— 104 -— 



fish, it is difficult to utilize the statistical data on this class for a more detailed study of 

 the occurrence of the immature and also of the mature fish. The results must remain 

 obscure if there should be a noteworthy difference in regard to their migrations between 

 the mature and immature fish. 



On the other hand, the data on the "large" and "extra large" can give us better 

 information, as all the individuals within these groups are mature. We find in D'Arcy 

 Thompson's report some interesting charts showing the maximum distribution of the two 

 groups "extra large" and "large" during the different seasons, and it appears from these 

 that both groups show a tendency to occur in greatest quf^ntity in winter and spring in 

 two large regions, namely, (i) north-west of Scotland and (2) in the extensive deep part 

 of the North Sea. These are preeminently the fishing grounds of the largest groups. It 

 is very interesting that these facts agree with the earlier described observations on the 

 occurrence of the plankton eggs. Thus, both the statistics and the occurrence of the 

 eggs show that the waters west and north of Scotland and the deep, northern part of 

 the North Sea contain the richest spawning places of the haddock. 



Away from the spawning time the richest catches are made in other areas in summer 

 and autumn. There is a summer maximum of the "large" class at Shetland, in the 

 Skager Rak and in the Southern North Sea. South of the Shetland Isles and along the 

 east coast of Scotland the greatest catches of the "large" class occur in late summer and 

 autumn. The "extra large" class occurs in the deep Northern North Sea in great quan- 

 tities chiefly in the months of February and March ;, for the rest the catches of this group 

 show a summer maximum at the Orkney Isles and in the Skager Rak. 



From the figures given by D'Arcy Thompson we obtain a clear impression of how 

 marked these changes are. We reproduce here two of his curves, both of which show 

 the monthly catch of the class "large" during the years 1901 — 1906. The one figure 

 (fig. 37) shows the catch on two areas off the east coast of Scotland. It is very interesting 

 to note, how the curves for both areas follow each other exactly. Both show maxima 

 from August to October and but small quantities in the period from February to April. 



Fig. 38 shows the conditions south of the so-called Witch Ground in the central part 

 of the North Sea. This figure is characteristic for the whole large area and is remark- 

 able for the distinct maximum in the period from December to February. The great 

 changes which these curves show in the occurrence of the large haddock in different 

 areas of the North Sea, can with difficulty be explained in any other way than that these 

 larger, older fish undertake extensive migrations. It has certainly not been possible 

 as yet to investigate these migrations by marking experiments and the purely experimental 

 proof for the correctness of this view is thus lacking. It must also be admitted, that the 

 results which the investigations with the trawl have on the whole yielded, are not quite 

 complete, since the trawl takes almost exclusively the fish which live on the bottom, and 

 the possibility is at least theoretically not excluded, that the variations in the catches are 

 to be referred to vertical migrations up and down in the water and not to migrations 

 from one area to another. But even if we allow so much weight to this possibility, it 



