By Gerry Boyle

CLA Director

So what effect did last summer’s drought have on China Lake’s alewife population?

Not much, and certainly not a negative one.

That’s according to Nate Gray, marine resource scientist for the state Department of Marine Resources, who has been involved in the historic reintroduction of the anadromous fish to China Lake since the plan’s inception.

The drought, with its resulting low water, followed heavy rainfall in June that increased outflow from the lake into Outlet Stream and down the fish passage in North Vassalboro. “And that was that,” Gray said. “It never rained again.”

But before the water level fell due to lack of inflow and evaporation, 2.7 million alewives, down an estimated 500,000 from the previous year. Why? Gray explained that while alewives’ homing instinct is strong, so-called straying rates (when migrating alewives go a bit off course) can be affected by stream flow, whether adults hug one side of a river or another, or follow a larger school and miss their turn. In this case, that may result in some fish continuing up the Sebasticook River to Benton Falls.

In any event, the nearly 3 million alewives swam up the fishway in North Vassalboro, and on into China Lake. The run is long enough in duration (peak was about May 24) for adult alewives to be exiting the lake after spawning at the same time other adults are making their way in, Gray said.

In June, “I’m balancing the out-migrants, both adults and juveniles,” he said, noting that it takes about a

month for the larval alewives to grow into something that looks like a tiny fish. “Those are still coming

out at this moment,” Gray said in early November.

The annual fall drawdown was then underway, and at some point water flow would decrease to a trickle.

But what happens if juvenile alewives can’t exit the lake and head for salt water before winter?

“Nothing,” Gray said. “They just stay. They’ll hang around and work the resources as long as they can.” That species of fish, the alewives, are planktivores. “You get them out, you do have a net export of phosphorous,” he said.

And the cycle continues, with adult alewives using their homing instinct to return to their home lakes, and

juvenile alewives living in the ocean for several years (the fish reach sexual maturity in four years) before

making their way up rivers and streams to spawn in lakes like China.

And those fish are among the very few that complete the cycle, Gray said. A female alewife can produce

100,000 eggs or more. Only a few eggs grow to the juvenile stage, and of those, only a couple grow to

adulthood. “That’s what you’re left with,” Gray said. “One in fifty thousand.”

And the drought? Would that reduce the number next year? Water quality was better, which could lead to a better survival rate for juvenile alewives. And the lake’s

latent phosphorous is more than enough to feel overwintering fish, Gray said. “The drought,” he said,

“shouldn’t have any detrimental effect on next year.”

Photo credit: TownLine