Now, I do not claim to be as knowledgeable as basically any fisheries biologist, but being that I have spent a lot of time looking into the subject and a pretty substantial amount of time fishing and observing the Connecticut River watershed I think I have at least a reasonable understanding of the fishery. I have also learned, through the work of others, about similar cases involving both salmon and other anadromous salmonids. Take this for what it is, an angler's view of the decline of one of the greatest sport fish to swim in CT waters.
People are without a doubt the most destructive and dangerous animal to ever live on God's Green Earth. And there may be no period of time when humans had less concern for the Earth then the industrial revolution. In CT nearly every body of water large enough was dammed, cutting off valuable spawning ground in nearly every river salmon ran up. The last naturally spawning salmon recorded in CT waters occurred during the Civil War.
To the common fishhead, the dams may seem to be he main culprit. On closer examination that is clearly not the case. Initially, when the salmon restoration began, there were some substantial returns to the rivers. But as time progressed fewer and fewer salmon came back despite many juveniles being stocked. Even in a year with terrible flows and temperature, like 2015 and '16, substantial numbers of salmon parr prevailed. I have fished the Salmon river in September before the fall trout stocking and caught as many as 50 salmon parr in a less than a half mile of river. And in the spring I catch numerous silver smolts in all parts of the watershed. What then happens to these smolts? I suspect a similar situation is now being played out in the Maritimes, where striped bass not traditionally found that far North are being blamed for the consumption of outgoing smolts. Mind you, I'm not suggesting that striped bass were not common in the Connecticut River when salmon runs were more sustainable. There were certainly more of them "back in the day". The variable that has changed here is the available forage. Herring and shad, which were historically frequent in the same region, are depleted so dramatically that they have ceased to provide the striped bass with the food they look for during their spring migration. Despite the dramatically low herring returns, striped bass still stack up at the mouths of rivers in he spring, at the same time that thousands of bite sized salmon smolts are migrating out. Just as the loss of eel grass has left sea run brook trout at the mercy of striped bass and bluefish, the lack of large quantities of fat-rich herring has left salmon smolts at the mercy of the same predators.
It is no secret that man of the fish swimming in the Connecticut River watershed are far from their native range. Smallmouh and largemouth bass, as well as brown and rainbow trout, eat numerous juvenile salmon each year. I have caught four large smallmouth in the Salmon River that either had a live salmon parr in their throat or coughed up dead ones. After the spring stocking of juveniles I catch stocked trout, fish that would not often naturally reach their size in such small streams, that have bellies full of fry and parr. If there is any issue that is directly related to the rivers themselves, this is it. In Alaska this issue has been identified by fisheries biologists. Invasive pike are directly effecting the salmon returns.
As far as what happens once the smolt get out of the river, I don't know. I could speculate on it all day, but the ocean is a place I have not studied near as much as the rivers that I live very close to. But what I do know is that most biologists think the biggest cause for low salmon returns throughout the North Atlantic is not in the rivers themselves but in the oceans, and that these causes are nearl impossible to reverse. And I know that with the current situation there is not much hope for the future of Atlantic salmon in CT, or anywhere else in the US for that matter. It is truly a tragedy that this may well end up being the last, or one of the last true adult anadromous salmon caught by an angler in the Salmon River: