Abstract
AbstractThe Penobscot River Restoration Project (PRRP), to be completed in 2016, involved an extensive plan of dam removal, increases in hydroelectric capacity, and fish passage modifications to increase habitat access for diadromous species. As part of the PRRP, Great Works and Veazie dams were removed, making Milford Dam the first impediment to federally endangered Atlantic Salmon Salmo salar. Upstream habitat access for Atlantic Salmon is dependent upon successful and timely passage at Milford Dam because nearly all suitable spawning habitat is located upstream. In 2014 and 2015, a total of 73 adult salmon were radio‐tagged to track their upstream movements through the Penobscot River to assess potential delays at (1) the dam remnants, (2) the confluence of the Stillwater Branch and the main stem of the Penobscot River below the impassable Orono Dam, and (3) the Milford Dam fish lift (installed in 2014). Movement rates through the dam remnants and the Stillwater confluence were comparable to open river reaches. Passage efficiency of the fish lift was high in both years (95% and 100%). However, fish experienced long delays at Milford Dam, with approximately one‐third of fish taking more than a week to pass in each year, well below the Federal Energy Regulatory Commission passage standard of 95% within 48 h. Telemetry indicates most fish locate the fishway entrance within 5 h of arrival and were observed at the entrance at all hours of the day. These data indicate that overall transit times through the lower river were comparable to reported movement rates prior to changes to the Penobscot River due to the substantial delays seen at Milford Dam. The results of this study show that while adult Atlantic Salmon locate the new fish lift entrance quickly, passage of these fish was significantly delayed under 2014–2015 operations.Received January 27, 2016; accepted April 14, 2016
Highlights
Populations of Atlantic Salmon Salmo salar in combined by the mid-1990s
The Penobscot River was not included in the original listing because it has the largest return of Atlantic Salmon in the United States; after continued declines this run was added to the endangered Gulf of Maine distinct population segment (GOM DPS) in 2009
Movement rates through these sections were similar to other nearby open-river sections and were within the range reported for upstream movements of Atlantic Salmon in other studies in the Penobscot River and elsewhere (Økland et al 2001; Gorsky 2005; Thorstad et al 2005, 2008)
Summary
Populations of Atlantic Salmon Salmo salar in combined by the mid-1990s This led to the listing of the the United States are dramatically below historical levels, Gulf of Maine distinct population segment (GOM DPS), with runs declining to 500 to 2,000 fish in all Maine rivers which included eight rivers in Maine, as federally. The Penobscot River was not included in the original listing because it has the largest return of Atlantic Salmon in the United States; after continued declines this run was added to the endangered GOM DPS in 2009. Multiple factors, including overfishing, habitat loss, dams, and pollution, have contributed to Atlantic Salmon declines (Parrish et al 1998; NRC 2004) Of these factors, dams have been identified as a major threat because they obstruct the downstream migration of juveniles, as well as the upstream and downstream migrations of iteroparous adults (NRC 2004). Upstream passage success for Atlantic Salmon at both dams was annually variable and often poor prior to removal (43– 100% at Veazie Dam, 12–95% at Great Works Dam; Holbrook et al 2009), so the demolition of these two dams was anticipated to be a significant step in improving upstream passage for adult salmon in the system
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