Wherever sports folks meet in person or on the Internet, dam removal on Maine's coastal rivers occasionally generates conversations about sea lampreys -- a parasitic fish that looks like a creature from a horror flick.

This lack of aesthetics adds to the image of the species being a bad guy, so misinformation about this creature sometimes astounds astute observers of the natural world.

Each spring, migrating lampreys return from the Atlantic and ascend flowing waters to spawn. This anadromous invertebrate resembles an eel, but in truth, lampreys do not belong to the eel family, the latter a catadromous vertebrate. In fact, lampreys are a first cousin to hagfish, a slimy, ugly critter in its own right.

Lampreys average 2 to 2 1/2 feet long, which equals the length of a human arm, an intimidating size to folks who dislike creepy, slithering critters. Worse yet, lampreys can grow to four feet -- really intimidating -- but I've never seen one that large.

Because of its looks and size, lampreys strike some folks as evil incarnate. The adults prove quite benign, though, and in fact, their fresh-water spawning runs benefit a river system in two ways.

1) Spring spawning occurs when rivers often have strong flows. When lampreys move gravel around to make nests for laying eggs -- more than 230,000 for each female -- this excavation work washes silt downstream, keeping the gravel clean for fall-spawning trout and salmon. In short, lampreys and salmonids enjoy a strong, symbiotic relationship.

2) After spawning, sea lampreys die and the decaying carcasses add nutrients to the water, a hard plus to sell folks on a river when these fish are rotting in shallows. The smell can choke a skunk.

Contrary to popular notions among progressive fishing activists, though, juvenile lampreys create a problem for trout and salmon in certain drainages, a fact that receives little press.

After hatching, juvenile lampreys live in sandy river mud for three to 17 years. Then, they emerge and allegedly head to sea before growing old enough to feed on salmonids and other game fish.

However, exceptions exist. If a drainage with lampreys has a large impoundment, particularly one with deep water, the juveniles stay longer before leaving for sea. These slightly older fish feed on salmon and trout.

Central Maine's Sheepscot drainage offers a perfect example. Sheepscot Pond covers 1,215 acres, stretches north-south a few miles and contains a 150-foot deep hole, enough impoundment to hold juvenile lampreys long enough for them to feed on game fish.

During my youth, before fisheries biologists decided to block lampreys at the Coopers Mills dam, it was common to see lamprey scars on salmonids in Sheepscot Pond and the river just downstream and, in fact, many of us would occasionally catch a fish (landlocked salmon in particular) with a small, dark lamprey attached to it.

Folks have tried to debate this Sheepscot example and say lampreys migrated upriver before European settlers arrived, making this parasite a part of nature's ancient equation.

We do not know if that statement is true, though. A dam at the mouth of Sheepscot Pond created a larger impoundment, so we may never know if lampreys once stayed in this drainage to feed on salmonids before humans changed the habitat. I suspect lampreys did, but the Department of Island Fisheries and Wildlife is unsure.

One point is clear, though. Adult sea lampreys run up coastal rivers, streams and even brooks to spawn, and like most anadromous species worldwide, they do not feed during migration, nature's way of protecting the resource. In short, as ugly as lampreys look, the adults are harmless to fish.

If numerous spawning fish the size of lampreys or say Atlantic salmon or alewives did forage in the limited confines of fresh water during migration runs, they would clean baitfish, game fish and insects out of a drainage and completely destroy nature's balance. It's no exaggeration to say that feeding anadromous fish would turn tidal rivers into biological deserts.

When living in the ocean, lampreys prey on other fish, a parasitic creature that sucks onto the sides of their host and extracts body fluids. Naturally, such a large parasite can kill the host, but fish do survive lamprey attacks, particularly predation from juveniles in fresh-water drainages. We know that for a fact because the procedure leaves a round scar on the host fish, which live often enough to show the tale.

The history of the Sheepscot drainage since World War II includes lamprey spawning runs up at least part of the river. In the 19th century, the dam on the Sheepscot River at Head Tide blocked upstream migration of lampreys (and Atlantic salmon), but that changed in 1952 when the old Atlantic Sea Run Salmon Commission (ASRSC) breached it.

After that, lampreys boiled upriver each spring, ascended the old Works Project Administration's fish-way at the Coopers Mills dam and spawned on the Sheepscot between Route 105 and Sheepscot Pond in Somerville and Palermo.

In 1960, ASRSC replaced the old WPA fish-way with a more efficient Denil fish-way, so lamprey runs escalated. In 1968, ASRSC did a more complete job of breaching the Head Time dam, and that really helped add more lampreys to the Sheepscot's upper reaches.

About 1980, DIF&W blocked lampreys at the Coopers Mills dam. A few do get through to the Somerville-Palermo stretch, but the blockage severely curtailed the run.

I'm a strong proponent of dam removal, but at times, dams (on tidal rivers in particular) do block unwanted species from ascending to upper reaches that often hold blue-ribbon salmonid populations. The decision to allow upstream passage must be made after answering two questions:

1) Have upstream dams with fish-ways created a large enough impoundment to hold juvenile lampreys long enough to threaten game fish?

2) Do juvenile lampreys threaten game fish enough to be a concern?

Proper answers should involve studies tailored to each drainage.

Ken Allen, of Belgrade Lakes, is a writer, editor and photographer.