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The role of the Cape Fear River discharge plume in fisheries production : aggregation and trophic enhancement

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
W. Coult Markovsky (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Thomas Lankford

Abstract: Estuarine habitats have long been valued as critical nurseries for estuarine dependent species of finfish and shellfish. The role of nearshore coastal habitats, particularly river discharge plumes, in fisheries production is less clear. Past researchers have suggested that discharge plumes may enhance fisheries production by: 1) aggregating larval fishes and crustaceans, and 2) providing them with a trophic advantage compared to adjacent ocean habitats. I tested these hypotheses through sampling in the Cape Fear River discharge plume (CFR), North Carolina. Physicochemical conditions were described for plume and adjacent ocean habitats to compare their relative suitability for ichthyoplankton. Temperature and salinity were significantly different between ocean and plume habitats and between the surface and bottom for 2002. In contrast, temperature was not significantly different between ocean and plume habitats but salinity was for 2003. Monthly ichthyoplankton sampling was conducted at stations inside and outside the CFR plume during 2002 and 2003. Ichthyoplankton were sampled using 60cm plankton nets (705µm mesh) towed at the surface, 1 meter, and bottom depths during daylight hours on ebbing tides to: 1) compare larval concentrations and diversities, and 2) examine vertical distribution. Thirty-three taxa of fishes from twenty-two families were collected in 2002 and eighteen taxa from eleven families were collected in 2003 with a total of 1,497 larval fishes collected. Dominant families for 2002 were Sciaenidae, Blenniidae, and Gobiidae. The dominant families differed slightly for 2003 and were Engraulidae, Gobiidae, and Sciaenidae. Seasonal transitions in taxonomic composition occurred in the fall and spring of both years. Total ichthyoplankton concentrations and diversities were generally higher inside of the plume than at ocean stations. Within the plume, ichthyoplankton concentrations were higher at the bottom than at surface and 1 meter depths, suggesting that larvae may be utilizing selective tidal stream transport to facilitate estuarine ingress. Larval diversities for the ocean habitat were highest at the depth of 1 meter. Biochemical assays (cytochrome c oxidase and hexokinase activities) and otolith microstructural analysis were used as condition indices to examine Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus) and brown shrimp (Farfantepenaeus aztecus) collected from plume versus estuarine habitats. No significant differences in enzyme activities or recent growth rates were observed, suggesting that the plume habitat may promote levels of physiological condition comparable to those of estuarine habitats. Future studies to examine the function of river discharge plumes in fisheries production should focus on habitat suitability and compare physiological condition of fishes and crustaceans in these habitats to surrounding waters. Improved understanding of the influence of discharge plumes is needed to determine whether these areas may be designated as Essential Fish Habitat.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Fish populations--Effect of pollution on, Estuarine ecology--North Carolina--Cape Fear River, Fish populations--North Carolina--Cape Fear River
Subjects
Estuarine ecology -- North Carolina -- Cape Fear River
Fish populations -- North Carolina -- Cape Fear River
Fish populations -- Effect of pollution on