Fish Ladders – A Step Up But Not Always Over

Sean Mahoney | @SeanCLF

Counting Alewives at the Milltown Dam fishway on the St. Croix river in New Brunswick, Canada, Photo courtesy of the Portland Press Herald

Fish ladders and elevators “aren’t working like they’re supposed to, and fish aren’t making it to where they need to go.” So began a recent article in Science magazine. In many cases this assertion is spot on – but in others, fish passages have been remarkably successful. Maine has examples of both.

To find a faulty fish passage,  one need look only at the dam on the Androscoggin River between the towns of Brunswick and Topsham, Maine. The fish ladder at that dam quite simply does not work and the number of fish that successfully navigate its labyrinth is paltry. If anadramous fish like salmon, shad or river herring are ever to return to the reaches of the Androscoggin, significant changes will need to be made to that fish ladder. Better yet would be, where possible, the removal of dams through collaborative efforts like those that led to the success of the Penobscot River Restoration Trust’s efforts or the removal of the dam in Winterport several years ago.

On the other hand, fish ladders remain an important management tool in areas where dam removal cannot be achieved. Indeed, there are a few fish ladders that have been very successful at passing fish, especially when they are allowed to work. For example, in Maine fish ladders at the first three dams on the St. Croix River worked remarkably well – in just 5 short years of operation in the 1980’s, the number of alewives successfully surmounting the 3 dams via fish ladders went from 20,000 to more than 2.5 million. And in 1995, when, for reasons that had nothing to do with science or logic, a state law was passed closing two of the fish ladders, the number of alewives plummeted to less than 1000. Today, even after one of the fishways was allowed to be opened in 2008, alewives are still barred from 98% of the waters that they use to spawn. That’s why CLF will continue to fight to repeal that law, either through the Courts or with our allies in the Legislature.

That said, the data provided in the Science article is depressing. At three major rivers on the East Coast that less than 150 years ago had been teeming with anadromous fish – the Merrimack, the Connecticut and the Susquehanna – virtually no fish –  706, 86, and 7 respectively – passed through the fish ladders at those dams. The author’s call to remove those dams would no doubt increase those numbers significantly and should be pursued to the extent feasible. Alternatively, the fish passage at those and other dams should be evaluated as to effectiveness and those that fail as miserably as those on the Merrimack, Connecticut and Susquehanna, as well as the Androscoggin, should be repaired, modified or replaced with fish passage that does work, like that on the St. Croix.

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