Title page for ETD etd-0522103-164451


Type of Document Dissertation
Author Switzer, Theodore Scott
Author's Email Address TSSwitzer@aol.com
URN etd-0522103-164451
Title The Ecology of Two Estuarine-Dependent Tonguefishes, the Blackcheek Tonguefish (Symphurus Plagiusa) and the Offshore Tonguefish (S. Civitatium), in Coastal Louisiana
Degree Doctor of Philosophy (Ph.D.)
Department Oceanography and Coastal Sciences
Advisory Committee
Advisor Name Title
Donald M. Baltz Committee Chair
Charles A. Wilson Committee Member
Edward J. Chesney Committee Member
James P. Geaghan Committee Member
Lawrence J. Rouse, Jr. Committee Member
Kenneth M. Brown Dean's Representative
Keywords
  • fish ecology
  • microhabitat
  • Barataria Bay
  • estuary
  • flatfishes
  • Vermilion Bay
  • tonguefishes
  • nursery habitat
Date of Defense 2003-05-16
Availability unrestricted
Abstract
The pattern and process of wetland loss in coastal Louisiana has the potential to influence the distribution and abundance of fishes and macroinvertebrates that utilize inshore estuarine habitat as nurseries during their early life histories. Current management plans designed to stabilize marsh elevations, such as freshwater diversions, may also influence the distribution and abundance of estuarine-dependent nekton. Given the importance of nursery function of inshore estuaries in coastal Louisiana, it is of interest to explore the response of estuarine-dependent organisms to environmental gradients. To this end I examined the ecology of two sympatric tonguefishes, the blackcheek tonguefish (Symphurus plagiusa) and the offshore tonguefish (S. civitatium), in coastal Louisiana. Both species are common transients, occupying estuarine waters from post-settlement to early adulthood. Examination of patterns of resource utilization within the Barataria study area identified significant differences between species with respect to microhabitat selection. Offshore tonguefish were generally more abundant than blackcheek tonguefish in the Barataria study area. Blackcheek tonguefish used lower salinities, higher temperatures, finer substrates, shallower depths, and were found closer to shore than offshore tonguefish. Ontogenetic shifts in resource utilization were also evident for both species; larger individuals typically utilized warmer waters with lower dissolved oxygen concentrations and higher salinities, and were collected farther from shore in deeper water over coarser substrates. Blackcheek tonguefish were abundant along the marsh edge while offshore tonguefish were rare, indicating the apparent avoidance of marsh-edge habitat by offshore tonguefish. In a similar study conducted in the Vermilion system, blackcheek tonguefish were more abundant than offshore tonguefish, indicating that salinity can substantially alter the distribution and abundance of these tonguefishes. Examination of growth rates within the Barataria system indicated that offshore tonguefish grew at a significantly higher rate than did blackcheek tonguefish. Growth of both species was significantly affected by various biotic and abiotic factors. Qualitative loop analyses indicate that tonguefish abundances are potentially affected by the input of nutrients, changes in emergent marsh habitat, and alterations in salinity. Environmental changes associated with wetland loss and associated management alternatives have the potential to affect these sympatric tonguefishes as well as other estuarine-dependent species.
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