of the Fishery Board for Scotland, 



53 



side of the pass ; and 2n(l, the width of the pass is less than six feet, 

 althougli the length of the djim is more than 200 feet. 



With regard to the position of the foot of the pass, its projection 

 beyond the toe of the dyke is a very great defe(^t. For, as pointed out by 

 Mr. Atkins in his report " On Fish-ways," in ascending a river sjxlmon 

 follow^ the main stream until met by an obstruction. At the foot of 

 this they swim to and fro trying to ascend. If unsuccessfid, they will 

 after a time drop back to the nearest pool to rest. But on their next 

 attempt they will again ascend to the foot of the obstruction, to be 

 again baffled, and thus repeatedly pass the mouth of a ladder which 

 enters the river belo\v the obstiuction without noticing it. In con- 

 structing a fish ladder, therefore, one of the chief objects to be aimed at 

 is to place the eiitrance at the furthest i)oint to which the fish can reach 

 in their ascent of the main stream. An attempt has been made to 

 remedy this defect by placing stones on the north side of the pass so as 

 to form a lead for the fish. This expedient may modify the injurious 

 results of this defect when tlie river is low, but is not of much use when 

 the river is at a medium or high level and the fish most inclined to 

 travel. On the 16th and 18th October, when eight to fourteen inches 

 of water were flowing over the crest of the dam, salmon were collected 

 in large numbers in the pools higher up than the entrance to the pass, 

 from which they were attempting to ascend the face of the dam, but it 

 was only on the north side that they were ever successful. 



With regard to the width of the intake, it may be stated generally 

 that the larger the volume of water in the pass, provided it does not 

 cause too great turbulence in the chambers, or too great resistance to 

 the fish, the more will fish be attracted to it. No benefit, however, 

 would be derived from widening the intake if its depth were reduced. 

 On the contrary, if the volume of water is not increased, it is better 

 that the intake should be narrow and deep than broad and shallow, as 

 it admits of the ladder being supplied with water at a lower state of 

 the rivei*. 



In considering whether in other respects the fish-pass afibrds a free Whether in 

 passage for salmon, and, if not, wherein it is defective, I propose to ''j^^^^^rj^P®^^^'^ 

 point out, 1st, the principles generally aimed at in the construction of affords a free 

 fish-passes, and the causes of failure in application ; 2nd, the defects of i):iss for Salmon 

 construction in Craigo fish-pass ; and 3rd, the opinions expressed as to 5J^J|^^j.gjjf ^^^f^ 

 its efficiency by those present at the inspection. defective. 



] St. Now% it is well known that the further a falling liody descends 

 unobstructed the greater the force it attains, and in order, therefore, 

 that water descending from a height, at a steep gradient, may not 

 off'er too gi-eat I'esistance to fish, it is necessary to check its velocity at 

 frequent intervals. Numerous systems have been devised for breaking 

 the force of the current in a fish-pass without causing too great dis- 

 turbance of water. There are Smith's, Forsyth's, Atkins's, Brackett's, 

 Oail's, Forster's, Swazey's, Pike's, Roger's, Hockin's, and many other 

 ^jystems. These systems, which differ in many respects, have, as a rule, 

 one feature in common — viz., that whenever the gradient is as steep 

 as one perpendicular to ten hoi-izontal, the openings in the stops and the 

 width of the pass beai- such a proportion to one another that, when the 

 pass is in working order, a cushion of quiet water is secured in each 

 chamber against which the descending current expends its force before 

 passing on to the next chamber. But although numbers of these passes 

 have been erected, but few of them — probably not more than half a 

 dozen — have proved effective. Their non-success seems due to the 



