DISTRIBUTION AND ABUNDANCE OF FISHES IN RELATION TO BARRIERS: IMPLICATIONS FOR MONITORING STREAM RECOVERY AFTER BARRIER REMOVAL

DISTRIBUTION AND ABUNDANCE OF FISHES IN RELATION TO BARRIERS: IMPLICATIONS FOR MONITORING STREAM

RECOVERY AFTER BARRIER REMOVAL

By Cory Gardner

Thesis Co-Advisors: Stephen M. Coghlan Jr. and Joseph Zydlewski

A Lay Abstract of the Thesis Presented

In Partial Fulfillment of the Requirements for the

Degree of Master of Science

(in Wildlife Ecology)

December 2010

Dams are ubiquitous in coastal Maine, and have altered both stream habitats and the distribution and abundance of fishes. These impacts are caused mainly by a disruption of the hydrology, temperature, and habitat connectivity. Sedgeunkedunk Stream, a tributary to the Penobscot River (Maine, USA) has been the focus of a restoration effort, which includes the removal of two dams. 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 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 anticipation of potential range expansion after the completion of the dam removals.

Over three years prior to dam removal, the fish community showed consistent trends in species richness and abundance, with metrics always highest downstream of the lowest dam , always lowest immediately upstream of that dam , and recovering upstream towards the headwaters. Seasonal and annual patterns across all sites were remarkably consistent regardless of sampling episode. Immediately after dam removal, we saw significant decreases in richness and abundance below the former dam site and a corresponding increase in fish abundance at the upstream site, and for the first time, anadromous Atlantic salmon were found upstream of the former dam site.

In 2008 47 sea lamprey entered the stream; 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.  Sea lamprey frequently ascended to the first dam encountered before swimming back downstream and beginning spawning.  Nests were distributed from head-of-tide to the lowermost dam; no spawners or nests were observed 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.