Table 4. --Seasonal variation in the distribution of Pterosagitta draco with associated 

 surface temperatures and salinities 



* = limits of sampling 



since it was the only species that was 

 consistently abundant. It is possible that the 

 use of other species of chaetognaths and ptero- 

 pods might have changed the boundaries to some 

 degree. Although our data are incomplete with 

 respect both to area and to season, the position 

 of the northern boundary of the Subtropic Zone 

 appears to shift latitudinally with the season and 

 to vary somewhat with longitude. During both 

 the winter and the summer periods (fig. 2) the 

 boundary was confined between 31°N. and 

 34''30'N. latitude for the longitudes sampled. 

 It showed the widest latitudinal variation in the 

 fall, when it ranged from 3 1 ° 12 'N, to 39°28'N. 

 between longitudes 145 °W, and WO'E, Sinnilar 

 results were obtained by Beklemishev and 

 Semina (1956). 



The summer temperatures at the northern 

 limits of the zone ranged fronn 75.5*F, to 

 78,7'F. with salinities from 34,82%o to 35.32%o.l/ 



— All temperature and salinity data given 

 in this paper are surface values, except for 

 those of figure 4. 



The winter tennperatures ranged from 60, 8*F. 

 to 67'F. and salinities from 34. 58%o to 35, 12%o, 

 On the average the temperature difference be- 

 tween summer and winter conditions at the 

 northern limits of this zone was about 13*F., 

 with salinities remaining fairly stable. In the 

 fall temperatures varied from 58*F. to 77*F, 

 and salinities were as low as 34.07'/oo. This 

 environmental instability during the fall months 

 was perhaps due to the extrennely changeable 

 and generally adverse weather conditions pre- 

 vailing in the area at that time of year. The 

 temperature and salinity data at the northern 

 limits of this zone are included in table 4, 



Transition Zone 



An area of mixed fauna and variable biomass 

 (fig. 1) between the Subtropic and Subarctic 

 Zones was arbitrarily designated the Transition 

 Zone (tables 1 and 2). The fauna near its south- 

 ern boundary resembled that of the Subtropic 

 Zone with a decrease in abundance of the four 

 abundant Subtropic Zone chaetognaths, particu- 

 larly P. draco but also S. hexaptera , S, 

 serratodentata, and S. bipunctata, and an 



