THE SALT-WATER FISHERIES OF BOHUSLAN. 209 



been driven away by the increased number of fish-of-prey and birds-of- 

 prey. This originally popular explanation is quite old, and has been 

 mentioned in a somewhat fault-finding manner by Diibh, and has been 

 attacked by Axel Boeck, but has, nevertheless, quite recently (in the 

 "Book of Inventions") found a scientific champion in Prof. F. N'. Stnitt. 

 He expresses himself regarding the causes of the periodicity of the her- 

 ring-fisheries as follows : "In all probability it is chiefly to be sought in 

 the common occurrence that when a race of animals which serves as 

 food for others, under peculiarly favorable circumstances increases in a 

 very marked degree, it also attracts more enemies, which increase in 

 number in ijroportion as the quantity of their food increases. The 

 weaker gives way to the stronger ; the herrings, therefore, seek new 

 spawning-places which afford better protection. When on the other 

 hand the fish-of-prey and birds-of-prey do not find the same quantity of 

 food, they diminish in number. If, therefore, a new race of herrings 

 comes to the old spawning-place and again finds its condition favorable, 

 they may increase at a very rapid rate." According to this explana- 

 tion all herring-fisheries ought to be periodical, for there is scarcely a 

 region where the herrings are not exposed to enemies ; but such a com- 

 plete periodicity as is here spoken of will only be found with very few 

 herring-fisheries. Nor do we find in any fishery-period an uninterrupted 

 increase in the number of the enemies of the herrings. Thus there 

 were rich shark-fisheries on the coast of Bohuslan immediately before 

 and in the beginning of the great herring-fisheries of the sixteenth cen- 

 tury ; and it is well known that in Scotland and other places the sharks 

 and other powerful enemies of the herrings are very irregular as to the 

 number in which they occur ; this is easily explained, as they cannot for 

 their food rely entirely on the herrings, which only visit the coast for a 

 short time every year, because they need rich food all the year round. 

 Very erroneous ideas seem to be entertained quite generally regarding 

 the occurrence of fish-of-prey during coast-herring fisheries, and their 

 dependence on such fisheries. These fish-of-prey, which otherwise are 

 scattered over a large area, gather in dense schools during the herring- 

 fisheries, and are, therefore, noticed more than at other times. Some of 

 these fish-of-prey chiefly depend for their food on the fisheries, and the 

 herrings are by no means as easy a prey as is generally supposed. It 

 will, therefore, be clear, that according to this theory the enemies of the 

 herring ought to increase in proportion as the mass of herrings increases, 

 whereby the herrings would again decrease. This generally takes place, 

 so that the unusual increase of one or the other kind of fish is soon neu- 

 tralized again. If, therefore, an increase in the number of fish-of-prey 

 were the cause of the herrings moving away from the coast, some cause 

 ought to be assigned explanative of the very strange disturbance of the 

 natural balance between the number of herrings and that of theii- ene- 

 mies. And this cannot be done, at least if Professor Stnitfs supposition 

 is correct, that when the herrings under favorable circumstances increase 

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