CHENG and SHULENBERGER: DISTRIBUTION AND ABUNDANCE OF HALOBATES 



carry the species westward (Sverdrup et al. 1942), 

 its range shows no such effect (Figures 2, 4). More 

 samples from the central equatorial Pacific are 

 needed to confirm the apparent abrupt termina- 

 tion of the species' range at about long. 112° W. In 

 the EASTROPAC area,//, sobrinus does not occur 

 west of about long. 112° W or south of lat. 5° S 

 (Figure 4). While the ranges of//, sobrinus and//. 

 micans overlap somewhat, their regions of high 

 population density (defined as samples with ^10 

 individuals) overlap very little (Figure 5). 



Halobates sericeus is clearly confined to the 

 central watermasses of the North and South 



Pacific. The three records of this species on the 

 Equator (at long. 82° W, 119° W, and 129° W; Figure 

 2) appear likely to be misidentifications (data from 

 Herring 1961). However, present data also include 

 one individual which lies well outside the appar- 

 ent range of the species (Figure 6; at long. 100° W, 

 lat. 16° N) and we have reconfirmed the identifica- 

 tion of this specimen. Since these insects are usu- 

 ally <4 mm long, individuals may be carried long 

 distances by the wind. This could explain such 

 isolated captures. Halobates sericeus does not 

 occur in the upwelling areas of the eastern tropical 

 Pacific, nor in the zonal equatorial currents (Fig- 



FlGURE 5.— Areas of high population densities of three Halobates species in the EASTROPAC area. "High" is defined as occurrence of 



A^^IO individuals in at least one sample (area per sampe =1,800 m^). 



585 



