XXIII.-ON FISH-WAYS. 



By Chaeles G. Atkins. 



A— INTKODUCTOEY EEMAEKS. 



lu the present paper, it is jjroposed to discuss devices for facilitating 

 the ijrogress of fish over dams in their ascent only. The question of their 

 descent is by no means devoid of importance 5 but the difficulties and 

 dangers attending this stage of their migrations are of a totally diiferent 

 kind from those that assail them on their ascent, and are to be met by 

 a different set of expedients. Indeed, in most cases, neither the adult 

 fish nor the young requires any sort of assistance in descending. If there 

 is a sufficient body of water falling over the dam, they go with it safely 

 and readily, tumbling down from great heights and rarely sustaining any 

 injury. It is only where the peculiar configuration of the river and the 

 dam or the scarcity of water leads them into dangerous rocks or mill- 

 wheels that they require attention. The investigation of this branch of 

 the subject is therefore of less pressing importance than that of the 

 means of securing their ascent. 



B— HABITS OF MIGRATORY FISHES. 



Before discussing the mode of constructing fish-ways, it is necessary 

 to consider briefly the habits and peculiar traits of the several species 

 for whose use they are designed, so far as these habits and traits con- 

 cern the present subject. 



The only American species for which it has been thought expedient 

 to build fish- ways are the salmon, shad, and alewife. All three of them 

 ascend the rivers in spring and early summer in order to reach suitable 

 places to deposit their eggs. The salmon comes both earlier and later 

 than the other species, and proceeds immediately to the vicinity of its 

 spawning-grounds on the upper waters, where it lies in quiet pools until 

 the following autumn, its spawning-season. The shad comes while the 

 river is still in full volume, later than the earliest, and earlier than the 

 latest, run of salmon, and spawns within a short time of its arrival in 

 some gently-flowing part of the river. It neither ascends so far nor 

 pushes into so small streams as the salmon. The alewife, coming a little 

 in advance of the shad, but largely in company with that species, spawns 

 often in the still waters of gentle rivers, but more generally in lakes and 



