96 American Fisheries Society 



mined. Four prominent factors are (1) destruction of the spawn- 

 ing grounds, (2) obstructions which prevent the alewives from 

 passing to the spawning grounds, (3) pollution of streams, and 

 (4) overfishing. 



Destruction of Spawning Grounds. — Many alewife streams 

 which once were important can never be restocked because their 

 former spawning grounds are no longer available. Some have 

 been taken for water supplies, screened, and the original outflow 

 diverted. Natural agencies and artificial changes such as drainage 

 and deforestation have altered spawning grounds and streams. 



Obstructions. — One of the first steps in the development of a 

 fishery is the removal of all obstructions to give free access to the 

 spawning pounds. Natural changes may alter the course or flow of 

 streams in such manner as to prevent the passage of fish. Natural 

 or artificial falls, dams, unless equipped with fish ways, and material 

 of various kinds prevent or make difficult the passage of alewives. 



(1) Dams. — Dams are the inevitable result of the inroads of 

 colonization following the waterways. In former days water power 

 was even a greater necessity than in the present era of coal, gas 

 and electricity. As manufacturing became of greater moment, 

 more water power was required, and eventually numerous dams 

 were erected upon the streams of Massachusetts. The mere 

 presence of dams is not dangerous. Only when they are unequipped 

 with fishways or are not opened during the spring run do they 

 become a menace. Properly supplied with adequate passageways, 

 dams would never have exerted a pernicious influence upon the 

 alewife fishery. 



(2) Cranberry Bogs. — A water supply is essential for the suc- 

 cessful operation of the cranberry industry, and in southern 

 Massachusetts numerous bogs are found along the alewife streams. 

 The cranberry industry affects the alewife fisheries by: 



(a) The erection of small dams usually not equipped with 

 fishways, the owners of which are supposed to raise their sluice- 

 boards during the annual run. However, at certain seasons for the 

 welfare of his bog, the owner may find it desirable to have the 

 water remain for a longer period, and thus block the progress of 

 the fish. 



(b) Changing the course of the stream by ditches and canals 

 which are inferior to the natural channels. 



