EUPHAUSIACEA 2IQ 



Thysanoessa vicina, Hansen, and T. macrura, G. O. Sars. The two species were widely 

 distributed in the area, but T. vicina was on the whole taken in larger numbers than was 

 T. macrura. Specific identification of the males only of the two species was carried out 

 in the analysis of the N 70 V net samples taken throughout the survey, but in the 

 N100H samples this identification was only carried out for the first season, March and 

 April, 1926. Identification was often rendered difficult by the mutilation of specimens 

 by the attacks of carnivorous Amphipods taken in large numbers, particularly Parathe- 

 misto, before the samples were preserved. Thus whilst the N 100 H nets give the better 

 information as to the numbers of Thysanoessa present at different stations throughout 

 the survey, the N 70 V nets give us some information regarding the relative abundance 

 of the two species. The results of the N 100 H nets are shown in Fig. 95 and of the 

 N 70 V nets in Fig. 96. 



The relative numbers of the two species taken in the N 100 H nets in March and 

 April 1926, will be found in Appendix II, where it will be seen that T. vicina is the 

 predominating form. Since all these stations are in a very small area the considerable 

 variation in numbers would suggest that the two species are, like Enphausia superba, very 

 patchy in their distribution. 



Thysanoessa macrura has been taken from the sub-Antarctic and Antarctic regions by 

 most expeditions: Challenger, 1 Belgica, 2 National Antarctic (Discovery), 3 Swedish 

 Antarctic, 4 Gauss, 5 Scotia, 6 Francaise, 7 Terra Nova, 8 Aurora, 9 Norvegia 10 and Vikingen 11 

 Expeditions. All these records are from south of the isotherm of 12 C, except one 

 of the Challenger records from 37 17' S and 53 52' W. It appears to have a range 

 similar to that of Enphausia superba. 



Thysanoessa vicina has not been taken so frequently, or in such large numbers, as 

 T. macrura by the past expeditions, i.e. only by the National Antarctic (Discovery), 3 the 

 Swedish Antarctic, 4 Gauss, 5 and Terra Nova 8 Expeditions. As pointed out by 

 Tattersall (1924), all the records are between the limit of pack-ice and the isotherm I2°C. 

 Rustad (1930) sums up its distribution by saying, "Altogether the few finds of T. vicina 

 indicate a more northern habitat in comparison with T. macrura". The results of our 

 survey taken in conjunction with the results obtained by Rustad and Ruud confirm this. 



South Georgia is evidently a region where T. vicina flourishes, but T. macrura is 

 reaching its northern limit, and a little to the south of South Georgia T. vicina probably 

 meets its southern limit. Very few T. macrura appear on the oceanic line towards the 

 Falkland Islands. At St. 161 far to the south-west of South Georgia no T. vicina were 

 recorded and only one T. macrura. Turning to the results obtained by Rustad (19306) 

 in the 'Norvegia' and Ruud (1932) in the 'Vikingen' each working to the south or 

 south-east of South Georgia, we find that they met with no T. vicina at all, but only 

 T. macrura. 



There is some indication that the species may undergo a vertical diurnal migration, 



Sars (1885). 2 Hansen (1908). 3 Tattersall (1908). 4 Hansen (1913). 



Zimmer (1914). 6 Tattersall (1913). 7 Coutiere (1906). 8 Tattersall (1924). 



Tattersall (1918). 1(l Rustad (19306). n Ruud (1932). 



