212 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



frequent than ou the coasts of Stockholm and Oestgota, by the diftereut 

 direction of the wind prevailing daring the time when the heniugs come 

 near the coast. In the seventeenth volume of the Encyclopaedia Britan- 

 nica (last edition) the irregularities in the visits of the herrings to the 

 west coast of Scotland have, in accordance with the o^>inion of Pennant 

 and JIacCulloch, been exjilained by well-known changes in the Gulf 

 Stream, w^hich changes should cause the herrings, which always seek an 

 even temperature, to change their old places and seek new ones. This 

 opinion has recently been taken up by FranlBackkind. Prof G. 0. Sar^ 

 has finally endeavored to prove that periodical changes, connected with 

 the movement of the great herrings towards the north, probably take 

 place in the currents of the sea on the northern coast of Norway. He 

 thinks that these changes are indicated by the periodical occurrence of 

 wood, &c., washed ashore from foreign countries, and maintains that his 

 theory of the "herring-food" being found at ditferent times at different 

 distances from the coast presupposes regular periodical changes in the 

 currents of the sea. 



59. After haviug given the above historical review of the different 

 theories regarding the biological or physical causes of the periodicity of 

 the herring-fisheries, it remains for me to indicate the manner in which 

 I have further developed these theories during the last five years. I 

 started with an in^'estigation of the question, "Which fisheries are pe- 

 riodicall}" regidar, and which not"; and I have found that only very 

 large fisheries canied on near the coast and dei^endent on the propagat- 

 ing instinct of fish are periodically regular. From this I have drawn 

 the conclusion that it is the numher of a race of herrings which chiefly 

 causes them to periodically change their spawning-x)laces near the coast. 

 Other fisheries show irregularities with regard to the coming of the her- 

 rings, but no periods marked by a complete cessation of the fisheries and 

 ^J regular changes. Thus the Norwegian summer-herring fisheries owe 

 their existence to one or several large races of herrings ; but, as far as 

 known, they are not periodical. This seems also to be the case with 

 those fisheries which are carried on in the open sea at some distance 

 from the coast, where the fishermen follow the lierrings to their spawn- 

 ing-places. Oiu' knowledge of these herring-fisheries, however, is very 

 incomplete, for we know very little regarding the quality of the herrings 

 and the possible changes of time and place. 



The races (or schools) of herrings may nevertheless practically be 

 divided into large and small ones, the line between the two not being 

 very sharply drawn. And the very fact of certain races of herrings 

 being large has led me to explain the periodicity of the herring-fisheries 

 ui two diftereut ways, which I shall give below. 



60. The enormous numbers in which the large races of herrings make 

 their appearance must doubtless (especially when they select a limited 

 extent of coast for their spawning-place) produce a great change in the 

 natural condition of the coast- waters, both by their furnishing food to 



