Many years ago, I read the results of surveys on the impact of new smallmouth bass populations on salmon populations in Washington State. The results were that five of the ten rivers surveyed showed no difference in salmon returns and five showed an improvement, although some improvements were quite slight. I rationalized that the five streams showing an improvement in the salmon runs were rife with squawfish (now called pikeminnows). But I never called or followed up with a request for more exact information.
More recently (by far), another survey has dealt with smallmouth bass and salmon, in this case Atlantic Salmon, interaction. The study showed that there is very little interaction between smallmouth bass and juvenile Atlantic Salmon in Maine. The smallmouths tended to reside in slower-moving sections of the rivers surveyed and did most of their feeding during the daylight hours. The smolts, on the other hand, tended to hold in swifter sections of the rivers – usually in shallow riffles and did much of their feeding at night. So the interaction between the two fish species was rather minimal.
However, during late summer and early fall when stream flows were much reduced and water temperatures much warmer, the the lines between the most active times and holding water of the two species blurred and the salmon smolts became more susceptible to predation by smallmouths and the two species competed more directly for food and holding areas.
The recommendation that came out of this study was that fisheries personnel for the state of Maine should focus their best efforts on salmon recovery programs on waters that do have smallmouth bass.
When I read the results of this study, I immediatley felt that the results fit the Umpqua River “to a T”. The Umpqua gets very warm in the late summer and early fall months and both adult salmon and salmon smolt often appear impaired. While fishing out of a float tube type device that only reaches several inches beneath the river’s surface, I have been rammed several times by salmon blindly, but instinctively swimming upstream. It would seem to make sense that the salmon smolt would also be affected by the warm water temperatures to the point where they be far easier prey to smallmouths large enough to eat them or less competitve with smallmouths that they would normally be competing for food with.
In the spring when the Umpqua River flows high and cool, I have seen a ten inch rainbow trout repeatedly and easily elude a 16-inch smallmouth in a narrow backwater in the Tyee area. The ease with which the trout avoided the smallmouth’s best efforts at eating it convinced me that in cool water situations, salmonid predation by smallmouth bass would be greatly reduced from when the water temperatures are high enough to impair the trout and salmon smolts.
The implication of the Maine survey is that it is extremely important to try to avoid activities that result in reduced stream flows and increased water temperatures – especially in waters that hold salmon smolts or trout and smallmouth bass.