Fish Community Response to a Small‐Stream Dam Removal in a Maine Coastal River Tributary

Abstract

Sedgeunkedunk Stream, a third‐order tributary to the Penobscot River in Maine, historically has supported several anadromous fishes including Atlantic Salmon Salmo salar, Alewife Alosa pseudoharengus, and Sea Lamprey Petromyzon marinus. Two small dams constructed in the 1800s reduced or eliminated spawning runs entirely. In 2009, efforts to restore marine–freshwater connectivity in the system culminated in removal of the lowermost dam (Mill Dam) providing access to 4.7 km of lotic habitat and unimpeded passage into the lentic habitat of Fields Pond. In anticipation of these barrier removals, we initiated a modified before‐after‐control‐impact study, and monitored stream fish assemblages in fixed treatment and reference sites. Electrofishing surveys were conducted twice yearly since 2007. Results indicated that density, biomass, and diversity of the fish assemblage increased at all treatment sites upstream of the 2009 dam removal. No distinct changes in these metrics occurred at reference sites. We documented recolonization and successful reproduction of Atlantic Salmon, Alewife, and Sea Lamprey in previously inaccessible upstream reaches. These results clearly demonstrate that dam removal has enhanced the fish assemblage by providing an undisrupted stream gradient linking a small headwater lake and tributary with a large coastal river, its estuary, and the Atlantic Ocean.

Dam Removal and Fish Passage Improvement Influence Fish Assemblages in the Penobscot River, Maine

“…; Hogg et al. ) that have shown increasing ordinal similarity in sites where connectivity has been restored. Despite changes evident at the assemblage level, we did not find consistent evidence of changes to the composition of assemblages by guilds (i.e., native and riverine species), which may be explained by the persistence of Smallmouth Bass, a nonnative generalist species.…”

“…; Hogg et al. ). These studies and others have highlighted changes common among many dam removals such as recolonization of diadromous fishes in newly available habitat (Hitt et al.…”

“…; Hogg et al. ), and the incorporation of newly available marine‐derived nutrients and energy in stream food webs (Tonra et al. ).…”

Headwater Streams and Wetlands are Critical for Sustaining Fish, Fisheries, and Ecosystem Services

“…; Hogg et al. ). Similarly, the Yurok and Karuk people of the Klamath region in northern California, who have deep cultural and subsistence ties with Pacific Lamprey L. tridentata , provided important information that improved understanding of lamprey population crashes in the Klamath Basin (Lewis ).…”

“…Traditional ecological knowledge provides an important line of evidence supporting protection and restoration of headwaters. For example, Maine Sea Grant and the National Marine Fisheries Service (NMFS) collaborated to document and disseminate harvesters' knowledge of Alewife, Blueback Herring, and American Eel, all of which are returning to headwater streams following recent dam removals (Hitt et al 2012;Hogg et al 2015). Similarly, the Yurok and Karuk people of the Klamath region in northern California, who have deep cultural and subsistence ties with Pacific Lamprey L. tridentata, provided important information that improved understanding of lamprey population crashes in the Klamath Basin (Lewis 2009).…”