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.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-07052006-223946 |
| Date | 14 August 2006 |
| Creators | Mitchell, Warren Anderson |
| Contributors | Dr. Joseph E. Hightower, Dr. Jeffrey A. Buckel, Dr. Kenneth H. Pollock |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-07052006-223946/ |
| Rights | unrestricted, 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. |
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