16 



ing, and in their weakened condition are less able to withstand 

 attacks of fungus and similar fresh-water affections. 



In the ponds both young and old alewives are subjected to 

 changes in food supply, oxygen content of the water, tempera- 

 ture and weather conditions. The artificial changes in the 

 rivers, streams and ponds resulting from the influence of trade 

 waste pollution plays an appreciable but as yet indeterminable 

 part in their life history and habits. 



Migration. 



Little is known of the history of the alewife after it descends 

 as a small fish to the ocean. Exactly where it goes and what 

 happens in the interval before its return is unknown, although 

 it probably frequents deep water. Even the extensive studies 

 of the habits and migrations of the sea herring, especially on 

 the Scottish coast and in the North Sea, have thrown little 

 light on this phase of the existence of the closely related alewife. 



The fresh-water cycle of the alewife's life is better known. 

 It approaches the coast at a definite period in the spring, mak- 

 ing its appearance in the vicinity of the Carolinas as early as 

 March, and later reaching the northern rivers. This sequence 

 does not prove a definite northward movement, but it indicates 

 that its annual migration is largely governed by the tempera- 

 ture of the water. 



After spawning the adult fish returns to salt water in a lean. 

 emaciated condition. Whether these fish spawn but once or 

 continue to spawn annually has not been determined. The 

 experience of commercial observers indicates that they probably 

 spawn but once. If the same fish spawned repeatedly the 

 fishery would enlarge beyond our most favorable dreams, and 

 fluctuations in the annual catch would not exist. 



Ascending Streams. — Current appears to be the stimulating 

 factor in the ascent of streams. In a rapid flow, progress is 

 almost continuous, but in more quiet waters, such as pools or 

 eddies, for no apparent reason, the fish may remain in one local- 

 ity, darting forward, falling back, shifting position, or lying 

 quietly in the stream, but making no appreciable headway. 

 Then one fish, usually a female, takes the lead, closely followed 

 by several males, the entire school trailing along behind, and 



