46 



THE CAUSES OF DECLINE. 



While in some streams the alewife fishery has held its own, 

 or even improved; it has diminished in others to such an ex- 

 tent that we can accept the general statement that there has 

 been a serious decline. With the increasing prices and the de- 

 velopment of artificial fisheries, production statistics give but a 

 partial view of the situation, which can be obtained only by an 

 intimate knowledge of each stream. The harmful effect of this 

 decline upon the shore fisheries has already been explained, and 

 few more convincing arguments can be advanced in favor of 

 replenishing all possible alewife streams than its influence upon 

 the future welfare of the shore fisheries of Massachusetts. 



The causes which have contributed to this condition are so 

 numerous and so complex that the separate influence of each 

 cannot be absolutely determined. Both natural and artificial 

 changes have brought about this decline, although the latter 

 are by far the more destructive. Four prominent causes are: 

 (1) destruction of the spawning grounds; (2) obstructions 

 which prevent the alewives from passing to the spawning 

 grounds; (3) pollution of streams; and (4) overfishing, the 

 result of unwise regulation. 



Destruction of Spawning Grounds. 

 Many alewife streams which once were important can never 

 be restocked because their former spawning grounds are no 

 longer available. Among the various upheavals resulting from 

 natural causes may be mentioned the lessened volume of water 

 as a result of extensive deforestation, changes in the location 

 and form of the outlet, and lowering of the water level in the 

 ponds. The extensive cutting of forest land has altered the 

 water flow in certain streams. ' Forests act as huge absorbent 

 blankets, which catch and retain the rainfall. Without this 

 protection the rainfall passes quickly into the streams causing 

 soil erosions and heavy freshets, and streams in which alewives 

 once could easily ascend to the headwaters become diflftcult of 

 access. The lowering of the water level through natural agen- 

 cies, of less frequency than artificial means, may result in a 

 new outlet or a permanent closure. 



