Date of Award

Winter 2019

Project Type

Dissertation

Program or Major

Earth and Environmental Sciences

Degree Name

Doctor of Philosophy

First Advisor

David M Burdick

Second Advisor

William H Howell

Third Advisor

Adrienne I Kovach

Abstract

American eels are frequently captured in saltmarsh habitats yet little is known about eel use of these systems. Coastal systems such as salt marshes are vulnerable to habitat impacts due to high rates of coastal development, including impacts from undersized culverts that result in tidally restricted systems upstream. Given the decline in the American eel population, a need exists for a clearer understanding of the functional difference of hydrologically restricted and unrestricted salt marshes in the support of eels. To address data gaps and inform saltmarsh management to support eels, laboratory and field experiments were employed that assessed the value of saltmarsh habitats to the life history of the American eel. Eels held in the laboratory were subject to a diet switch to determine the rates at which eel mucus, fin, muscle, and liver tissue assimilate the carbon and nitrogen isotope values of the diet (turnover rate) and the level of discrimination in each tissue relative to the diet (trophic discrimination factors). These data were used to inform the interpretation of data collected from hydrologically restricted and unrestricted creeks in three New England estuaries. Isotope data indicated strong evidence of salt marsh primary producers contributing to the basal diet of eels as well as consumption of marsh resident secondary consumers. Eel gut contents also contained abundant saltmarsh secondary consumers, confirming that eels serve as top predators and are residents in salt marshes. Greater eel trophic position measured upstream of reference creeks indicates that tidal restrictions may result in an altered food web in the tidally restricted marsh. Models were developed for predicting muscle and liver δ15N and δ13C from mucus and fin to provide a non-lethal alternative for sampling yellow eels for stable isotope analysis. Trends in data from a telemetry study suggest that eels released upstream of an undersized culvert with a self-regulating tide gate travelled shorter distances than eels in the reference creeks and had delayed movements to downstream areas of the marsh relative to eels in the reference creek. This study addresses a critical data need for the management of salt marshes to support eels. It provides evidence of eel use of salt marshes as important foraging resources, negative impacts of tidal restriction on trophic support and movement of eels, as well as important data to support future stable isotope analysis of eels. The cumulative impact of marsh loss and degradation, such as through tidal restriction, may be a contributing factor in the decline of eel populations. Conservation and restoration of salt marshes as habitat and management of marshes to maintain ecological integrity will provide critical trophic support and access to essential resources for the American eel population.

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