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between the different portions of the North Sea but also between the different 

 5'ears. These total numbers were more minutely analysed in relation to size and 

 age of individuals, whereupon it was shown e. g. that the results thus obtained 

 coincided with the English fishery statistics which are concerned with such 

 enormous weights of haddock. It is probable that in the case of this species the 

 material of the Research Steamers has been fairly representative, when it was a 

 question of showing the general composition of the aggregate in regard to size 

 and age and of indicating the variations from one year to another. But even in 

 this respect it has not been as representative as one could wish, seeing that the 

 researches have not been more evenly distributed with regard to both place and 

 time. Future investigations will have to aim at getting all the different areas 

 examined with equal exactitude, and at carrying out the researches annually 

 during several fixed periods, in such a way as to obtain from each of them a 

 really adequate material. 



The great variations in the haddock aggregate are due to mighty phenomena 

 that are qiiite irrespective of the intervention of man. We may assuredly consider 

 it as proved beyond a doubt that in the North Sea there have been comparatively 

 very few haddock that have been spawned in 1903, but very large numbers of 

 individuals, which have been spawned in 1904. Moreover differences like these are 

 very noticeable in the whole haddock aggregate in the North Sea, and the 

 conditions in any one given year materially affect the yield of the fisheries during 

 several subsequent seasons. 



Statistical researches such as ours cannot explain the reasons why the 

 accessions of new individuals differ so remarkably, and other investigations must 

 deal with the question as to whether these fluctuations are due to differences in 

 intensity of spawning or to great variations in the mortality of eggs and larva; 

 or whether they are the result of currents carrying the pelagic stages into or 

 away from these waters in more or less varying degree. It is, too, jtrst as im- 

 possible for us to decide by means of our material whether these fluctuations 

 have merely affected the North Sea, or whether similar variations have occurred 

 in the entire haddock aggregate throughout all the North-European waters of 

 which the North Sea merely constitutes a minor part. 



Still leaving out of account the causes we may fairly claim that our results 

 are undeniably wide-reaching, both because they point to the possibility of making 

 fishery forecasts and because they show that as compared with mighty natural 

 phenomena, intensive fishing has only a minor effect upon the haddock aggregate 

 in the North Sea. There were comparatively slight variations in the numbers of 

 the highest groups (Large and Extra Large) during the years to which our 

 investigations refer; thoitgh it is quite conceivable that the variations in the 

 numbers of the various year-classes have become imperceptible there in view of 

 the fact that these groups consist of many year-classes. Moreover (cf. Heincke's 

 investigations) the large haddock are essentially migrants which mainly freqiient 

 more northerly and deeper waters than those we have been investigating. Their 

 numbers will therefore depend upon immigration from areas where conditions 

 may have been totally different. But in the case of the lower groups the variations 



