180° 



I57°30'W 



50° 



45° 



UJ 



Q 



I- 40°- 



I 35° 



I- 



o 



30° 



25° 



PRESENT 



COMMON 



••• ABUNDANT 



i CONSPICUOUSLY ABUNDANT 



Figure 5. --Comparison of the distribution of chaetognaths along the 180° and 

 157°30'W. meridians as found on Hugh M. Smith cruise 30. 



The Transition Zone which lay between 

 the Subtropic and the Subarctic Zones 

 was a zone of mixed chaetognath and 

 pteropod fauna with highly variable bio- 

 mass and intermediate values of tem- 

 perature and salinity. The chaetognath 

 Sagitta lyra and the pteropod Limacina 

 inflata occurred here in greatest 

 abundance. The chaetognath Sagitta 

 minima was abundant only in this zone 

 and scarce or lacking in the other zones. 



The Subarctic Zone, as indicated by an 

 abundance of the chaetognaths Sagitta 

 elegans or Eukrohnia hamata and the 

 pteropod Limacina helicina, was an area 

 of high bionnass with very little species 

 diversity, and was characterized by 

 cooler and less saline waters. The 

 southern limits of this zone remained 

 fairly stable in summer and fall, but 

 there were indications that it moved 

 southward in winter. 



plankton collections, showed the presence of 

 three types of water: (a) Subarctic Water of 

 relatively low temperatures and salinities, 

 (b) Pacific Central Water of higher temper- 

 atures and salinities, and (c) a band in be- 

 tween with water of intermediate character. 

 The boundaries of these three types of water 

 corresponded in all essential respects to 

 those of the Subarctic, Subtropic, and Tran- 

 sition faunal zones established on the basis 

 of chaetognath and pteropod distribution. 



Indications are that surface albacore are not 

 confined to a particular type of water as de- 

 fined by the distribution of chaetognaths and 

 pteropods and the temperature-salinity char- 

 acteristics, but are rather associated with 

 certain surface isotherms. In summer the 

 albacore were found in the Subarctic and 

 Transition Zones, in fall they occurred in 

 the Transition and Subtropic Zones, and in 

 winter they were found in the Subtropic 

 Zone. 



Exannination of temperature-salinity 

 relations in the central North Pacific, em- 

 ploying data obtained coincident with the 



11 



