Catadromous is a biological term most of us don't use everyday. It applies to fish, like American eels, that spend most of their adult lives maturing in fresh/estuarine water and then head out to the open ocean to spawn. Actually, the female American eels (Anguilla rostrata) are the ones that come far upriver, often spending decades well inland while their male counterparts lurk in brackish waters. This life cycle is the reverse of anadromous species like herring, shad and salmon that breed in fresh water and mature in salt. If this is getting too specific for some of you, you can lump both types of together under the term diadromous, which refers to fish species that spend some portion of their life cycle in fresh water and other portions in salt.
Regardless of which direction they swim, diadromous species face significant challenges in American Rivers as well as in deep water. Pollution, predation, changing climate conditions and excessive harvesting have all taken their toll, but the physical impediments to fish migration in our rivers are perhaps the most dramatic reason for their steep decline. New England in particular has a massive number of impounded rivers and streams, with nearly 1,200 dams in Massachusetts alone. The USFWS map at left is animated at this link to show the progression of dam building over time in a rather dramatic fashion. While vital during some stages of this region's industrial past, and still used for electrical generation in places along many of our major rivers, many of these dams no longer serve these purposes and their removal to facilitate fish passage is a cornerstone of many freshwater conservation proposals in our region. Species like Atlantic Salmon are virtually absent now and other once plentiful species like blueback herring my become non-viable here without better access to inland spawning areas currently denied to them by dams.
Dam removal is a very difficult and costly undertaking, which is why so many dams remain in place. There are those who value the flatwater behind the impoundments for scenic and recreational purposes who oppose removal on those grounds. There there is the question of permitting, and sediments behind the dams that may be contaminated with all manner of toxins and pollutants. In the Housatonic River, the issue of PCBs is directly linked to the issue of dam removal, and so, too is hydropower, with five dams in Connecticut that generate electricity for the region.
Fish ladders and other forms of upstream assistance are sometimes viable alternatives to dam removal for certain species. The American Eel may get an assist over one of the largest dams on the Housatonic via a temporary eel ladder as part of an effort to restore this species to sections of the river where it occurred historically but has long been absent. The AP reports:
FirstLight Power Resources Company Inc. is working with state and federal agencies to build a temporary eel ladder on the Stevenson Dam on the Monroe/Oxford town line.
Plans call for the company to build similar structures on its other dams, allowing the American eel to make its way up river as far north as Massachusetts.
The plan is part of an effort on the East Coast to restore eel populations, which in recent years have declined so rapidly that the eel has been considered for inclusion on the nation's endangered species list.
'Historically, we know they used to be in the river,' Steven Gephard, supervising fisheries biologist with the state Department of Environmental Protection, said last week. 'They used to catch big ones, as far north as Lakeville. And we know there are none above the dams now.'
Alex Haro, a biologist with the U.S. Geological Survey's Conte Anadromous Fish Research Center in Turners Falls, Mass said bringing eels to the Housatonic is an environmental plus.
'Eels play a significant part in the environment,' Haro said. 'They're generalists, they feed on a great variety of invertebrates. And they're food for just about anything that can eat them — bass, trout pickerel. Herons love them. Cormorants love them. Let's say they go down easily.'
One of the reasons people have been hesitant about installing fish ladders is that they can assist more than just desireable species like eels upstream. Sea Lamprey, which can become a real concern for anglers if they become landlocked, may also find passage via the ladders. One assumes this first ladder is temporary so that its target and non-target impacts can be evaluated. Eels are able to get over natural barriers that block many other species, though I'd imagine the Great Falls of the Housatonic at Falls Village, CT was a hard boundary for upstream movement for just about every fish species, be they anadromous or catadromous or merely instream migrants. It would be great to see the river reconnected to the sea in this fashion, and I look forward to seeing the results of this first leap forward for eels in the Hous.