96 



THE MIGRATION AND CONSERVATION OF SALMON 



I studied first in the Skagit River in Wash- 

 ington. 



Environmental conditions are clear in 

 such a stream; one finds the fish subject to 

 a few clearly evident stimuli which guide 

 the majority of their actions. The stimulus 

 which is most distinct is mechanical, the cur- 

 rent influence. The original study of Rutter 

 on the movements of salmon through estu- 

 aries, dealt with the adult red salmon or 

 sockeye. One recognizes that in estuaries 

 the influence of the tide twice a day is at 

 one period concurrent with the stream in- 

 fluence and at the other period antagonistic 

 to the river influence. Rutter observed 

 what I think has been seen since then by 

 numerous others that the fish go up with 

 the falling tide and turn out with the in- 

 flowing current. With each tide they go 

 further up and a less distance down the 

 estuary so that each tidal movement is up 

 and back part way which ultimately carries 

 them up stream beyond the tidal influence. 

 During this period one sees them milling 

 around at the turn of each tide when they 

 are observed in the eddies where the fish 

 actually act as if uncertain where they were 

 going. I have been much impressed by the 

 uncertainty of their movements at that 

 point. 



The influence of a current stimulus is also 

 demonstrated in their movements in fresh 

 water. So long as they are in contact with 

 a single current where the river is flowing 

 steadily without contributions from side 

 streams, they merely keep on moving. To 

 be sure in a river they do not move con- 

 stantly throughout the full 20 hours, but in 

 warm weather at least they rest in deep 

 pools during the periods of bright daylight. 

 They also move little at night, but start up 

 conspicuously in the early hours of morn- 

 ing twilight and go on upstream against the 

 current. 



In any large river it is difficult to observe 

 movements of the fish in the stream gener- 

 ally. One can see the salmon only at spe- 

 cial places as they pass over shallows or 

 barriers. In this way I have found that 

 the salmon apparently rest at night since 

 they did not use a fishway at all during the 



hours of darkness even though this fishway 

 was experimentally illuminated brilliantly 

 at night, during part of the period of 

 migration. 



The influence of light on upstream migra- 

 tion of adults was illustrated in striking 

 fashion by my observations at the Rock Is- 

 land dam on the Columbia. Local fisher- 

 men had reported that salmon did not use 

 the ladder which was well located and well 

 constructed. I started my observations at 

 the dam early in the day, indeed soon after 

 dawn and found the fish at that hour going 

 vigorously up the ladder and into the river 

 above the dam. The ladder is located at the 

 east bank where mountains almost at the 

 margin of the river shelter the water from 

 direct rays of the morning sun. The fish 

 kept running up the ladder in good num- 

 bers and without the least hesitation until 

 the sun's rays coming over the ridge struck 

 the water in the ladder. Then the salmon 

 run stopped almost immediately and not a 

 single salmon entered the box at the foot of 

 the ladder during the day time. Move- 

 ments in the afternoon began late, appar- 

 ently when the rays from the sun in the far 

 west were so oblique that the light was 

 totally reflected from the surface of the 

 water and when indirect illumination was 

 also reduced. Salmon entering the ladder 

 came out of deep water and on leaving went 

 down into deep water. 



The only place you could usually see the 

 salmon was in the ladder. The compart- 

 ments in the ladder were very large and the 

 space was generous; they went through the 

 boxes like a college hurdler, loping over the 

 weirs with perfect ease and then turning 

 like a flash at the top compartment and dis- 

 appearing through the gate into the river. 

 I have made all sorts of efforts to follow the 

 fish consistently in that river, above and be- 

 low that dam, but without success. They 

 appear now and then finning at the surface, 

 but one cannot follow constantly a particu- 

 lar fish. 



The same activity is shown on the Skagit 

 River, a much smaller stream where you can 

 see them clearly and follow them. They 

 move perfectly definitely up stream until 



