FISHES AND MANKIND 413 



the passage of the fish over or round the obstacle, but the 

 expense incurred has prevented this from being done in many 

 cases, and it seems certain that stringent legislative measures 

 will have to be taken if the stocks offish are to be saved. 



The most serious obstacle of all to the welfare of fresh-water 

 fishes, and one which provides an all too effective barrier to the 

 ascent of Salmon and Sea Trout, is the wholesale pollution of 

 the rivers which has been going on practically unchecked tor 

 a long time. The development of certain industries has reduced 

 the water in some of the rivers to a terrible state, and crude, 

 untreated sewage, the poisonous effluents of steel and iron 

 works that manufacture by-products, from sugar beet and 

 ardficial silk factories, chemical works, collieries, mines, and 

 the like, are being poured into our rivers and streams in ever- 

 increasing quandties to poison or asphyxiate vast numbers of 

 fishes and other forms of animal life. Fortunately, the outlook 

 is not hopeless, and a vast amount of research and inquiry 

 is now being carried out as to the best methods of dealing with 

 this menace. A great deal of unnecessary pollution is due solely 

 to ignorance or indifference on the part of factory owners and 

 local bodies, as there are comparatively few waste products 

 that cannot be dealt with scientifically and their harmlul 

 eflfects minimised. "The country is waking up to the fact, 

 writes Mr. Calderwood, "that growth in industry does not 

 necessarily mean the fouhng of our rivers, and manufacturers 

 and others responsible for the present state of aflfairs are realising 

 that public opinion is against them if they persist in their 

 inattention to the needs of river purification. . . . Another 

 form of commercial undertaking that provides a new menace to 

 the fisheries for Salmon and Trout is the development of hydro- 

 electric schemes, which means the building of large dams, the 

 alteration of water-courses, and changes in the volume of water, 

 to say nothing of the damage done to the spawning grounds. 

 The Salmon rivers of the Pacific coast of North America have 

 been pardcularly affected by such undertakings for a number 



^ Among minor contributory causes to the decline in the stocks 

 offish, mention may be made of the depredations of otters and 

 fish-eadng birds, and of human poachers, but these are un- 

 important in comparison with those dealt with above. 



The subject of fish diseases is worthy of some consideration 

 for there are certain contagious maladies that play havoc with 

 the stocks of fresh-water fish and constitute a serious menace 



