Table 2. — Results of net hauls made at the Cape San Lucas Front (front 5) — Continued 



Station 



Time 



of 



day 



Depth 



of tow 



(m. ) 



Volume 

 plankton 

 ml. per 

 lO^m.^ 



Ratio 



of 

 volvmies 



Volume 



mif;ronekton 



'.ml. perlO^m.^ 



Ratio 



of 

 volumes 



Dominant forms 

 (by volume or number) 



Zooplanirton 



Micronekton-' 



HORIZONTAL CLARKE-BUMP US NET HAULS (con. 

 ii) IN the thermocline 



OBLIQUE 5-ft. NEKTON NET HAULS 



w = warm side: m = middle ; c = cool side of front. 



n = night; d = dusk. 



Micronekton is, roughly speaking, a small organism of minimum linear dimension 5 cm. and of 

 maximum linear dimension of, say, 15 cm. 



^ Excludes zooplankton component; see footnote to table 3. 



the middle according to the F series of oblique 

 hauls than the corresponding amounts accord- 

 ing to the A series of oblique tows made on the 

 previous night (see tables 3 and 4, and text 

 below). The chaetognaths in these same hauls 



seem to have accumulated even more rapidly 

 than the copepods and euphausiids in the lapse 

 between the A series of hauls and the F series. 

 The following table summarizes the points 

 just mentioned. 



(A series) Oblique tows 



Organisms: (w) (m) (c) 



Copepods 1.0 1.7 0.8 



Euphausiids ... 1.0 7.9 4.0 



Chaetognaths,. 1.0 0.5 0.4 



This marked accumulation may also have 

 happened to the chaetognaths and copepods in 

 the surface waters (compare results of surface 

 tows with those of the C-B tows above the 

 thermocline, in table 3, bearing in mind the 

 real linnitations of the results obtained by C-B 

 samplers ). 



Disregarding the plankton component of the 

 1,52- by 1.52-m, net hauls, the abundance of 

 micronekton in the middle of the front is, on 

 the average, about the same as that on the 

 warm side and about half as great as that on 

 the cool side (on the average, the cool side has 



( F series ) 



(w) (m) (c) 



1.0 5,6 2,2 



1.0 11,0 2,5 



1,0 4,5 2,6 



the most zooplankton). This information is 

 derived from table 3 by omitting the euphausiid 

 and stomatopod entries in the nekton data and 

 recalculating the average values; whereupon 

 the values 1,0:11,2:12,1 become 1.0:0.9:1.7, 



There are two possible causes of the various 

 relative abundances of component groups in the 

 front, apart from effects of mechanical aggre- 

 gation and predation: (1) in situ production of 

 some groups is higher than for some others in 

 different parts of the frontal system, and 

 (2) some forms experience a relatively higher 

 death rate than others when confronted with 



39 



