THE SALT-WATER FISHERIES OF BOHUSLAN. 217 



ing-place for a great race of herrings wliich are accustomed to si)awn iu 

 winter, would be another reason for opposing the idea tliat the Nor- 

 wegian spring-herrings had alternated their visits between the coast of 

 Bohusliin and the west coast of Norway.**^ 



06. For the sake of comparison and coini>leteuess, we nmst also give 

 an account of those circumstances which haxe been assigned as the 

 causes of the disappearance or diminution of fish in localities where they 

 liave been observed for a long time. Among the causes which have been 

 mentioned, the following are the principal ones: Ujndemics among the 

 fish, changes in the nature of the icater or of the bottom by volcanic erup- 

 tions or by the accumulation of mud (caused, among other things, by the 

 increased denudation of the coast consequent upon the destruction of 

 the forests), and steamboat traffic. 



In carefully examining the rich literature on this subject, it will be 

 found that of all the causes which have been mentioned as having an 

 injurious influence on the fisheries, only the following have been more 

 generally accepted: Excessive fishing, fishing with destructive apparatus^ 

 destroying the vegetation of the bottom, the eggs, and the young ones, 

 'preventing the fish from reaching their spaivning-places, impure or turbid 

 rcater, fish-ofprey, and, finally, lack of food [whicli may be caused by 

 human agencies). 



Among those fish whicli, like the herrings, have either entirely or to 

 some extent left places where formerly they have been very common for 

 longer or shorter periods, we may here mention the following North Sea 

 fish: The codfish, the haddock, the mackerel, and the shark. On the 

 northeastern coast of America there are a number of fish of which the 

 same is known. It thus appears that just the most important sea-fish 

 are quite irregular in their coming and going, and, unfortunately, our 

 knowledge of the causes of this phenomenon is exceedingly limited. 

 Not only our scientific but also our historical knowledge of these fish, 

 and especially of the herrings, is so limited that at x>resent there is very 

 little hope of having this scientific problem satisfactorily solved in the 

 near future. Such a work requires not only a most extensive biological 

 and i)hysical knowledge of our waters, but also a thorough acquaintance 

 with the history of the different fisheries. It is greatly to be lamented 

 that Axel JBoeck^s premature deatli put an end to the important study of 

 the history of the Norwegian herring-fisheries, to which he had devoted 

 himself for several years, and that the rich material which he had col- 

 lected for a history of the Scotch and Dutch herring-fisheries has not 

 been worked up. It is quite likely that this material, properly worked 

 up in a scientific manner, would furnish many and important contribu- 

 tions towards the solution of the problem regarding the migrations of 

 the great races of herrings. 



8' It is entirely different, however, with those sea-herrings that visit the coast of 

 Bohuslan or the west coast of Norway during winter for other purposes than spawning. 



