1867.1 129 [Lyraan. 



The^hief cause of the decrease of migratory fish has been the 

 building of impassahle dams. To obviate this difficulty, the construc- 

 tion of fish-ways has become necessary ; and we find that there are a 

 dozen conditions which a fish-way, be it small or great, must fulfil, 

 to wit : that a good channel lead up to its lower end ; that the lower 

 enil be so placed and arranged that fish easily find it ; that the head be 

 so placed as to be easily found when the fish again pass down the river; 

 that the lower end, and the whole course, be wide enough ; that the 

 ascent be not too steep ; that tjjere be a sufficient sheet of water fall- 

 ing down it ; that the supply of water be properly regulated at the 

 head ; that it be protected from destruction by falling ice', by freezing 

 up, by floating timber, and by freshets ; that the water above and be- 

 low be practically pure ; that it be protected from poachers ; that it 

 be not placed near machinery that might scare away the fish ; that 

 no fishing be allowed within four hundred yards of its upper and its 

 lower end ; and finally, that it be kept open at all times when the 

 migratory fish are passing up the river, or are returning down the 

 . river. 



Fish-ways may be made in two modes : the pass, which is simply 

 a sloping trough, or the stair, which is a series of steps, whereof each 

 is a water-tank. In the first case, the fish rush up the sloping trouf^h ; 

 in the second, they jump from step to step, aided by the flowing sheet 

 of water, which makes a series of little falls in its descent. The pass 

 is more simple, cheaper, and less likely to get out of order ; but the 

 stair gives better chances to the fish to rest in their ascent, and is, 

 therefore, more fitted for high dams, and for fish of less activity than 

 the salmou ; for example, the shad. Several modifications may be. 

 introduced in the construction of both. Where a pass is of consid- 

 erable length, it is necessary to nail to its floor, cross-cleats, or bulk- 

 heads, which run from and at right angles to the sides of the trough, 

 about two-thirds across it, leaving the remaining third open. These 

 bulkheads are arranged alternately, so that the open space comes first 

 on one side of the trough and then on the other ; thus the water, 

 running down, strikes the bulkheads, and is constrained to pursue a 

 spiral course through the alternating openings. In this way the speed 

 of the water is checked, its course made longer and less steep, and 

 a series of eddies is formed, below the bulkheads, wherein the fish 

 may rest. Other modifications will suggest themselves ; an addi- 

 tional set of bulkheads may be inserted, at right angles to the first, in 

 such a way that the water must run first forward ; then to the right ; 

 then forward ; then to the left; then forward again, and so on. In 

 the stair, the first modification of a simple line of tanks set step- 

 fashion, and pouring from one into the next lower, is to make one- 

 half of the outer lip of each tank lower than the other half, so that 



PROCEEDINGS B. Si N. H.— VOL. XI. 9 JUiY, 1867. 



