Date Awarded

2006

Document Type

Dissertation -- Access Restricted On-Campus Only

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Deborah A. Bronk

Committee Member

John E. Olney

Abstract

The objective of this study was to identify important river and estuary habitats of young American shad by estimating their value to fish production. American shad populations across the Atlantic coast have been in decline since the 1800s due, in part, to restricted access to habitat and habitat loss. The study demonstrates that production and year-class strength of Mattaponi River American shad are influenced by allochthonous subsidies from riparian and terrestrial ecosystems, thus habitat quality is related to the watershed's health, and that Chesapeake Bay is an important overwintering habitat for juveniles. Specifically, I characterized production dynamics and biogeochemical processes in the Mattaponi River, a tributary of the York River and the most productive American shad nursery in Virginia's portion of Chesapeake Bay; quantified the contribution of autochthonous and allochthonous organic matter (OM) to zooplankton, macroinvertebrates, and young American shad in the Mattaponi River; identified the trophic pathways that support American shad production within river and estuary habitats during ontogeny; and determined the main habitats within the York River system, from the larval stage to their ocean migration. Mattaponi River production dynamics were strongly influenced by river discharge; during periods of high discharge, primary production was suppressed and greater than 60% of zooplankton, macroinvertebrates and larval American shad production was supported by allochthonous OM. Further, OM concentration, plankton density, and juvenile American shad indices were elevated, demonstrating that allochthonous OM subsidizes the metazoan food web and fish production. Spatial segregation of juveniles rearing in the freshwater nursery zone was identified through a novel application of a stable isotope turnover model; juveniles were shown to reside in habitats of 5-10 river km for a month or longer. These fish emigrate from the nursery zone in November and December, residing and feeding in the York River estuary and Chesapeake Bay before migrating to the ocean in February through April. Variable emigration strategies were observed; most American shad likely emigrated at 2-5 g and spent weeks to months in the estuary, however a few emigrated at habitat.

DOI

https://dx.doi.org/doi:10.25773/v5-t822-xv36

Rights

© The Author

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