R-10-03 Restoration of anadromous fishes: the effects of dam removal and habitat conditioning in spawning streams

Stephen Coghlan
5755 Nutting Hall, Room 240
University of Maine
Orono, ME 04469

Kevin Simon
School of Biology & Ecology, University of Maine

Joseph Zydlewski
USGS Cooperative Research Unit

Maine’s rivers were once linked to the ocean by spawning migrations of diadromous fishes. These fish brought nutrients and energy from the marine realm hundreds of miles into upland, freshwater food webs. Dams, constructed to power mills and later generate electricity, blocked these fish migrations, resulting in decreased biodiversity and productivity. The Penobscot River Restoration Project opened thousands of kilometers of historic fish habitat, with ecosystem-wide effects. 

Sedgeunkedunk Stream, a tributary of the lower Penobscot River estuary, is the subject of a restoration effort to reconnect the stream and its associated lakes to the sea, in advance of the larger project on the Penobscot. One dam was removed and another bypassed with a rock-ramp fishway and monitoring programs continue for fish and macroinvertebrates. Coghlan’s project focused on the sea lamprey, an anadromous fish whose nest-building activity creates habitat for another anadromous fish, the endangered Atlantic salmon. “In Sedgeunkedunk Stream, we observe a spectacular summer ‘greening’ of the river bottom in late June, coincident with sea lamprey carcass decomposition. We wondered what impact marine nutrients delivered by the lampreys have on in-stream communities,” said Coghlan, who calls sea lamprey a sentinel species that both responds to dam removal and enhances the effects of dam removal on other species.

Coghlan and his team documented dramatic and rapid improvements in fish abundance and diversity following dam removal, including upstream range expansion by Atlantic salmon juveniles, alewife, and sea lamprey. Sea lamprey nesting increased more than four-fold within the restored stream system following dam removal, and the lamprey’s spawning activity increased stream habitat diversity. The spawning activities of sea lamprey improved habitat to the benefit of Atlantic salmon. 

The Sedgeunkedunk Stream study provided an example of the scientific scrutiny and evidence often lacking in other river restoration projects. NOAA Fisheries shared the results with West Coast partners involved in the Elwha River dam removal, and used the results in allocating some $1.5 million in funding for monitoring larger dam removals on the Penobscot River. Salmon biologists with the Maine Department of Marine Resources have incorporated data on habitat metrics to determine the value of habitat conditioning by sea lamprey, and to support dam removals in other small coastal streams. The project also was a model for outreach and engagement of the watershed community, through interactions with neighbors, presentations, and media outreach.

Building on these results, Coghlan is continuing his sea lamprey research, studying the effects of carcasses on in-stream productivity and sea lamprey life cycle ecology.


Gardner, C., S.M. Coghlan Jr., J. Zydlewski, and R. Saunders. 2011. Distribution and abundance of stream fishes in relation to barriers: implications for monitoring stream recovery after barrier removal. River Research and Applications DOI:10.1002/rra.1572.

Hogg, R.S., S.M. Coghlan Jr., J. Zydlewski, and K.S. Simon. 2014. Anadromous sea lampreys are ecosystem engineers in a spawning tributary. Freshwater Biology 59:1294-1307.

Hogg, R., S.M. Coghlan Jr, and J. Zydlewski. 2013. Anadromous sea lampreys recolonize a Maine coastal river tributary after dam removal. Transactions of the American Fisheries Society 142(5):1381-1394.


Two-year project, 2010-2012
Total Sea Grant Funds: $105,224