19 



APPENDIX F: HENKING 



captains of the boats wishing to avoid the capture of certain species at certain periods of 

 the year; there remains no other possibility, therefore, than that the number of fish in 

 front of the trawl has actually varied. 



This means the admission of a migration; as a simple breaking-up of denser shoals 

 or the collection of scattered fish in shoals can only come in question, when wide areas 

 are connected with the phenomena. 



The migrations may take place in two directions: 



i) vertically, into higher water-layers not fished by the trawl, 

 2) horizontally, into other parts of the sea. 



- 120 



12 3 4 8 9 10 II 12 



Fig. I. Hake: northern North Sea, 1902 



A. 



12 3 7 8 12 



Fig, 2. Hake: northern North Sea, 1903 

 N.B. The figures i — 12 under the line represent the months (i ^January etc.). The figures alongside 

 the curves represents the average catch per day in pounds (Q = 0-5 kg. = ri lb. Eng.). 



It may be accepted, that both kinds of migration may participate in producing the 

 fluctuations in the curve of catches. We have therefore to ascertain if the facts given above 

 speak for the one or the other. In this I consider the data given as facts; the ascer- 

 tained agreement — almost astonishing in many cases — in the course of the curves 

 for the same region for two different years, as is shown in Fig. 1— 26 (p. 19—28), does 

 not permit us to consider the fluctuations due to mere change. 



According the position of the maxima in the various months, we can divide the 

 fishes into summer- and winter-species — as I have already done in a previous work'. 

 So far as the true North Sea is concerned, the division given there is a suitable classi- 

 fication. It will appear from the following, how far variations from it occur in the wider 

 region now considered. 



I) Henking, Die Befischung der Nordsee durch deutsche Fischdampfer (Mittheilungen des Deutschen See- 

 fischerei-Vereins, 1901, Nr. i). 



