I have no photos but I have eye witness accounts. They can haul themselves over some obstacles.
“With an acute understanding of physics, the alewives turn on their sides and swim sideways up the ledges to maximize the surface area of their tails against the current and then right themselves as soon as the water gets deeper. When the current is hard they will swim so fast they shoot out of the water, not to jump, but because their momentum carries them out of the water and into the air”
Watts, Douglas. Alewife. Augusta: Poquanticut Press, 2012. pp. 12-13.
Sandy, alewives are very capable swimmers. They are not considered jumpers (i.e. salmon) however they will jump on occasion. If there is a hydraulically plausible path over or around an obstacle, the alewives will find it. Will all make it? No, the more difficult the obstacle (man-made or otherwise) the fewer fish successfully make it through. On longer reaches this can have a “compounding interest” result e.g. 25 mile stream. Beaver dams, cascades, tree fall etc. 1,000 Alewives come to obstacle #1 90% make it past = 900. 900 alewives make it to obstacle #2 and 86% make it past = 774. 774 alewives come to obstacle three, a low head beaver dam and only 50% make it over = 337. So from 1,000 to 337 in only three obstacles. Each scenario is unique depending on location and other abiotic factors such as flows & temperature. The old Edwards dam site on the Eames Road in Benton is a prime example. You’d swear that no alewife would make it over but they do. Just not in uninterrupted droves were it just a “plain” low grade stream course with a well-defined thalweg. These obstacles can also effect sex ratio. Males seem to be a little more capable than gravid females. So, potentially fewer females might go on to spawn thereby impacting juvenile recruitment and subsequent adult recruitment four years down the pike.
FULL DEFINITION OF THALWEG
1a : a line following the lowest part of a valley whether under water or not
b : the line of continuous maximum descent from any point on a land surface or one crossing all contour lines at right angles
c : subsurface water percolating beneath and in the same direction as a surface stream course
2 : the middle of the chief navigable channel of a waterway which constitutes a boundary line between states
Origin of THALWEG
German talweg (formerly spelled thalweg), from tal valley (from Old High German) + weg way, path, from Old High German — more at dale, way
Nate Gray
John Hay The Run p. 37
Everything Eats Alewives 