Barrier Removal in Sedgeunkedunk Stream: Sea Lamprey Recolonization and Resident Fish Community Dynamics

Sedgeunkedunk Stream, a 3^rd-order tributary to the Penobscot River, Maine historically supported several anadromous fish species including sea lamprey and endangered Atlantic salmon.  Several small dams constructed in the late 1800s reduced or eliminated spawning runs entirely.  During the spring of 2008, 48 sea lamprey were identified spawning in the lower portion of Sedgeunkedunk Stream accessible to anadromous fishes.  In 2009, efforts to restore marine–freshwater connectivity in this system culminated with removal of the lowermost dam, which opened up 5-km of historic lotic habitat.  Results from a mark-recapture study conducted during the spring of 2010 indicated a spawning population of 140 ± 9 (95% CI) sea lamprey that expanded their range throughout most of the newly accessible habitat.  146 sea lamprey nests were identified throughout the system with 78 occurring upstream of the former dam site.  Additionally, in anticipation of barrier removals, we have monitored stream fish assemblages in strategically-placed sites with backpack electrofishing surveys twice yearly since 2007.  Results indicate that the density of the resident fish community has increased at all sites upstream of the 2009 dam removal with relatively little change at nearby reference sites.  Furthermore, Atlantic salmon parr ranging from 110 mm to 186 mm TL have been encountered consistently at upstream sites where they were absent prior to dam removal.  Clearly, barrier removal has facilitated a successful sea lamprey recolonization event, while providing access to historic habitat for juvenile freshwater life history stages of endangered Atlantic salmon and the resident fish community.