F-16 



Table 6.3. Summary of infonnation related to life epsm in EuphauBJa euperba 



Recent work (reviewed in the section on Reproduction )has shown that a significant pro- 

 portion of the population spawn for a second time althou^ the growth increment in this 

 additional year is only small. 



The information that is available althou^ far from conclusive indicates that the growth 

 pattern originally described by Ruud (1932) and Bargnann (1945) is probably correct. There 

 is however considerable doubt about this and the possibility that the intermediate size group 

 does represent an additional year class has neither been conclusively proved nor disproved. 



6.4 Reproduction 



A good general description of the reproductive biology of euphausiids is given by 

 Mauchline and Fisher (1969), whilst detailed specific information covering the main aspects 

 of reproductive biology is available in Bargnann (1937) and Praser (1936). The topics of 

 particular interest in this review are spawning season, fecundity and the phenomenon of 

 repeated spawning. 



Spawning season 



It is now generally accepted that spawning by Ej. superba occurs at the surface (see Marr 

 1972, Pig. 30, Voronina 1974, Makarov 1974) during the summer months. In a brief review of 

 published information on the precise spawning period Mackintosh (1972) suggests that it is at 

 its peak in February and March althou^ gravid and freshly spent females were found from 

 November to April. In general he describes the 3i)awning season as being earlier in the 

 northern end of the range than nearer the continent and gives the following "best estimates" 

 of mean hatching and spawning dates (Table 6.4). 



The dates (Table 6.4) were calculated to provide the origins of growth curves from the 

 different regions and are estimates based on the known spavming dates in the Weddell aind 

 i^st V/ind Drift zones. Thus, although they are presented within fairly broad limits and 

 are subject to local annual variation, they are useful at this stage as a first approximation. 



