Central Pacific Salpidae — Yount 
117 
each of the meridional series of salp samples. 
It should be pointed out, however, that the 
distribution of the other determined factors— 
density, salinity, inorganic phosphates, and 
dissolved oxygen — is very similar on all meri- 
dians studied here (see Cromwell, 1954). The 
detailed descriptions of all parameters studied 
may be found in Cromwell (1953, 1954). 
Considering the emphasis to be placed on 
temperature, it is desirable to describe its 
major variations. It was found (Cromwell, 
1954) that temperature distribution in the 
North Equatorial Current was characterized 
by a relatively poorly developed thermocline. 
The region of the Counter Current (about 8° 
N. to 4° N.) was characterized by a gradual 
north-south sharpening of the thermocline 
and a deepening of this layer to the south. 
The northern part of the South Equatorial 
Current was characterized by a well- developed, 
deep thermocline in the region of upwelling. 
South of this region, the thermocline again 
became less well defined. Inspection of the 
temperature distribution (Cromwell, 1954, fig. 
6) shows conical isotherms resulting from an 
upward transport of the cooler waters of the 
lower surface layer and upper thermocline 
from 1° N. to 2° S. This is associated with the 
wind-induced divergence and the attendant 
upwelling, as evidenced by the cooler tem- 
perature found at the surface. 
As the histograms in Figures 3 to 6 show, 
the salps discussed herein were taken on two 
meridional sections during cruises 5 and 8 of 
the "Hugh M. Smith." The histograms show 
the observed variation of the total salp vol- 
ume, total salp numbers, and the numbers of 
the commonest species, Thalia democratic a, 
Salpa fusiformis , Kitteriella amhoinensis , and Cy- 
closalpa pinnata. A typical section, cruise 5, 
158° W., is discussed in detail and the re- 
maining sections are compared with it. 
The typical section (Fig. 3) shows that the 
majority of the relatively large volumes were 
taken from 1° S. to 4° N., in or near the region 
of upwelling which was characterized by low 
temperature and a high phosphate value. Large 
volumes were also taken from 17° to 21° N., 
apparently due to the influence of the Ha- 
waiian Islands. 
Total numbers of salps (Fig. 3 a) showed a 
very different distribution from that of total 
volume, as can be expected, since a few large 
specimens may greatly influence volume but 
not numbers. Inasmuch as Thalia democratica 
comprised the principal portion of the total 
numbers at most stations, it is discussed 
simultaneously with total numbers. The great- 
est numbers were taken in the region under 
influence of the upwelled waters but large 
numbers were also taken in waters far from 
this region (15°N.), a fact which may be 
explained by the presence of a current shear 
and/or eddies associated with the Hawaiian 
Islands. The large numbers taken at 4°, 5°, 
and 9° N. appear to be associated with the 
shearing effect at the southern and northern 
boundaries of the Counter Current. The 
majority of the small numbers occurred 
away from the upwelled region, in regions 
where the previously described layered system 
was well developed and the phosphates in 
the euphotic zone were low. 
The other common species show a rather 
different distribution (Fig. 3 b). Salpa fusi- 
formis was most abundant near the region of 
upwelling. No substantial influence was 
shown by proximity to islands. Kitteriella 
amhoinensis was taken in greatest numbers 
near the upwelling and in regions possibly 
influenced by proximity to islands. Cyclosalpa 
pinnata occurred only in small numbers; never- 
theless, its principal occurrence was in the 
region of upwelling in the South Equatorial 
Current. It does not appear to have been in- 
fluenced by other factors examined. 
The section of cruise 5, 172° W. (Fig. 4), 
is characterized by a more general meridional 
Fig. 2. "Hugh M. Smith,” cruise 8; January-March, 1951. Numbers 1-106 indicate stations at which plankton 
tows and hydrographic observations were made. The underlined numbers represent stations examined for the 
present study. (After Cromwell, 1954.) 
