East Coast Fish are Stupid

Herring Unable to Find Fish Ladders on East Coast Dams

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.
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It's not like fish ladders never work. American shad climb ladders in Western U.S. rivers with apparent ease, says co-author Karin Limburg, a shad expert at the State University of New York's College of Environmental Science and Forestry in Syracuse. But for reasons no one completely understands, they're not helping fish at these mainstem dams in the East. Many fish have trouble finding the passages in these large waterways, Limburg says.

I guess all the smart ones were moved to the West Coast, since American  Shad were introduce to the West from Eastern populations.