MOUNT DESERT — Attempts to restore the once-abundant spawning runs of alewives here and in Tremont could be threatened by illegal fishing for the species, which is used as lobster bait.

During the past several years, conservation groups, Acadia National Park biologists and the towns of Mount Desert and Tremont have been working to encourage the annual spawning runs. Along with rebuilding fish ladders to help the fish get by dams and other obstacles, studies are being conducted to see if the efforts are paying off.

In Mount Desert, the work is concentrated on the Long Pond-Somes Pond watershed. In Tremont, restoration efforts are focused on Seal Cove Pond.

David Lamon, executive director of the Somes-Meynell Wildlife Sanctuary in Mount Desert, was instrumental in efforts to restore the runs on the Long Pond-Somes Pond watershed. He and others began to look at the issue about eight years ago.

Why numbers have leveled off is a mystery, Mr. Lamon said. One concern, he said, is that he learned at the end of the runs last year that fish were being taken illegally, most likely because of the high price of lobster bait.

The price of lobster bait has been skyrocketing during the past few years. Patrice McCarron of the Maine Lobstermen’s Association estimates that bait prices have jumped about 30 percent since 2007.

The illegal fishing of alewives also is a concern at Seal Cove Pond, according to Acadia National Park biologist Bruce Connery. Last year, there was evidence of the fish being netted in Seal Cove Brook, he said.

The concern is not just that some fish are being taken; the netting of fish can disrupt the run, with fish being injured or swimming back downstream.

“Turning back a couple of hundred fish can make a huge difference,” Mr. Connery said.

For more maritime news, pick up a copy of the Mount Desert Islander.