590 WHAT IS OVER-FISHING ? 



essential point in the matter. I do not think it necessary further to 

 discuss it here. 



When the " P " grows fast, we might take predatory animals into 

 consideration as a cause of the reduction in the average size of the 

 " P." It will then have to be investigated which predatory animals 

 attack the big " P " more severely than smaller ones, I think it is not 

 very probable that such animals exist. At all events, I do not know of 

 such animals, and have never heard of any. 



Other organic factors (diseases) may, perhaps, be mentioned as capable 

 of reducing the average size of the " P." We do not, however, know 

 anything about this; but from our investigations (1) we know the quick 

 rate of growth of the marked " P," and (2) we see that their mortality, 

 except by fishing, is not great in the North Sea. And this is sufficient. 



The first immediate influence of fishing is beyond doubt the reduction 

 in number of the " P." * The second influence of fishing is that it 

 prevents the " P " from being as old, and therefore as big, as in places 

 where no fishing is going on. It is in this latter fact, I think, that we 

 have to look for the reduction of the average size of the " P " in the 

 North Sea and in the Kattegat. When admitted that we have not to 

 do with an accumulated stock of " P " in the North Sea, but only with 

 a stock of the II, and a small part of the III Group of " P " highly 

 reduced by fishing and growing up again every year nearly, but not 

 quite, to the same point as the year before, it will be understood that 

 the average size has been slowly reduced year by year. Somebody 

 might already regard this reduction of the average size as over-fishing, 

 yet it is not absolutely so. We suppose that the mature fish. Group III, 

 have been greatly reduced in numbers, but are still capable of yielding 

 sufficient eggs to keep the stock up to date. According to the custom 

 of nature, it is probable that in former times eggs and young fishes 

 were produced in overcrowding multitudes, and that a very high per- 

 centage consequently died out. The mature " P " may undoubtedly 

 become so scarce that they cannot supply the stock sufficiently with 

 eggs. If this be so, we have to do with one kind of over-fishing of the 

 mature " P " which reduces the number of " P." I do not, however, 

 suppose this to be the case, but rather that there is a sufficient supply 



* It is possible to imagine that reduction of the III Group by fisliing may after- 

 wards allow the II Group to spread over a larger area, and consequently procure more 

 favourable conditions for the individuals of this group : (1) they will grow quicker, and 

 (2) the mortality will perhaps be reduced, and the total number of all "P" will thereby 

 in a twelvemonth be larger than before the fishing was carried out. This would be a 

 peculiar result of over-fishing. Whether it really is over-fishing depends upon two things : 

 (1) the amount of reduction of the average size, and the price of the fish at this reduced 

 size ; (2) the extent of the increase of the numbers and rate of growth of the II Group. 

 Statistics must solve this problem. 



