3i6 DISCOVERY REPORTS 



southerly component. Further, it is highly probable that Macruromis spawns in spring, for the 

 ponderal index rises during the summer. Many fishes feed most heavily just after spawning and it 

 would seem that the movements of Macruromis during summer are essentially a feeding migration. 

 The search for food may be expected to lead to considerable dispersion, and to local concentration 

 where food is plentiful. This would help to explain the greater variation in size of Macruromis catches 

 when compared with the catches of hake, whose summer movements are more in the nature of a 

 breeding migration. At two of the large southern hauls of Macruromis the fish were observed to be 

 glutted with clupeoids — probably the most important food of the larger individuals — and I think it 

 probable that the southern concentrations oi Macruronus and Clupea fuegensis will be found to coincide 

 in summer. 



Small immature individuals of Macruromis were found mainly to the north of our area, in com- 

 paratively shallow water. The southward movement in summer seems mainly confined to the larger 

 mature individuals. Although a clear gradient in relative abundance and increasing size of individuals 

 cannot be shown in lumped data as we proceed southwards from the northern region through the 

 intermediate region, the greater abundance and size of individuals of the southern region population 

 is clear however the data are arrayed. Over a short-time interval in March, the length frequencies 

 clearly show the increase of size with increase of latitude (Fig. 29), and there is little doubt that this 

 would have been apparent at other times had it been practicable to work more north and south lines. 



The distribution of Macruronus in relation to depth has been found to have an important bearing 

 upon the problems of its movements. The depth relations from all data, regardless of region, are 

 shown in Table 30, where the catches have been grouped in 50 m. depth classes. From this it is at 

 once apparent that it is very much an inhabitant of the plain of the shelf, showing a marked falling off 

 in relative abundance at depths greater than 150 m. It was never taken below 300 m. and, as can be 

 seen by comparing the individual depths given in the Appendices with the catch records already listed, 

 nearly all the deeper records were obtained in autumn. This may imply some offshore movement 

 superimposed upon the meridional movement of which evidence has already been given. 



Table 30. Data summarizing the depth relations of Macruronus magellanicus 



The depth distribution is particularly interesting in relation to the mean lengths. In each of the 

 three deeper depth categories in which Macruronus was found these slightly exceeded 53 cm., and no 

 significance attaches to the slight differences between them. But in slightly shallower water, where 

 the vast majority of our specimens were secured, the fish were much smaller, of mean length 42-8 cm., 

 the difference from the means for all three deeper groupings being strongly significant. In the next 

 shallower depth category there was a marked falling off in relative abundance and the fish were even 

 smaller. Their mean length was 40-1 cm., and the further small decrease of 2-7 cm. in mean length is 

 statistically significant. These data show that larger, mainly mature, fish preponderate in the smaller 

 catches of Macruronus from the greater depths in which the species was found, while smaller mainly 

 immature fish predominate in shallower waters. We have already seen that the smaller fish tend to be 



