Author

Cory Gardner

Date of Award

12-2010

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Stephen M. Coghlan Jr.

Second Committee Member

Joseph Zydlewski

Third Committee Member

Kevin Simon

Abstract

Dams are ubiquitous in coastal Maine, and have altered both instream habitats and the distribution and abundance of fishes in these habitats. These impacts are caused mainly by a disruption of the natural hydrology, temperature regime, and habitat connectivity due to physical barriers; the subsequent fragmentation limits the movement of resident fishes, and prevents anadromous fishes from reaching historic spawning habitat. Dam removal has become a common method for restoring streams to a more natural state, but often the response of the fish community is not monitored rigorously. Sedgeunkedunk Stream, a small tributary to the Penobscot River (Maine, USA) has been the focus of a restoration effort, which includes the removal of two dams (at 0.6 and 5.3 km upstream of the Penobscot confluence). Currently sea lamprey (Petromyzon marinus) is the only anadromous species known to spawn successfully in the system. In this study we quantified fish community metrics, by conducting electrofishing surveys, along a headwaters-to-mouth gradient in Sedgeunkedunk Stream, establishing pre-removal baseline conditions and variability. We also described the distribution and abundance of spawning of sea lamprey in Sedgeunkedunk Stream, in anticipation of potential range expansion after the completion of the dam removals. Sea lampreys, and their nests, were censused using daily stream surveys and a mark-recapture model. Over three years prior to dam removal (2007-2009), the fish community in Sedgeunkedunk Stream showed consistent trends in species richness and abundance, with metrics always highest downstream of the lowest dam (minima of 14 species and 2.7 fish/m2), always lowest immediately upstream of that dam (minima of 5 species and 0.9 fish/m2), and generally recovering upstream towards the headwaters. Although seasonal and annual variation in metrics within each site were substantial, patterns across all sites were remarkably consistent regardless of sampling episode. Immediately after dam removal, we saw significant decreases in richness and abundance (10 species, 0.7 fish/m2) below the former dam site and a corresponding increase in fish abundance at the upstream site (5 species, 5.0 fish/m2), and for the first time, anadromous Atlantic salmon were found upstream of the former dam site. No such changes were obvious in a reference stream. In 2008 forty-seven sea lamprey entered the stream, and constructed 31 nests; all fish received PIT tags, which allowed us to identify and follow movements of individuals. Individuals that arrived early in the run were active in the system longer, and used more nests, than did late migrants. Sea lamprey frequently ascended to the first dam encountered before swimming back downstream and beginning nest construction. Nests were distributed from head-of-tide to the lowermost dam; no spawners or nests were observed in the tidally-influenced zone or upstream of this dam. Our results show that by quantifying baseline conditions in a small stream before restoration, the effects of stream restoration efforts on fish communities can be monitored successfully. Based on the observed movements in the system, and the range of their habitat use, we anticipate that spawning sea lamprey will re-colonize formerly inaccessible habitat

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