Old Lyme — An Earth Day lecture at Lyme-Old Lyme High School Tuesday drew attention to migration patterns and the vital role two fish species play in the local environment.

The first speaker, Steve Gephard of the Inland Fisheries Division of the state Department of Energy and Environmental Protection, spoke about the challenges facing the alewife, a fish species that migrates between freshwater and saltwater during its various stages of development.

Since the country began industrializing, more and more dams have been built, halting the alewives' fishways. About 4,000 dams span the small state of Connecticut, he said.

The alewife population is declining up and down the East Coast because of various challenges: The fish may be blocked off by dams or become the bycatch in Atlantic herring fisheries, for example. Gephard said the fish are needed in abundance, especially as a food source for many local species.

"By building fishways or removing dams we can reconnect them with their natural habitat," he said, stressing the important role local communities play in alewife preservation.

He highlighted local fishways, including one at Ed Bills Pond in Lyme and another at Bride Brook in East Lyme, where a fish counter collects data on the alewives or even transports the healthy fish to other waterways that are in need of more alewives. He also lauded a recently completed fish ladder in Old Lyme, part of the Rogers Lake dam replacement project. He pointed to data that showed the lake's acreage could ultimately support more than 700,000 fish.

"This could become one of the largest alewife runs in the state of Connecticut," Gephard said, adding that it could take decades for that to occur, but the fish amount could build each year.

The second speaker was Paul Spitzer, a conservation biologist who graduated from Lyme-Old Lyme High School 50 years ago and was a protégé of famed ornithologist Roger Tory Peterson. Previously, Spitzer had helped research the effects of the now-banned pesticide DDT on ospreys and their eggs on Great Island in Old Lyme. DDT was shown to make ospreys' egg shells thin and fragile.

Spitzer is now turning his attention again to the osprey on Great Island, but this time to their food chain: focusing on the menhaden, a food source for the osprey. The fish are subject to over-harvesting in the mid-Atlantic, but Long Island Sound functions as a sanctuary for them, he said.

A supporter of "celebratory biology," he said researching the relationship between the fish and the ospreys in the area could yield further details on the menhaden and show the benefits of protecting the local food chain. He also focused on the unique features of the ospreys and their annual migration from the tropics to the local area.

k.drelich@theday.com