330 DISCOVERY REPORTS 



There is no doubt that spawning takes place in any given locahty at different 

 times in different seasons. In 193 1-2 it took place east of South Georgia in the 

 first fortnight in December. In 1929-30, however, Ottestad found a young generation 

 in stages ii, iii and iv already developed at the end of November and the beginning of 

 December. The Vikingen stations were taken considerably farther east at this time than 

 the most easterly of the Discovery II stations in early January 1932. In the season 1929-30, 

 therefore, spawning must have taken place east of South Georgia somewhere about the 

 beginning of November, It is probable that the time of spawning depends on some 

 variable factor, and one may suggest, as the most likely one, the break-up of the pack- 

 ice and the southward movement of the isotherms in this area. The season 1929-30 was 

 an exceptionally mild one ; the pack-ice was far south and there was no sign of it around 

 the South Sandwich Islands. In the season 193 1-2 the pack-ice was north of the South 

 Orkneys at the end of the first week in December and around the South Sandwich 

 Islands probably in early January. It may be that the difference in the time of break-up 

 of the pack in the two seasons accounts for the difference in the spawning time of 

 Rhincalanus. 



Weddell Sea, fnid-December 193 1 to mid-January 1932 

 (Fig. 22, Table VI c) 



We have now to examine the Rhincalanus populations at the remaining stations in the 

 South Atlantic area. They all lie in the Weddell Sea current, and it will perhaps be best 

 to consider them in relation to the Weddell Sea as a whole. 



At stations in the "oldest" Weddell Sea water (average temperature for o-ioo m. 

 between o and i-o° C.) — Sts. 779, 795, 798, 806 and 808 — the catches (except at St. 

 779) consist of stage v, with varying proportions of stage vi. No young forms were 

 found at any of the stations in the Weddell Sea, except at St. 804, where a fair propor- 

 tion of stage iv were taken in the upper net together with a very few stage iii. From this 

 fact one may conclude that before the end of January, at any rate, no spawning took 

 place in the Weddell Sea. At each of the stations in the "oldest" Weddell Sea water 

 (o-i-o° C.) the larger proportion of the catch was in the lower nets and hence it may 

 be supposed, as already mentioned, that the population originated mainly from the 

 warm deep water of the South Atlantic or Scotia Sea, which here mixes with colder 

 Weddell Sea water at the surface above about 200-250 m. At these stations (Fig. 22) the 

 stock consisted predominantly of stage v. At the most westerly station (779) in the 

 "oldest" Weddell Sea water the stock consisted predominantly of adults. At Sts. 763, 

 765 and 768, taken in the Scotia Sea in water of Weddell Sea origin (Table VI b, 

 Fig. 20), it must be assumed that the population in both nets is of mixed origin, since 

 a high degree of mixing takes place in this particular area. However, the main body of 

 the catch at these stations occurred in the upper nets, so that most of the population 

 sampled by them is perhaps derived from Antarctic surface water which has spent 

 some time in the Scotia Sea, since the water derived most recently from the Weddell 

 Sea will probably be concentrated in the lower stratum of the surface layer. Adults 



