A removal of the Orland Village
dam would have numerous ecological benefits for species and habitats of
interest to NOAA Fisheries. Historically, before the presence of a dam at the
site, tidal flow extended at least two miles farther upstream into the Narramissic
River, creating a complex mosaic of tidal reversing falls and salt marshes teeming
with fish species that are still found in the lower Penobscot River today,
including alewife and blueback herring, Atlantic salmon, American eel, rainbow
smelt, striped bass and possibly shortnose sturgeon.
Benefits of a dam removal for
some species, such as rainbow smelt, could be profound. In the spring, adult
smelt migrate upstream from saltwater to freshwater riffles above the head of
tide for spawning. Rainbow smelt are relatively poor swimmers and are not able
to ascend steep, narrow fish ladders such as exist at the Orland Village dam.
Without a dam, rainbow smelt would likely move upstream to spawning areas below
Alamoosook Lake. Obviously, successful reproduction is critical for fish like
rainbow smelt to sustain their populations. Rainbow smelt, being relatively
small, are fairly low on the food chain and therefore provide nutritious forage
for lots of fish and wildlife.
While the existing fish
ladders do pass some species, notably alewife, the passage is thought to be
severely compromised. At lower tide levels, the fish ladders are completely out
of the water, leaving them inaccessible to upstream migrating fish.
At higher tide levels, fish may
be delayed as they search for the narrow entrances to the fish ladders, or
experience trauma as they try to crowd into passages that are considered too
small for the potential size of the alewife run on the Orland River, which
could be over one million adult alewives attempting to migrate to upstream
spawning habitat. The compromised passage means that fewer fish can move
upstream, which means fewer fish spawning and fewer alewives migrating back to
the Gulf of Maine. For a species like alewife, improved passage through dam
removal would likely have the beneficial effect of boosting the run size,
resulting in more fish in the Orland River, lower Penobscot River and the Gulf
of Maine.
Alewives are also thought to
be impacted by the lack of dedicated downstream passage at the Orland Village
dam. After spawning in upstream lakes, many adult alewives will try to migrate
back to the Gulf of Maine, returning to the Orland River in subsequent years to
spawn again. Successful downstream passage for adults requires deep channels
for outmigration that don’t exist at the Orland Village Dam. Outmigrating
juvenile alewives also experience well-documented problems with downstream
passage, when the dam acts as a strainer and results in large kills of fish on
the timber spillway.
If able to migrate
successfully, juvenile alewives would migrate back to Penobscot Bay in
abundance and provide forage for groundfish such as cod, haddock and pollock.
Similar to the improvements in upstream passage, removal of the Orland Village
dam would improve downstream passage for alewives and increase the distribution
and numbers of prey fish in the Gulf of Maine.
The restoration of historic
salt marsh habitat upstream of the Orland Village dam is likely to have
beneficial ecological impacts as well. Currently the impoundment upstream of
the dam is relatively shallow, warm and poorly oxygenated in some areas, an
artificial habitat that is favored by non-native species such as smallmouth
bass and chain pickerel. A dam removal would restore brackish tidal flow to
nearly two miles of river, with large freshwater marshes reverting to salt
marshes that would teem with small forage fish such as mummichog. With small
fish come bigger fish, such as striped bass, and marine mammals, such as harbor
seals, that might swim in and out with the tide in a reconnected Orland River.
