FISHERY BULLETIN: VOL. 72. NO. 1 



eutrophic equatorial latitudes but may typically 

 extend through 200 m or more in the oligo- 

 trophic subtropics must now be viewed within 

 the comi)lexity of thi-ee tropical and one tropical- 

 subtropical species. In this context, vertical dis- 

 tribution api^ears to differ among the species: 

 i.e., phiniata probably has a deeper range than 

 its three tropical congeners. Confirmation re- 

 quires analysis of vertically stratified sampling 

 from regions supporting pUintata and one or 

 more of its cognates. 



Abundance 



Interest in patterns of geographical distribu- 

 tion relative to phylogenetic affinities among 

 the species prompted us to make preliminary 

 comparisons of abundance among the species of 

 PontelUua. For the analysis we selected sets 

 of similarly collected, quasi-synoptic, quantita- 

 tive samples that represented the epijjelagic 

 layer between 150 m or 200 m and the surface. 

 The sets of samples comprise transects crossing 

 the equator at different longitudes in the Pacific 

 Ocean (Figure lb. Table 14). Only adults were 

 tabulated, the mesh width of the i)lankton nets 

 usually being too large (~0.5 mm) to retain 

 younger copepodids (Table 15). The hour of 

 sami)ling was ignored in the absence of appre- 

 ciable differences in either frequency of occur- 

 rence or mean abundance of PontelUua between 

 samples collected at day or night (Tables 16, 17). 



The mean abundance of species of PonteUina 

 ranged from 0.01 to 0.9 per m^ (Figure 35). 

 Abundance in the Pacific followed a generally 

 familiar pattern. Higher values api:)ear in the 

 eastern third of the Pacific as well as in the 

 Austral-Asian seas and the Indian Ocean while 

 lower values predominate in the middle and 

 western Pacific (Figure 35). 



The three species, P. plumafa, morii, and 

 .so6r///fl, tend to vary independently in abundance. 

 Mean abundance and frequency of occurrence 

 values from the Indian Ocean and Austral- 

 Asian seas are similar for morii and plumata, 

 though evidence of finer-scale geographical 

 differences sejiarating the two si)ecies within 

 the Indian Ocean have been noted (Figure 38). 

 Eastward across the Pacific the abundance and 

 occurrence of plnmafa persist or even increase 

 \x\) to but not beyond the boundary of the eastern 

 tropical Pacific where sobriiia predominates. 



P. morii differs from plumata by showing a 

 sharp decrease in abundance across the entire 

 Pacific Ocean. However, high numbers of morii 

 were found between 10 m and the surface south 

 of the equator along long. 92 ''W. This is too 

 distant for direct transport from the main 

 area of abundance in the Indian Ocean and 

 Austral-Asian seas; the unusually high values 

 for morii, 1.96 per m'' at lat. 4°16'S and 0.16 

 per m-' at lat. 12°19'S, suggest recruitment by 

 local reproduction. 



Table 13. — Occurrence of Ponicllinu by sampling depths at selected stations of 

 the Carnegie cruise VII (Wilson, 1942). Analysis limited to Carnegie stations 

 providing abundance estimates from all three sampling depths. Grouping of the 

 stations under a particular species or combination of species determined by its 

 geographical origin relative to the distribution of species of PonteUina determined 

 by the present study. Values are the sums of numerical equivalents of Wilson's 

 index for PonteUina abundance divided by the number of stations in the geograph- 

 ical group. Index equivalents are: 1 = 1-5 specimens (trace); 2 = 6-10 specimens 

 (rare); 3 = 11-24 specimens (frequent); 4 = 25-50 specimens (common); 5 = >50 

 specimens (abundant). 



Probable 

 dominanf 

 species 



Sum of obundonc e 

 No. stations 



m 50 m 1 00 



Carnegie station 

 numbers 



sohrina 



morii 



plumaia-morii 



pliimata-platy chela 



plumalu 



2.66 0.33 1.33 35,37,38 



L83 0.0 0.50 40,41,43-45,48 



1.05 1.11 0.83 98, 99, 101, 103-108, 151, 153-160. 



LOO 1.33 0.67 22,23,27,31,32,34 



0.50 0.67 0.50 16, 18, 49-52, 56, 57, 67, 79, 94, 96, 97, 



109,112,132,133,135,136,139,140,142, 



145, 149 



106 



