A three-year study started this year by researchers at the Gulf of Maine Research Institute and the University of Southern Maine’s Aquatic Systems Group hopes to shed light on what until now has been the secret life of the alewife.
Although alewives have been commercially important to Maine communities for generations, little is known about alewife ecology, according to Jason Stockwell, a pelagic ecologist with the Gulf of Maine institute who is overseeing the study.
Researchers hope that by gathering more information about the lives of alewives, they will be able to better understand declines in the alewife population in southern New England. That information could help alewife harvesters determine the sustainability of the Maine alewife fishery.
“The alewife population in Maine has remained relatively healthy compared to Massachusetts and areas south,” Stockwell said Monday from the nonprofit marine science center in Portland. “So Maine is a good area to study the fish.”
During the annual alewife run this spring, researchers collected samples from more than 20 rivers in Maine from the Saco to the Dennys River.
“We tried to get 100 fish from each station; in some areas we were able to do that twice,” Stockwell said. “In some of the areas, there’s harvesting going on, and the harvesters were really helpful.”
The study is funded through a grant from the National Fish and Wildlife Foundation with additional funding from Acadia National Park and the National Oceanic and Atmospheric Administration. In addition to local harvesters, the gulf institute and USM had assistance during the collection phase of the study from the Maine Department of Marine Resources, the Somes Sound Wildlife Refuge, Acadia National Park, College of the Atlantic and NOAA.
Alewives are used commercially as lobster bait. They also provide an important food source for osprey, herons, otters, cod, haddock and other animals.
Like salmon, alewives spawn in freshwater environments and migrate to the ocean, but according to Stockwell, little is known about them and where they go when they leave the lakes and rivers where they spawn.
The study hopes to determine whether alewives from one river are genetically different from fish in other rivers and whether they return to the same freshwater areas where they were born, Stockwell said. Researchers also hope to determine whether the fish from different rivers remain as an isolated group when they migrate to the ocean or whether they mix with alewives from other river systems.
By answering these questions, as the study hopes to do, researchers may be better able to determine the effects on the alewife population and explain its decline in certain regions.
Although they know that the Atlantic population of alewives has declined overall, Stockwell said, they don’t know why.
“Some people blame dams, water, the bycatch from trawlers and predation from the striped bass, which has increased since the 1980s,” he said.
The big question focuses on the effects of bycatch in the ocean environment, he said. If specific runs of alewives remain isolated from others in the ocean, a large bycatch event could have a heavy impact on that run, Stockwell said. If runs from different rivers mix together, the impact would be spread across multiple populations, he said.
If they can determine that alewives from specific freshwater systems can be distinguished from one another, researchers and fisheries managers may be able to better monitor populations from different runs, evaluate the impact of the unintended capture on specific alewife populations and unlock the mystery of where alewives go once they leave Maine rivers.
With the collection process completed, the researchers have begun working on the fish they collected. Stockwell said they will use three methods to study the fish over the next two years.
“When you combine these methods, we can develop a good classification system to identify where the fish come from,” Stockwell said.
Researchers will use genetic testing, physical measurements to determine whether there are physical differences among fish from different rivers, and a study of the alewives’ ear bones.
The ear bones — or otoliths — grow steadily as the fish ages, and, like trees, they grow in layered rings that can be counted to tell the age of the fish.
Younger fish also grow daily growth rings, particularly in their first year, Stockwell said. By examining those daily growth rings, scientists can determine how fast the fish was growing during that first year.
That information also may help researchers pinpoint which Maine rivers and lakes the alewives came from. An alewife that grew in a warmer environment, such as the Kennebec River system, would have wider rings, while a fish that grew in the East Machias system, where the water is colder and the growing season is shorter, would have narrower rings, he said.
Data from the physical examination of the fish samples should be available by the end of the summer, he said. That information will be shared with harvesters along the coast and could help them to document that their fisheries are sustainable. The Atlantic States Marine Fisheries Commission has adopted a new policy that requires fisheries in each state to provide that proof by 2012, Stockwell said.
Massachusetts, Connecticut, Rhode Island, North Carolina and Virginia already have closed their alewife fisheries. Under the new regulations, Maine fisheries also could be forced to close unless they are proved to be sustainable.
The genetic material from the Maine alewife samples will be studied at an outside laboratory. Researchers at the Gulf of Maine Research Institute will study the otoliths. The results of the entire study should be available by the spring of 2012, he said.