Salmon restoration on Penobscot a long-term process

Yesterday’s headline in the New York Times was pretty clear:  “Taking Down Dams and Letting the Fish Flow.”

In the article, my one-time striper fishing buddy Murray Carpenter reported on the startling recovery of Maine’s Penobscot River after the removal of two large dams and construction of a fish bypass around a third.

Three years after the river was re-opened, the fish are back.  

Shad Rips was uncovered by the Great Works Dam removal, and this year nearly 8,000 shad returned, along with the shad fishermen.

Also returning were more than a million alewives.  Endangered shortnose sturgeon were seen above the head of tide for the first time in more than 150 years, as were sea lampreys rooting in Penobscot gravel to lay eggs.

But what about the salmon? When can we fish for them again?  

They’re back too, with more than 500 counted at the Milford Fish Lift at Milford Dam this year. But salmon recovery is less dramatic than many of the other species and we expect it will take longer to see salmon numbers build.  

The rapid recovery of alewives, shad, lampreys and other native fish is a necessary step on the road to salmon recovery.

One of the driving concepts behind the Penobscot restoration was the realization that salmon co-evolved with other species, and that restoring salmon requires restoring the full complement of native sea-run fish.

A 2006 paper in Fisheries made a strong case that other species provided important ecological functions, and that “Restoring the co-evolved suite of native diadromous species to levels that sustain these functions may be necessary for successful recovery” of salmon.  

Those ecological functions are things like feeding predators — or, as the scientists put it, providing “prey buffers.”

For more than a century, Penobscot River predators such as cormorants and striped bass have feasted on salmon smolts dropping out of the river in May. Those smolts were easy pickings in a river with few other fish.

That predator-prey dynamic changes a lot when more than a million herring return to the river just as smolts migrate out, providing predators with a large, schooling, high-fat target.  

A month later, when otters and seals could otherwise key on returning adult salmon, shad -- whose Latin name “sapidissima” literally means “savory -- show up.

In the fall, when spawning salmon in shallow riffles might make for easy pickings in the headwaters, out-migrating juvenile alewives, shad, and river herring attract predators to the lower river.  

This video from Maine’s Department of Marine Resources shows the feast a restored alewife run means for striped bass in the fall as they feed on juveniles migrating to the sea.

Other benefits include spring-spawning lampreys cleaning spawning gravel for fall-spawning salmon and upstream transport of marine nutrients to headwater habitat in the bodies of millions of lampreys, herring and eels.

In the meantime, the spring shad fishing is a great fun. A 3-inch Deceiver on a 9 weight is a good choice for those fall stripers. And hopefully, as the river recovers, we’ll be back to casting for salmon soon.

Jeff Reardon oversees Trout Unlimited's efforts in Maine.