Hypoxia Tolerance in Two Juvenile Estuary-Dependent Fishes

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dc.contributor.advisor James A. Rice, Committee Chair en_US
dc.contributor.advisor Peter Rand, Committee Member en_US
dc.contributor.advisor Jason Osborne, Committee Member en_US
dc.contributor.author Shimps, Elizabeth en_US
dc.date.accessioned 2010-04-02T18:11:03Z
dc.date.available 2010-04-02T18:11:03Z
dc.date.issued 2004-01-14 en_US
dc.identifier.other etd-12292003-140734 en_US
dc.identifier.uri http://www.lib.ncsu.edu/resolver/1840.16/2180
dc.description.abstract Hypoxia events, or low dissolved oxygen (DO) conditions, occur frequently in North Carolina estuaries during the summer. These events may have harmful effects on important fish stocks, including spot (Leiostomus xanthurus) and Atlantic menhaden (Brevoortia tyrannus), but their consequences are not well understood. As part of a larger study examining effects of hypoxia on juvenile estuary-dependent fishes, I investigated direct mortality due to hypoxia in juvenile spot and Atlantic menhaden. The objectives of these experiments were to determine how the extent of mortality varies with the severity of hypoxia and the duration of exposure, and to explore how vulnerability to hypoxia changes across species, temperature, and fish size. Atlantic menhaden and spot were tested at two temperatures, 25° and 30°C, and three dissolved oxygen concentrations, 0.6, 0.9, and 1.2 ppm. Survival analyses were performed on the data relating survival rate of each species to dissolved oxygen concentration, duration of exposure, temperature, and fish size. The data were also analyzed using an LC₅₀ approach for comparative purposes, and 12-hour LC₅₀ estimates (concentrations causing 50% mortality) ranged from 0.9-1.1 ppm O₂. Spot and menhaden exposed to 1.2 ppm O₂ showed no mortality in 24 hrs at 25°C, and only 30-40% mortality at 30°C. In contrast, both species experienced 100% mortality in 2-6 hrs at 0.6 ppm O₂. There was a modest effect of size on hypoxia tolerance, with small spot being less tolerant than large spot, while the converse size effect was observed for menhaden. Spot were consistently less tolerant to hypoxia than menhaden and both species were less tolerant to hypoxia at 30°C than at 25°C. Preliminary experiments showed that a 24-hour acclimation to sublethal levels of hypoxia caused significantly reduced mortality upon subsequent exposure to lethal hypoxia concentrations. This study is part of a larger effort integrating lab experiments and field observations in a spatially-explicit, individual-based model to quantify changes in fish survival, growth and distribution in response to water quality changes. Results from this study indicate that while direct mortality due to hypoxia will vary with species, size, and temperature, mortality will likely only be substantial when these species are exposed to oxygen concentrations less than about 1 ppm O2. Given the severity of hypoxia necessary to cause mortality and the ability of fish to behaviorally avoid hypoxia, direct mortality due to hypoxia may not occur on a large scale. Therefore, the greatest impacts due to hypoxia may be indirect, due to density-dependent effects on growth and survival as fish avoid hypoxic areas, or via mechanisms caused by stress imposed by sublethal hypoxic conditions alone or in concert with other stressors. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject spot en_US
dc.subject Atlantic menhaden en_US
dc.subject hypoxia en_US
dc.subject mortality en_US
dc.title Hypoxia Tolerance in Two Juvenile Estuary-Dependent Fishes en_US
dc.degree.name MS en_US
dc.degree.level thesis en_US
dc.degree.discipline Zoology en_US

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