2 72 DISCOVERY REPORTS 



Fig. 26 shows the data from the shallow oblique (1 m.) nets fished in the Subantarctic zone during 

 the months of May to November. The animals have been plotted in 5 mm. size groups, the numbers 

 of each group calculated as a percentage of the total haul or set of hauls. Each haul or set of hauls has 

 been plotted against the day or mean of the days on which they were made. Regrettably it has not been 

 possible to utilize data from one area alone (or from one year alone) as the numbers available in the series 

 of repeated stations on o° have been insufficient by themselves. Thus Fig. 26 is composed of data from 

 many localities taken in several different years. The results are, however, remarkably consistent, and 

 this suggests that the general pattern of breeding and development is the same from year to year 

 throughout the Subantarctic zone. 



The variation in the upper size limit during the winter months may well be due to the variation in 

 depth of the nets; for example the first set of June observations made at Stations 2824 and 2825 show 

 a greater number in the larger size groups than the other June observations, because the net at 

 Station 2824 was fished from 163 to o m., and thus sampled the older and larger-sized broods below 

 100 m. The smallest size groups are affected by the occasional presence of a small brood hatched later 

 than the main one under consideration ; this later brood seems to separate out in September. 



881/92 

 I 



2648/') 2538 



1 r 



2459/60 983/90 2736/36 1614 



^r 1 r 



Fig. 26. The growth of S. gazellae, based upon counts and measurements of specimens taken in the shallow oblique 1 m. nets. 

 The station numbers of the hauls used are given along the top and the number of individuals in each haul or set of hauls is 

 enclosed in each figure. 



The growth rate from May to October is shown by Fig. 26 to be about 5 mm. per month. This is 

 evidently a low rate which is most probably higher in spring and summer, and which appears to be 

 lowest during August. The normal size at maturity is 55-60 mm. and this would be reached in 

 12 months at a 5 mm. per month growth rate : Figs. 8 and 15 suggest that the maximum size is reached 

 in the surface layers, for none of the mature animals (found in the deep layers) was larger than at 

 stage II which is the most advanced stage found in the surface layers. Thus in considering the growth 

 rate one must make allowance for both the time needed for the breeding migration, and the time taken 

 for the maturation of the gonads. It has not been possible to discover how much time elapses between 

 the commencement of the breeding migration and the shedding of eggs. If one assumes that for at 

 least 1 month, and possibly 2, no growth takes place, then the summer growth rate must be somewhat 

 higher to achieve a length of 60 mm. in 10 or 11 months. This seems a reasonable assumption, as the 

 food supply is much greater in spring and summer. 



There are certain stages in the life history of S. gazellae which I have been unable to find, but in 

 most cases they can be inferred from other evidence, and it may be possible at some future date to fill 

 in the gaps, now that it is known when and where to look for those stages. 



