m. nekton net 



the strong environmental gradients that con- 

 stitute the front (assuming all forms are 

 equally aggregated). 



On the whole, the cool side contributes more 

 to the total plankton of the area than does the 

 warm side,^ though a marked maximum of a 

 plankton component in the middle is comnnonly 

 found. The outstanding exception to this is in 

 the results of the surface net tows (if we ignore 

 the chaetognath component), which strongly 

 reflect the greater contribution of the cooler 

 side. There may be an explanation for this: 

 although they are marked, the horizontal prop- 

 erty gradients at the surface are weaker than 

 the vertical property gradients at greater 

 depths (e.g., 30-60 m.); in other words, the 

 effect of the front may be much less marked 

 at the surface than at depth. 



This explanation is not borne out by the re- 

 sults of the C-B tows which, however unfav- 

 orably C-B samplers may compare with other 

 nets, can be compared satisfactorily with each 

 other. Catches above the thermocline show 

 nnarked aggregation in the middle (especially 

 of copepods and chaetognaths); those in the 

 thermocline show a much more general distri- 

 bution of zooplankton. 



To sum up: the data do not allow specific 

 statements about the effect of the front on the 

 biota, though they do support the aggregation 

 hypothesis. Although, on the whole, micro- 

 nekton does not congregate in the middle of 

 the front, some of the results (see table 3, 



Integration of the chlorophyll a. depth curves in figure 

 30 shows that probably there is most chlorophyll a on the 

 cool side too. 



F series of oblique tows, red-crab component) 

 suggest that it might do so occasionally. 



Miscellaneous observations . --Incidental to 

 all the special observations, we observed the 

 general abundance of sea life, as well as sea 

 and weather conditions. The sea was calmer 

 north of a line bearing about 100° - 280° from 

 Cape Falso than to the south of it; as the vessel 

 went south the sea became steadily and quickly 

 choppier, and the wind increased. This change 

 was not great, however, and was the result of 

 moving from the shelter of the land into the 

 prevailing northwest wind, and was only par- 

 tially related to the front itself. Marlin were 

 particularly abundant here, and several sport- 

 fishing boats caught marlin frequently in the 

 calm water. Some turtles were observed, 

 though turtles were more abundant further 

 south; we saw them on the passage from Tres 

 Marias Islands to Cape San Lucas. Sea birds 

 were not abundant. We saw no tuna boats or 

 schools of tuna during the period of study, 

 but often took black skipjack on jigs at this 

 front, and tuna boats were active and success- 

 ful in the general area at that time (Griffiths, 

 1963). 



The weather and sea conditions changed 

 relatively little during the period of study ex- 

 cept as noted; cloud cover and haze prevented 

 star sights and often made it difficult to get 

 good bearings. 



The calm weather and the front's stability 

 made observation of the front easy. This is in 

 contrast to the fronts studied on cruise TO-60- 

 1, except front 3; observations on these fronts 

 are presented below. 



41 



