Browsing by Author "Dr. Jeffrey A. Buckel, Committee Member"

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Assessing Nursery Quality for Southern Flounder, Paralichthys lethostigma, through Fish Energy Content and Habitat Abiotic Conditions
(2007-08-01) Ellis, Timothy Alan; Dr. David A. Dickey, Committee Member; Dr. Jeffrey A. Buckel, Committee Member; Dr. John M. Miller, Committee Chair
Estuarine nursery habitats are essential to the sustainability of many of the world's fisheries. Anthropogenic perturbations and watershed activities threaten the quality of these vital ecosystems, and the significance of nursery habitat loss has become so distressing that most fishery management strategies now place high priority on the protection and restoration of "Essential Fish Habitat" (EFH, Magnuson-Stevens Act, NOAA 1996). The inability to accurately evaluate habitat quality and fully understand the factors limiting habitat-specific productivity preclude the success of any management efforts to improve fishery recruitment through the protection and restoration of estuarine nursery habitats. The Albemarle-Pamlico Estuarine System in North Carolina (NC) provides important nursery habitat for many ecologically and economically important species, including southern flounder, Paralichthys lethostigma. Abiotic factors, in particular temperature, dissolved oxygen (DO), and salinity, almost certainly affect growth and survival at the levels experienced in NC nurseries, but the relative importance of these factors in determining nursery habitat productivity for southern flounder has yet to be determined. Two separate indicators of nursery habitat quality were compared: fish energy content and habitat abiotic conditions. The hypothesis that fish energy content represents the cumulative effect of the abiotic environment on the fish was tested to see if these independent but potentially related indicators could be used in assessments of nursery habitat quality. When measured on appropriate temporal and spatial scales, total fish energy content provided a measurable response of young-of-the-year (YOY) southern flounder to short-term environmental variability, and the results of this study suggest a strong potential for the utility of fish energy content in evaluations of nursery habitat quality for the species. Over a continuous 15 week sampling period from May to August 2006, YOY southern flounder energy content varied weekly in a single nursery habitat by a maximum of approximately 8%, and 51% of this weekly variability in energy content was explained by the weekly variability in temperature and DO measured in this habitat. Across multiple nursery habitats sampled biweekly from May to August 2005, the variability in YOY southern flounder energy content ranged from approximately 12 to 37%. The spatial variability in temperature, DO, and salinity measured across these different nursery habitats was often significant but minimal and did not unequivocally explain the measured variability in fish energy content. The results of this study suggest that fish energy content can provide an unbiased measure of the fish's perception of habitat quality and can be an alternative to other, more labor intensive and potentially biased studies that estimate juvenile growth through field enclosures or micro-otolith analyses. The conclusions of this study and the utility of fish energy content as an indicator of nursery habitat quality are likely applicable to other fish species whose juveniles utilize similar estuarine nursery habitats.
Estimating Run Size of Anadromous Fishes in the Roanoke River, North Carolina, using Hydroacoustics
(2006-08-14) Mitchell, Warren Anderson; Dr. Joseph E. Hightower, Committee Chair; Dr. Jeffrey A. Buckel, Committee Member; Dr. Kenneth H. Pollock, Committee Member
The annual arrival of American shad Alosa sapidissima, striped bass Morone saxatilis and hickory shad Alosa mediocris is ecologically and economically important in the rivers of North Carolina. Both species support commercial and recreational fisheries, and both are the focus of management efforts by state and federal agencies. Reliable information about population levels is essential for effective management. The goal of this study was to estimate the number of adult spawners returning to the Roanoke River. During April-May 2004 and March-May 2005, a stationary 430 kHz hydroacoustic system was deployed on the river bottom in a side-aspect orientation. Tracks of upstream-migrating fish were discernable from ambient noise. The number of fish migrating upstream was slightly lower during 00:00-08:00 compared to the other two 8-hr periods of the day. A majority of fish tracks were within 2 m of the river bottom in both years (89%), and were more associated with ranges near shore. Drift gill netting and boat electrofishing appear to provide an adequate measure of the seasonal presence and absence of target species, though electrofishing provides better samples size. These traditional fisheries methods confirmed the expected seasonal pulses of hickory shad, followed by striped bass, during both years. Counts of upstream fish tracks were low during periods between these pulses. Daytime electrofishing catch rates for 2005 were correlated with daily counts of upstream fish tracks. American shad occurred sporadically at low abundance throughout both years. It was the main target species in this study but made up less than 2% of the catch in both years. A majority of fish captured by gill netting (85%) were within two meters of the river bottom. Analysis methods were standardized in 2005 based on lessons learned in 2004. The 2004 species-specific estimates were 9,046 American shad and 126,176 striped bass. The default estimates (and SEs) for 2005, assuming a uniform cross-channel density of upstream migrants, were 7,054 (450) American shad and 118,778 (4,799) striped bass. Using alternative assumptions about detectability of fish tracks and the cross-channel distribution of upstream migrants, estimates ranged between 5,422 (346) and 13,604 (887) American shad and 94,529 (3,807) and 534,750 striped bass. This first large-scale assessment of the Roanoke River American shad population is difficult to compare with surveys of relative abundance. Estimates of striped bass abundance appear low when compared to traditional stock assessment results. The largest uncertainties regarding the hydroacoustic monitoring is the cross-channel distribution of upstream migrants. For American shad, our study points to the difficulty in assessing the abundance of a target species that is rare in biological samples. Using hydroacoustics to estimate run sizes appears to be feasible, but improvements to the study design are needed. Further validation will improve both accuracy and precision of estimates, and allow fishery managers to use hydroacoustic results with confidence in making management decisions.