G-27 



The eeaeonal cycle in the ovary of all fish species eo far studied, whereby there is a 

 steady build up of oggs all of the same size, indicates that H].)awning Beaeons of limited 

 duration are normal. The result of this is that it is to be expected that just prior to 

 and during spawning the mature fiah will be congregated together. That this occurs is 

 undoubtedly the case as concentrations of mature fish have frequently been caught on th« 

 continental shelf of some of the island groups. The approximate localities and environmental 

 characteristics of these localities are summarised in Table. 8t23» It should be borne in mind 

 that the list. only includes localities where presjawning or spawning fish have been caught 

 and obviously does not include all spawning areas. It is probably fair to assume that spaw- 

 ning concentrations will occur in similar circumstances to those described in the table over 

 most of the range of each individual species. 



Table 8.23. Sjiawning localities and environmental characteristics of spav-ming groiinds. 



(S.G.: South Georgia; S.O,: .".oul.h Orkneys; S.S.: South Shetlands) 



Mention has already been made of the slow growtli rate of Antarctic fish. A direct re- 

 sult of this is that sexual maturity is not reached until the fish are several years old. 

 Information on size and age at sexual maturity is set out . in Table 8. 24* Precise information 

 is not aval] able for most species and several are estimated from the information in the lit- 

 erature. 



Spawning migrations have been described in few species although there are indications 

 generally based on negative evidence that several other species perform spawning migrations. 

 Keysner et al. (1974) described a migration of N. rossii in May from the feeding ground 

 north of Kerguelen to the spawning grounds to the south of the Island. The spawning grounds 

 are characterised by high oxygen content and a rocky EOibstrate. The migration itself is thought 

 to be in the same direction as the prevailing current which in the area has a strength of 0.6 

 to 1.0 kt. The post spawning northward movement in August back to the feeding grounds is thought 

 to be made in a northerly flowing current offshore of the southward flowing current of the 

 spawning migration. 



