314 



DISCOVERY REPORTS 



in nearly all groupings. The seasonal variation in ponderal index shows a rise in all three regions from 

 spring and summer to autumn. These results are also shown graphically in Fig. 28. 



Table 29. Data selected over short-time intervals in each region, to show the increase in ponderal index of 

 Macruronus magellanicus during the season, with corresponding figures showing relative abundance, 

 mean lengths and sex ratios, and the mean sex ratio for each region 



i 



Mean date 



Total 

 Macruronus 



Hours 



positive 



hauls 



Fish per 

 hour's 

 + haul 



Sex 



ratio 



i, males 



Mean 



length 



cm. 



Average 

 K 



Sex ratio 



mean for 



region 



23. X. 31 

 15. xii. 31 

 23. iii. 32 



37 

 1089 



45 



2. XI. 31 

 20. xii. 31 

 23. iii. 32 



570 



153 



48 



3 



15 



I 



Intermediate region 

 39-9 



190 

 10 

 48 



49-0 

 43-8 



38-9 

 37-6 

 40-6 



0-270 

 0-345 

 0-358 



41-9% 



<S3 



16. i. 32 

 8. ii. 32 

 2. iv. 32 



1321 



36 

 1212 



24 

 2 



5 



Southern region 



45-8 

 44-4 



55 

 18 



242 



38-0 



47-1 



55-9 

 49-0 



0-311 



0-322 

 0-343 



42-1% 



36 



The figures for 'average' K are means of means. The fish were weighed in length groups, their 

 individual lengths being known, but of course the numbers included in the weighings differed widely. 

 Little difference between ponderal index of males and of females could be detected. The averaging of 

 the ii: values obtained within the time limits stated is an attempt to obtain a general indication of the 

 direction or trend of the seasonal variation, although the figures have no precise significance. The 

 fact that they indicate a rise in ponderal index in each of the three latitudinal regions over the period 

 studied seems, however, strongly significant in the general sense, though not demonstrable mathe- 

 matically. The implication is that Macruronus spawns in spring. 



0-350- 



2 



^ 0-300 ■ 



5 



OCTOBER NOVEMBErIdECEMBERI JANUARY IfEBRUARY I MARCH I APRIL 



Fig. 28. Seasonal variation in mean ponderal index of Macruronus magellanicus: • northern 

 region, ■ southern region, A intermediate region. 



We have seen that in summer the fish is most numerous in the southern region, from which it was 

 absent m winter. Thus the direction of movement in spring and summer must include a considerable 



