334 



DISCOVERY REPORTS 



30- 



;20- 



10 



B 



Fig. 38. Percentage length 

 frequencies of A'^. ramsayi 

 taken (A) between 51 and 

 100 m., and (B) between loi 

 and 150 m., in spring. 



We have no extensive autumn data for the smallest Notothenia ramsayi, but the pooled length 

 frequencies of spring samples taken in 51-100 and 101-150 m. show such strong modes about 

 8-10 cm. (with the larger fish in the deeper water) that it is reasonable to assume that they represent 

 a year class. These fish are thought to have been almost one year old — o-group becoming I-group 



(Fig. 38). 



In autumn we obtained eleven rich hauls of between eighty and 161 6 individuals of this species, 



and on plotting the percentage length frequencies (Fig. 39) it appeared that modes at around 14-16 and 



22-23 cm. recurred with such consistency that there can be little doubt 



that they represented year classes. They are thought to indicate I-group and 



I I-group fish respectively. The scale of the figure is necessarily much reduced, 



in order to permit comparison of all the samples on one page. Table 33, 



summarizing the important points arising from Fig. 39, and giving relevant 



geographical data, has been prepared to cover any loss of information due 



to the unavoidably small scale of the figure. 



It will be seen that clear evidence of either or both of the two year classes 



mentioned is provided by all but three of these samples notwithstanding 



their diverse locations. At St. WS83 there was a strong mode at 17 cm. — 



considerably higher than the modal values for most of the presumed I-group 



fish captured around that time, which were at 14 and 15 cm. It is believed 



that this is explained by the geographical position of St. WS83 — close in to, 



but on the southern side of, the Falkland Islands, considerably farther south 



than any other station at which such small A^. ramsayi have been taken in 



quantity. From the general distribution of the species as already described 



it seems at least highly probable that only the largest members of the I-group 



would be likely to penetrate so far south. This notion is perhaps strengthened by the strong 14 cm. 



mode shown by the sample from St. WS73, almost equally close in to the islands, but to the north 



of them. 



The very rich sample from St. WS97 yielded length frequencies which are not incompatible with 



the idea that the Il-group predominated, but the mode is ill-defined, as stated in Table 33. The 



suggestion that this may be due to the slower growth rate of mature males as compared with females 



is strongly supported by the fact that such sexually differentiated grovi^h is known to take place in 



various other fishes (e.g. hake). 



Finally, at the only deep station at which a large haul of N. ramsayi was secured in autumn, 



St. WS214, it seemed that we were dealing with an altogether larger age group (? Ill-group) with the 



mode at 27 cm. This would be in full accordance with our findings as to the general relation between 



depth and size of fish where N. ramsayi (and many other species) are concerned. 



Considering these results in conjunction with the general distributional data, it seems probable 



that early growth of N. ramsayi takes place somewhat as follows. The fish probably hatch in early 



summer and grow rather more than 10 cm. in their first year of life, at least 8 cm. in their second year 



and 6 cm. in their third. At this point maturity is probably reached and no reliable conclusions can 



be drawn from unsexed data, for it is probable that mature females grow considerably faster than 



males, but there is some evidence suggestive of a 4-5 cm. increment during the fourth year. 



I have included this brief and admittedly speculative suggestion as to growth rate in N. ramsayi 



because it will at worst provide a working hypothesis if any future work on the shelf is possible, and 



we know so little of the growth of any of the fishes in southern temperate waters. 



Several records of the stomach contents of A^. ramsayi were made in autumn and winter, when some 



75 % of the fish contained recognizable food. The number of times food of each category was recorded, 



