DENNYSVILLE – Upon first glance, the dark patches in the small river that bisects this small Washington County town appear to be shadows cast by trees or pools too deep for even the midday sun to penetrate.

But then the shadow moves and, if the sun hits just right, the dark mass begins to glitter. Suddenly it becomes clear that the sandy river bottom is actually hidden beneath several thousand fish swimming in synchronicity.

Untold hundreds of thousands of alewives leave their saltwater habitat between mid-May and mid-June to swim up many of Maine’s coastal rivers to spawn.

The annual return of the alewives to the Dennys River, like river herring runs on many other Maine waterways, has been closely watched by generations of local residents. But this year for the first time, the Maine Department of Marine Resources is seeking to document the size of the run.

Over the course of the past several weeks, the biologists have counted more than 58,000 alewives swimming up the Dennys toward the ponds and lakes where they will spawn.

Data collected by DMR scientists on the Dennys and other rivers will then be used to shape policy decisions on a fish species that serves an important role in both the ecology of Maine’s waterways and the state’s economy.

“The alewife is a very, very important resource … and ties the ocean to our rivers and our lakes,” Colby Bruchs, a DMR fisheries biologist, said last week while standing atop a temporary fish weir in Dennysville. “If we can assess the population over time, we can make better management decisions.”

Unlike the beloved Atlantic salmon that once crowded New England rivers, alewives are not particularly attractive as either a sport fish or a highlight on a dinner plate.

Spawning adults typically are 10 to 14 inches long and weigh between one-half and 1 pound, but they are skinny and bony, with oily flesh. The term “river herring” actually refers to both anadromous or sea-run alewives and a similar-looking fish, the blue-backed herring.

DMR has operated a fish weir on the Dennys since 1999 in order to count and release returning sea-run Atlantic salmon. Just three salmon had returned this spring as of Friday.

Biologists also use the weir to prevent escapees of local salmon aquaculture facilities from spawning with wild fish.

But this year crews installed lobster cage wire over the grates to also prevent sea-run alewives, which are much smaller than an adult Atlantic salmon, from passing through the weir gates.

The fish corral themselves into a trap or two pens and are then hand-netted for counting purposes before being allowed to continue their migration.

Bruchs said he and the other DMR staff members working the weir have had to assure concerned and sometimes angry local residents or passers-by that they were, indeed, allowing all of the fish to continue upstream.

River herring, particularly the hatchlings, are an important forage fish for other species in the river and ocean. But in an example of nature’s intricate web of life, the alewife spawning runs often coincide perfectly with the out-migration of juvenile Atlantic salmon to the ocean.

Atlantic salmon populations in the Dennys and seven other Maine rivers are federally protected endangered species.

“So you have thousands of alewives covering up the salmon and it really saves them from being preyed upon by ospreys and eagles” and other predators, Bruchs said. “If they see thousands and thousands of fish like this at the top of the water, they are much more likely to grab an alewife than one of our salmon.”

River herring populations appear to be cyclical, although average runs today are much smaller than in decades past. While numbers fluctuate wildly from river to river, the 2008 spawning run has been strong, according to preliminary figures.

“It’s been a very good year,” said Patrick Keliher, executive director of DMR’s Bureau of Sea-Run Fisheries and Habitat. “Most of the runs midcoast and Down East have been strong. We had a good run on the Kennebec and we couldn’t be more pleased with the Dennys. We didn’t know what to expect.”

River herring have been an important bait fish for some Maine lobstermen for decades. Nearly three dozen towns still have commercial harvesting rights, which are often leased to independent fishermen.

But harvest levels have dropped dramatically as the population declined. More than 3 million pounds of river herring were harvested throughout much of the 1950s, but that figure has dropped to 1 million pounds or less since the mid-1980s.

In recent years, the humble alewife has been at the center of a heated political controversy unique to the St. Croix River.

In 1995, the state of Maine closed the Woodland and Grand Falls dams on the St. Croix to upstream passage of alewives. Registered guides and local residents had pushed for the closure based on concerns that the large runs were decimating the smallmouth bass and landlocked salmon fisheries that make up a pillar of the local economy.

Environmental groups and some biologists on both sides of the Maine-Canada border argued that alewives co-exist with bass, salmon and other sport fish throughout Maine and beyond. They blamed the crash in bass populations in Spednick Lake on other factors.

Political skirmishes flared up periodically until earlier this year when, under a hard-fought compromise, the Legislature voted to reopen the Woodland dam to alewives. State agencies must put together a management plan for river herring before allowing the fish beyond Grand Falls.

Keliher said they are not currently counting alewives that pass the Woodland dam. But Lee Sochasky, executive director of the St. Croix International Waterway Commission, said last week that roughly 12,000 alewives had been counted at the downstream Milltown dam.

Studies done during the 1980s indicated that about 50 percent of the fish that passed through Milltown also went beyond Woodland, Sochasky said. The number of fish returning to Milltown annually has dropped precipitously – from more than 2 million in the late 1980s – since the two dams were closed.

“Allowing them into the Woodland flowage gives them some spawning habitat and gives them an opportunity to start to rebuild those populations,” Sochasky said.

kmiller@bangordailynews.net

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