Date of Award

12-2012

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Stephen Coghlan

Second Committee Member

Joseph Zydlewski

Third Committee Member

Kevin Simon

Abstract

Sedgeunkedunk Stream, a 3rd-order tributary to the Penobscot River, Maine historically supported several anadromous fishes including Atlantic salmon Salmo salar, alewife Alosa pseudoharengus, and sea lamprey Petromyzon marinus. However, 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 with removal of the lowermost Mill Dam thus providing access to an additional 4.7 km of lotic habitat and unimpeded passage into the lentic habitat of Fields Pond. In anticipation of these barrier removals, we monitored stream fish assemblages in strategically-placed impact and reference sites with backpack electrofishing surveys twice yearly since 2007. Results as of August 2011 indicated that density, biomass and diversity of the resident fish assemblage increased at all impact sites upstream of the 2009 dam removal, and no distinct changes in these metrics occurred at unaffected reference sites. Additionally, we documented recolonization and successful reproduction of three anadromous species in previously inaccessible upstream reaches. Three age classes of juvenile Atlantic salmon including emergent young-of-the-year fry were observed approximately 2-km upstream of the former Mill Dam in 2011. Adult alewives were intercepted at upstream impact sites en route to previously inaccessible habitat in Fields Pond, and their progeny were observed exiting the system en route to the Atlantic Ocean during our late-summer sampling in 2011. Finally, sea lamprey larvae were encountered in previously inaccessible upstream reaches during electrofish surveys in 2011. Sea lampreys reliably utilized accessible downstream habitat prior to the 2009 dam removal, and were therefore chosen as a focal species to quantify recolonization. During spawning runs of 2008 through 2011 (pre- and post-dam removal), individuals were marked with PIT tags and their activity was tracked with daily recapture surveys. Open-population mark-recapture models indicated a four-fold increase in the annual abundance of spawning-phase sea lampreys with estimates rising from 59 ± 4 (N ± SE) pre-dam removal (2008) to 223 ± 18 and 242 ± 16 post-dam removal (2010 and 2011 respectively). Accompanying the marked increase in annual abundance, we observed a nearly three-fold increase in nesting sites rising from 31 nests pre-dam removal (2008) to 128 and 131 nests post-dam-removal (2010 and 2011 respectively). The rigorous cataloguing of sea lamprey nests afforded us the opportunity to return to exact nesting locations to address the hypothesis that sea lampreys act as ecosystem engineers in freshwater spawning streams. Sea lamprey spawners use their suctorial disc mouths to rearrange gravel and cobble substrates during nest construction, and these physical modifications to the stream-bed may have immediate and persisting effects upon the stream-dwelling community. Metrics including fine sediment coverage, proportion of embedded particles, stream-bed depth and current velocity, and benthic invertebrate density and diversity were measured in the mounds, pits and adjacent reference locations at randomly selected nesting sites. Analysis of these metrics revealed that sea lamprey spawning activities conditioned stream-bed topography favorably for benthic invertebrates and possibly drift- feeding fishes. Fine sediment coverage and proportion of embedded particles were significantly reduced in mounds relative to pit and reference microhabitats, and sea lamprey nest constructions increased stream-bed complexity by producing shallower mounds with increased velocities adjacent to deeper pits with lower velocities. During autumn sampling we found that almost all of the sea lamprey induced changes to the stream-bed persisted for a period of nearly four months following the cessation of spawning. In summary, these results clearly demonstrate that dam removal has enhanced the density and diversity of the resident fish assemblage by providing an undisrupted stream gradient linking diverse habitat sources including a small headwaters lake, a small headwaters tributary, a large coastal river and estuary, and the Atlantic Ocean. Dam removal has also facilitated the recolonization of previously inaccessible habitat by three anadromous fishes including Federally Endangered Atlantic salmon. Finally, the freshwater spawning activities of anadromous sea lampreys improved physical conditions at the microhabitat level for benthic invertebrates and possibly drift-feeding fishes.

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