Date of Award

Spring 5-12-2018

Level of Access

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Joseph Zydlewski

Second Committee Member

Joan Trial

Third Committee Member

Stephen Coghlan

Additional Committee Members

Hamish Greig

Erik Blomberg

Abstract

Anadromous species can boost freshwater productivity through nutrient subsidies. Along the Maine coast of the northeast United States, several alewife populations are recovering after freshwater connectivity is restored. Iteroparity in this part of their range may reduce their role as nutrient subsidies. Stable isotope analysis was used to detect marine-derived nutrient input. Spatial and temporal trends were characterized in the St. Croix as a baseline before alewife recovery, and nutrient-diffusing substrates indicated nutrient co-limitation. A reference watershed was used to compare nutrient dynamics when alewives were present versus absent. Results indicated isotope shifts within particular functional feeding groups, but not in the freshwater community as a whole. In addition, potential alleviation of nutrient limitation during the peak of the alewife run was seen.

A deterministic model was developed to explore the theoretical nitrogen and phosphorus dynamics of Alewife migrations under a range of scenarios. At low escapement levels, the number of recruits produced per spawner was high and juvenile nutrient export dominated. At high escapement levels, fewer recruits were produced per spawner, and so adult nutrient import dominated. These trends persisted regardless of scenario, though the magnitude of endpoints changed. When dams were present, the reduction in upstream passage determined adult abundances. Downstream juvenile rates determined recruitment, as well as nutrient export. The effect of poor passage at sequential dams or an in-river fishery depended on their location in relation to spawning habitat. The St. Croix River, which is located between Maine and New Brunswick, has the majority of spawning habitat upstream. When passage in the lower river was varied, phosphorus difference was insignificant at low passage levels. When varied in the upper river, import dominated at a wide range of upstream passage rates when downstream passage was high. This led to a combined effect of more surviving juveniles per spawner, but a narrower range of passage rates that resulted in phosphorus import. Spawner abundance was higher when a fishery was located upstream than at the estuary, highlighting the need to consider dam and fisheries locations in relation to spawning habitat when estimating population recovery and nutrient dynamics.

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