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SOME EESULTS OF THE INTERNATIONAL FISHERY INVESTIGATIONS. 477 



of these statistics is the "complementary fluctuations" among different 

 flat-fishes inhabiting the same ground. In the case of one particular fish 

 the abundance varies, of course, with the season ; but the periods of the 

 year at which a fish is most abundant differ for many of the species 

 considered. In one area considered, for instance, megrim were most 

 abundant about May, plaice in April and September, witches in June 

 and July, halibut in April, and lemon-dabs in September. Thus the 

 scarcity of one species was compensated for by the abundance of 

 one or more others, so that on any one fishing ground the general abun- 

 dance of all the flat-fishes was maintained throughout the year at 

 roughly the same level. In the case of nearly every one of the fishes 

 studied the fluctuations from month to month exhibited undoubted 

 regularities. It was nearly always possible to deduce that on each 

 fishing ground there was one month during which each species of fish 

 was present in greatest abundance. This maximum in each case corre- 

 sponds with the spawning season and indicates an aggregation of the 

 fishes on particular areas for the purposes of reproduction. Following 

 this spawning maximum of abundance, the period of which, of course, 

 varies with each kind of fish, is a period of relative scarcity. Then 

 occurs a secondary maximum some time in the autumn, when the fish 

 is again abundant, though usually not so abundant as in the spring or 

 summer spawning maximum. Then in the winter there is often 

 another period of relative scarcity. These remarks apply to the study 

 of the fishes present on each particular fishing area throughout 

 the year. How the abundance of each kind of fish is dis- 

 tributed throughout all the separate fishing areas may be seen by 

 considering the charts of the fishing grounds published by D'Arcy 

 Thompson in the paper referred to above. These show for each month 

 in the year the average amounts of cod, ling, saithe, hake, haddock, and 

 whiting caught on each area per 100 hours trawling by the Aberdeen 

 trawling fleet. Their charts simplify greatly the study of the statistical 

 data. The variations in fish abundance displayed by them are interest- 

 ing and well worth study by the reader. 



The aim of the master of a fishing vessel is, of course, to get as much 

 fish as possible. Therefore he does not always frequent the same 

 grounds, but fishes from place to place over the North Sea, following 

 the fish shoals, getting varying catches on the various grounds. At one 

 time one kind of fish may predominate, during another month other 

 kinds. Long experience, and many fruitful or fruitless experiments, 

 have taught liini where and when to expect good catches. If this 

 practical knowledge of the fishermen could be systematized, sifted from 

 error, and recorded, we should possess a knowledge of the seasonal 

 fluctuations and migrations of the fishes which, supplemented by the 



