Mechanical and Electrical Weirs
Mechanical weirs were constructed on streams or small rivers in an early attempt to block spawning sea lampreys. The weir was constructed of hardware cloth (wire mesh) on a v-shaped frame (the point of the "v" is upstream) which directed fish and sea lampreys toward a trap. A wire mesh trap with a cone entrance allowed sea lampreys and fish to enter and prevented their escape. Spawning fish were transferred upstream of the weir, while sea lampreys were destroyed. Debris would often clog the wire mesh of the weir creating a dam-like effect which could either collapse the structure or cause flooding around it. Eventually, the mechanical weirs were replaced by electrical weirs.
Mechanical weir and trap (Photo by U.S. Fish & Wildlife Service staff)
Electrical weirs were constructed on large rivers to block spawning runs of adult sea lampreys. There were two arrays (DC and AC current) of electrified rods that were suspended into the water to direct fish and sea lampreys toward a trap or to stun them if they attempted to pass the weir. Spawning fish and sea lampreys were captured in an wire mesh trap with the sea lampreys being destroyed and other fish passed upstream. Electrical weirs were hampered by the loss of power or floods which either destroyed the weir or allowed sea lampreys to pass around the weir. Occasionally spawning fish would try to swim through the electrical field and would be either killed or deformed. The last of the style of electrical weir shown in the photo was removed in 1979. Recent attempts at developing more effective and dependable styles of weirs were conducted in cooperation with the State of Michigan.
Electrical weir and trap (Photo by U.S. Fish & Wildlife Service staff)
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