Fishes of the Western North Atlantic 489 



generally to gravelly ripples where the degree of bottom silting determined the amount 

 of shelter. 



Measures necessary to improve streams for Atlantic Salmon include: better land- 

 use practices to reduce erosion, floods, and low summer flow; overcoming pollution 

 and the detrimental effects resulting from measures undertaken for the benefit of other 

 resources (e.g. spraying forests to control injurious insects); and means of assuring 

 reproduction in streams used in the development of hydroelectric power or irrigation. 

 The cost involved in adopting remedial measures will determine the extent to which 

 suitable streams will be saved for Atlantic Salmon production. If society values this 

 species highly enough, its future can be assured through wise management based on 

 research. Overcoming pollution, for instance, is largely a matter of deciding on the 

 relative importance or value of Atlantic Salmon compared with the value of industries 

 that cause pollution. If the cost of disposing of polluting substances by means other 

 than putting them into streams will be greater than the value placed on the fishery, 

 then the latter will be sacrificed; and, in considering the worth of this species, values 

 other than those of economics must be considered, such as the sports value. 



In the past, relatively too much emphasis has been placed on restricting the catch 

 and too little on maintaining suitable stream conditions. Recent studies indicate that, in 

 many streams, enough spawners escape capture to provide all the young that can 

 survive and grow in the streams in their present condition (^2). That this number is 

 not large is shown by the results of studies in four streams of the Maritime Provinces, 

 where it was found that between 40 and 50 pounds of adult females per mile of stream 

 10 yards wide are enough to maintain stocks (^j: 23). 



The role of hatcheries in maintaining Salmon populations is not as great as it once 

 was believed to be, but hatcheries have an important place if the young fish produced 

 in them are used intelligently. If the eggs normally deposited by the adults at the 

 spawning grounds are adequate to produce all the young that can survive and grow in 

 the stream, the planting of more young is not only wasteful but may actually be harm- 

 ful by increasing the competition for limited living room and food. However, in 

 streams that lack suitable grounds but where conditions are suitable for the survival 

 and growth of young to the smolt stage, the planting of hatchery-reared young may 

 be beneficial. Also, in streams barred by dams over which it is not practical to pass 

 spawning adults, the planting of hatchery-reared young may be advantageous if means 

 can be provided for them to reach salt water. Where the use of streams by adults and 

 young has been made impossible, a fishery may be preserved by raising young to the 

 smolt stage under artificial conditions and planting them directly in an estuary or in 

 the sea. Another promising method of providing artificial propagation is in creating 

 artificial spawning beds to replace those eliminated by power development or other 

 detrimental factors. 



In Sweden the experimental planting of marked smolts has given a return of 5- 

 10 "/o in adults, a higher percentage than is usual; this suggests that artificial propa- 

 gation may be sound both biologically and economically {32). Efforts to rehabilitate 



