For reasons no one completely understands, fish ladders and elevators are not helping fish at some mainstem dams in the East.
Scientists and engineers set targets for the transport capacity of fish passages. And yet, the study lays bare that those targets are being missed by orders of magnitude. For instance, the first Merrimack River dam aims to let 300,000 river herring pass through; the mean number for the years 2008 to 2011 was 706 per year. The goal at the first Connecticut River dam is 300,000 to 500,000 fish. There, the mean for those same years was 86. And for the Susquehanna, the goal is 5 million river herring spawning above the fourth dam, which passed an average of seven herring from 2008 to 2011. This means that very few fish are reaching quality breeding grounds, which has likely contributed to the decimation in river herring populations.
LINK (via:Science)