Benton’s town leaders were concerned that their upcoming alewife festival might lack one essential ingredient: alewives.

Last year, millions of the foot-long silver fish began showing up in the Sebasticook River in numbers on April 29. This year, when they hadn’t yet shown up by May 7, organizers of the annual festival said they were worried, not least because they had sold more than 50 tickets to a May 16 alewife dinner that kicks off the festivities. Organizers rely on the presence of the fish in order to hand out free smoked alewives during the May 17 festival.

Benton Selectman Antoine Morin breathed a sigh of relief later this week when the first few members of the migration finally began arriving in local waters.

“Mother Nature is a tricky thing,” Morin said, “and I know better than to go against her wisdom.”

The late arrival of the fish, which are heavily harvested primarily for use as lobster bait, but can also be eaten, is likely because of colder water temperatures caused by the unusually harsh winter and cool spring, according to Craig King, who oversees alewife populations for the state Department of Marine Resources.

King said it’s the latest local run of alewives in at least eight years.

Now that the alewife run has begun, King said it will accelerate quickly. At Webber Pond on Seven Mile Stream in Vassalboro, he said he counted four fish on Tuesday, 1,000 on Wednesday and more than 3,000 fish by mid-afternoon on Friday.

LONG JOURNEY

The fish travel from the sea up waterways in a huge plug, trying to stick together to maximize their chances of survival while running a gauntlet of hungry predators.

Observers say local wildlife is becoming increasingly attracted to the rich stream of protein flowing upriver. Kingfishers, eagles, ospreys, herons, minks, snapping turtles and otter can all be seen feasting on the fish during the run.

“For the environment, it’s a huge win,” said Jeffrey Pierce, president of the Alewife Harvesters of Maine.

However, Pierce said the prevalence of predators raises new questions about wildlife management.

In 2011, a pair of seals followed the fish all the way up to Benton, from the Kennebec River into the Sebasticook. It’s unusual for seals to come so far upstream, but Pierce said growing populations have been congregating around the mouths of Maine’s largest rivers to take advantage of the bounty, which includes salmon and eels along with alewives.

“This year, there are 400, 500 seals there off Popham Beach,” he said. “They’re literally driving the alewives up onto the beaches. I’ve never seen that before.”

In addition to threatening the alewives themselves, he said, the seals also make it more difficult for haddock and cod, two valuable commodities that also eat the alewives, from returning to Maine’s coast.

Seals may be cute and popular, he said, but they’re “eating machines” and need a check in their population, which he said is hurting fish stocks. He suggests a small limited seal hunt to cull their numbers and prevent them from eating so many alewives.

Pierce said the alewife run may be starting late, but the number of fish he sees downstream indicate that there is a large, healthy population of alewives this year. He said that the delayed run is no cause for alarm and that historical data shows late runs happen from time to time.

Whether all the fish will make the journey up to Benton is debatable. If the water suddenly gets significantly warmer, some of the fish will give up and head back downstream, although no one knows exactly what temperatures will trigger that reaction in how many fish.

“No one can really tell in advance whether it’s going to mean less fish or not,” King said.

Speculating on the number of fish that will arrive in any given year has become a more popular pastime in Benton over the last several years.

FREED RIVERS

The Edwards Dam on the Kennebec River in Augusta, built in 1837, halted the run of the alewives and other migratory fish, such as Atlantic salmon and American shad into Benton and other communities along the Sebasticook River, which feeds into the Kennebec.

In 1999, the Edwards Dam was removed after lobbying by environmental groups. In 2008, the Fort Halifax Dam in Winslow was also removed. That cleared the way for Benton to assert its historical harvesting rights of alewife, first established in the early 1800s.

A state-approved town ordinance makes it legal for Benton to harvest the fish once 225,000 have made it over the Benton Falls Dam, which is equipped with a $1 million fish elevator that passes the fish upstream to their native spawning grounds. The town typically harvests anywhere from 350,000 to 500,000 fish per year.

Alewive harvesting is regulated by the state, both mass harvesting by communities and individual fishermen, who can take up to 25 per day.

There is enough habitat to support a population of 5 million fish, according to Nate Gray, a biologist with the Department of Marine Resources who monitors the fish in Benton.

But the actual number that arrive each year has never approached five million, instead fluctuating with a variety of complex environmental factors that are impossible to predict or control.

In 2009, the total run was about 1.6 million fish. In 2010, it was about 2 million.

When the 2011 run was a staggering 2.7 million fish, it seemed like a sign of even greater things to come, but 2012 had a comparatively bad run, 1.75 million fish. Last year, it increased again, to 2.3 million.

This year, it’s anyone’s guess.

During the peak of the spawning period, as many as 200,000 fish make it over the dam in a single day during the run, which lasts about six weeks.

The answer to how many fish will spawn this year begins in 2010. Because the alewives spawn after four years at sea, this year’s crop hatched from billions of eggs laid in 2010 in a series of ponds and lakes in the upper waters of the Sebasticook River.

The number of eggs laid depends on the number of mature females that spawned that year, with each one capable of laying about 150,000 eggs.

Between then and now, natural predators and weather conditions have whittled down the population considerably, killing off about 99 percent of the alewives before they get a chance to spawn themselves.

An unusually cold rainfall in an upstream lake could drop the temperature a little too low, killing billions of eggs.

Others die of disease or wind up in the gullets of seals and other predators, including humans.

Over the four-year period, the net result of all of those additions and subtractions to the population dictates how many fish will be available for Benton to harvest. The town has traditionally made between $15,000 and $20,000 per year for its share of the harvest; that number could increase if the overall population of fish continues to grow and take advantage of expanded habitat.

There may be a year in which the alewives don’t make it to the Benton festival, but this year at least the fish have come in time to be smoked, fried and turned into chowder for attendees of Benton’s dinner. Morin said festival tickets are still available at the Benton town office.

“Now that they’re here,” he said, “I feel better.”

Matt Hongoltz-Hetling — 861-9287 | [email protected] | Twitter: @hh_matt