SAGITTA GAZELLAE 269 



100-50 m. nets) it is still necessary to use the temperature and salinity data for the whole 250-100 m. 

 horizon when calculating the mean for the haul, and this inevitably shifts it away from the warm deep 

 layer. 



The change in position of the Subantarctic population in winter is also evident in Figs. 23 a, b, but 

 not enough is known about the characteristics of the surface and subsurface waters in this area to draw 

 any conclusions from these figures, other than to point out a movement down towards the Antarctic 

 intermediate water, which bears out the data from oblique nets. 



JO 



19 

 18 

 17 

 16 

 IS 

 14 

 I 3 

 12 

 I I 

 10 

 9 

 8 



7 

 6 

 5 



4 



2 



(«) 



MARCH 



• 1-5 



• 6-19 

 #20 -i- 



(b) 



JULY- AUGUST 



. • 



33 6 7 89 34 I 234567 



9 35 I 2 3 4 



9 34 1 2 3 4 5 



Fig. 23. The vertical distribution of S.gazellae in relation to temperature and salinity, based on three lines of stations on the 

 meridian of o°, one in summer and two in winter. The core of the South Atlantic Central water is marked S. A. and that of the 

 Antarctic Intermediate water A.I. Above the Antarctic Intermediate water and to the left of the South Atlantic Central water 

 is the Subantarctic surface water. Below the Antarctic Intermediate water, enclosed by two lines is the warm deep water, while 

 to the left of this is the Antarctic surface water. Open circles represent hauls containing no S. gazellae. 



Fig. 25, in which the animals at stage III and IV maturity from N70V hauls have been plotted 

 against temperature and salinity, shows that they are concentrated in the warm deep layer. This is 

 discussed further on pp. 270-1, but the fact must be mentioned here in order to obtain a complete 

 picture of vertical distribution. These mature animals habitually migrate to deep water (750- 

 2000 m.) to breed, and animals sinking down for this purpose are taken at intermediate depths. 



It has been shown above that for most of its life, S. gazellae is an inhabitant of the surface waters, 

 and is mainly concentrated in the 100-50 m. layer; but in the winter months in the Antarctic it sinks 

 to the upper layers of the warm deep water between 250-100 and 500-250 m. At the same season in 

 the Subantarctic, the population is about equally concentrated in the 100-50 and 250-100 m. layers, 

 partly in Subantarctic surface water, and partly in Antarctic intermediate water. 



In winter the smallest individuals form that part of the population which is nearest to the surface, 

 the larger-sized animals occurring below, and increasing in size with increasing depth. In summer the 



5-z 



