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An evaluation and comparison of techniques for estimating fish species composition, abundance and size structure in mangrove and reef habitats
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    "Underwater visual fish surveys have become the most commonly used method for estimating fish abundance and diversity in coral reef environments, and more recently in adjacent environments such as mangroves. Limitations associated with visual surveys (e.g., restricted to daylight hours and relatively clear-water conditions) have resulted in a potentially incomplete assessment and understanding of fish community composition, structure and dynamics. In the present study, we examine the utility of three techniques for underwater fish community assessment. In mangrove and coral reef habitats, under varying conditions of light and water clarity, we compare and contrast: (1) a dual-frequency, multi-beam sonar system (DIDSON); (2) a stereo-video system; and (3) a standard visual survey. Both DIDSON and stereo-video provided relatively precise and similar length estimates, but stereo-video resulted in underestimates of length in turbid conditions, where DIDSON was not affected. Stereo-video resulted in underestimates of abundance, relative to DIDSON, in clear and turbid mangrove conditions. Importantly, DIDSON enable the quantification and measurement of fish swimming within and behind the prop roots of mangroves that were not visible or detected with stereovideo or visual surveys. DIDSON was also effective in environments in which stereo-video was ineffective (at night and in moving transects). Species composition lists generated by stereovideo and visual census were only somewhat similar, and length-frequency distributions generated by all three methods were similar but differed in degree of spread. We discuss the benefits and limitations of each method for assessing fish community structure, and recommend combined survey approaches to maximize our knowledge of fish utilization of mangrove and reef habitats"--Abstract.

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