276 DISCOVERY REPORTS 



uncommon in the Southern Ocean, and so it is not likely that they represent major predators of 

 S. gazellae. Dr T. J. Hart has observed a Cape pigeon (Daption capensis) holding a large sagittain its 

 beak, and from the position of the observation it is fairly certain that the sagitta was S. gazellae. 



S. gazellae is probably eaten by most of the larger plankton-feeding organisms in the Southern 

 Ocean, but no records are yet available. 



Table 17. Food organisms found in the gut of Sagitta gazellae arranged by groups in order of 



frequency of occurrence 



SUMMARY 



i . Sagitta gazellae has been examined from a series of stations made by ships of the Discovery 

 Committee in the Southern Ocean. 



2. The species is shown to be separate from S. lyra (Krohn) with which it has been considered 

 synonymous in recent years. 



3. Five stages of maturity based upon those of Kramp (1939) for S. maxima are outlined. 



4. The population of S. gazellae in the Southern Ocean consists of two races divided by the Antarctic 

 Convergence. The Northern or Subantarctic population matures at a shorter length than does the 

 Southern Antarctic one. 



5. The limits of horizontal distribution are shown to be, to the north, the region of the subtropical 

 Convergence, and to the south, the Antarctic Continent. The region of maximum abundance of the 

 species is in the Subantarctic zone. 



6. The species has an observed vertical range of 3000-0 m., with a layer of maximum abundance 

 between 100 and 50 m. 



7. S. gazellae performs a seasonal vertical migration to deep water in winter, but does not perform 

 any diurnal migration. 



8. The Subantarctic race is shown to have a growth rate of 5 mm. per month during the winter 

 and early spring. The growth rate is presumed to be higher in summer. 



9. The species breeds only in deep water (>750 m.). The breeding season is very extended. The 

 smallest individuals observed were taken in the upper 250 m. 



10. S. gazellae feeds mainly upon copepods and small euphausians. 



