F-17 



Table 6.4' (From Mackintosh 1972) Mean dates for major spawning and hatching of Ej_ superba 



V/orking on samples collected in the vicinity of the South Orkney Islands (equivalent to 

 Mackintosh's Scotia Sea area) Makarov (1973) describes spawning as occurring at the end of 

 February and that the timing of the peak is very much dependent on temperature. In warm 

 years he suggests the sea ice clears earlier thus allowing an earlier start to the growing 

 season with a resultant earlier spawning. 



The main purpose of Mackintosh's analysis of spawning date was aimed at providing an 

 origin for the gi'owth curves for results from different areas. He was therefore only con- 

 cerned with the mean date of spawning and took little account of the several month variation 

 in the observed dates on which eggs were found. Marr (1962) in considering the overall 

 spawning season in the northern or Weddell zone did not consider spawning as a short-term 

 outburst, as had been suggested by Ruud (1932), but suggested it occurred over the period 

 November to March. The recent work of Makarov (1975 » 1976) has indicated that individuals 

 spawning for the first time do so late in the season (February, March) whilst those which 

 live for a further year spawn for a second time during the November, December, January period. 

 The release of eggs during most months of the production season will almost certainly result 

 in a broad size frequency distribution for each year class (if year classes can be identi- 

 fied). This in turn could also result in the production of an intermediate size group (see 

 section on growth) as has already been discussed. Clearly it is only when definitive spawn- 

 ing periods in given locations are identified and the development of the subsequent size 

 groups are followed that it will be possible to subdivide the broad size frequency distri- 

 butions and thus help in unravelling the growth story. 



The infonnation reviewed by Hauchline and Fisher (1969) indicates that euphausiids gen- 

 erally spawn in the spring or early summer and that by spawning at the end of the summer 

 E. superba is an exception. It is however possible that originally the spring breeding 

 season now identified by Makarov may have been the norm and that the late summer spawning 

 has only recently evolved. No matter what the sequence of evolution it is probable that the 

 two spawning periods represent a fail safe device in maintaining a hif^ biomass. 



Fecundity 



Estimates of fecundity are few and include a wide range of values as a result of diffei^ 

 ent techniques in estimation. These are reviewed by Mauchline and Fisher (I969) who consider 



1/ (N.B. There is very little evidence of successful spawning in the vicinity of South 

 Georgia). 



