Table 5. --Seasonal variation in the distribution of Sagitta elegans and Eukrohnia hamata 

 with associated surface temperatures and salinities 



Transition Zones by the Hugh M. Smith, the 

 Mitkof, and the Paragon (fig. 6), In the fall on 

 Charles H. Gilbert cruises 17 and 23 (fig. 6) 

 they were taken in the Transition and Subtropic 

 Zones, and in winter on Hugh M. Smith cruise 

 27 (fig. 6) they were taken in the Subtropic Zone 

 near its northern boundary. It has been noted 

 that the albacore are distributed in respect to 

 certain isothernns and are not restricted to 

 any one current or water mass (Shomura and 

 Otsu 1956, Graham 1957); insofar as the chae- 

 tognath zones are concerned the albacore seem 

 to shift from the Subarctic Zone in summer 

 southward to the Subtropic Zone in winter, and 

 are not distributed in respect to particular 

 water types or plankton complexes. 



SUMMARY AND CONCLUSIONS 



1. On Hugh M. Snnith cruise 30 larger catches, 

 as number per unit of water strained, of 

 chaetognaths and pteropods were taken in 



the shallow (0 - 40 m. ) hauls than in the 

 deeper (0- 140 m. ) hauls both during the day 

 and at night. The chaetognaths occurred in 

 greatest abundance in the Subtropic Zone; 

 the pteropods were an important constituent 

 of the plankton in both the Subtropic and the 

 Transition Zones. 



The chaetognaths and pteropods of the central 

 North Pacific could be segregated according 

 to species composition into three faunal 

 zones: 



a. The Subtropic Zone, as defined by the 

 abundance of the chaetognath Pter osagitta 

 draco, was a region of great species 

 diver sity with relatively low biomass and 

 characterized by relatively high tem- 

 peratures and salinities. The boundaries 

 of this zone were essentially the same 

 in winter as in summer but fluctuated 

 widely in the fall. 



