Date Awarded

2000

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Carl H. Hershner

Committee Member

John E. Olney

Abstract

Delineation of essential fish habitat is particularly difficult for migratory fish which utilize large expanses of habitat throughout their life history. This study's main objective was the development and evaluation of habitat assessment tools for the early life stages of American shad (Alosa sapidissima) in two coastal plain rivers. to accomplish this, shad spawning and larval nursery habitats were delineated in the Mattaponi and Pamunkey rivers using presence of eggs and larvae (1997--1999) as evidence of habitat use. A watershed habitat assessment protocol was developed and used to rate habitat based on hydrographic, physical habitat, shoreline and land use parameters. These parameters were evaluated for associations with the presence of shad eggs and larvae to corroborate habitat ratings. Values for parameters used in the ratings were obtained from field assessments, long-term data sets and remote sensing in attempts to combine best-available data. Multivariate statistical analyses indicate the importance of hydrographic parameters (current velocity, dissolved oxygen and depth); physical habitat features (sediment type and deadfall); and forested shoreline/land use features to presence of eggs. Larvae were more dispersed than eggs and distinct habitat associations could not be discerned. Morphological features indicate the presence of three distinct regions along the Mattaponi and Pamunkey river gradients. Presence of eggs is typically associated with upstream and mid-river regions, while larvae were dispersed amongst the three regions. Shad eggs and larvae were more abundant on the Mattaponi River than the Pamunkey River, which is concordant with juvenile abundance. Abiotic factors hypothesized to impact spawning location, larval transport, development rates and predator/prey abundance were also examined. Utilizing the juvenile Alosa index (1991--1999) as an estimate of juvenile shad recruitment, correlation with discharge, precipitation and water temperature (March--June) was examined. Hydrographic conditions during May and June appear to most accurately predict juvenile recruitment patterns in the Mattaponi River, however trends in the Pamunkey River were not as consistent. Ultimately, discharge affects transport of weak-swimming larva to variably favorable nursery habitats. A conceptual hydrodynamic model was developed which explores potential impacts of variable habitat exposures on larvae driven by spawning location, habitat suitability, discharge and hatching rates.

DOI

https://dx.doi.org/doi:10.25773/v5-natx-je24

Rights

© The Author

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