Use of a Towed Camera System for Estimating Reef Fish Populations Densities on the West Florida Shelf
Reef fish species tend to reside over high relief habitat which makes them difficult to sample with traditional gears such as nets and trawls. Therefore, implementing and understanding the strengths and weaknesses of new approaches which incorporate acoustic and optical methods has become a priority...
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| Format: | Others |
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Scholar Commons
2014
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| Online Access: | https://scholarcommons.usf.edu/etd/5370 https://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=6558&context=etd |
| Summary: | Reef fish species tend to reside over high relief habitat which makes them difficult to sample with traditional gears such as nets and trawls. Therefore, implementing and understanding the strengths and weaknesses of new approaches which incorporate acoustic and optical methods has become a priority for reef fish stock assessment. Beginning in June of 2013, a towed camera system known as the Camera-Based Assessment Survey System (C-BASS) has been used to visualize over 500 kilometers of transect and record more than 80 hours of video over several habitats in the Gulf of Mexico. Surveys have been completed on the West Florida Shelf in the Florida Middle Grounds (FMG), Madison-Swanson (MS) and Steamboat Lumps (SL) closed areas. High resolution multibeam bathymetry is available for these areas and was important for the deployment of C-BASS which is towed just above the seafloor (2-3 meters above the bottom). This system can facilitate regular surveys of fishes which inhabit untrawlable bottom types (e.g. reefs, pinnacles, boulders) and within habitats where lethal, extractive techniques are prohibited such as in protected areas. To address potential biases resulting from fish reactions towards C-BASS, observed reactive behavior was analyzed in addition to far-field reactive behavior towards C-BASS using stationary camera pods. Most fish observed on C-BASS imagery exhibited weak negative or neutral behavior at proportions of 49% and 38%, respectively. Of those fish which did negatively react to C-BASS, almost all movement was in the 180° and 0° directions (right and left) relative to the tow body's movement. Preliminary results from the direct observation (far-field) experiments also demonstrated a general lack of reactive behavior as C-BASS was towed nearby with no significant decreases in mean abundance of fishes between the periods before, during and after C-BASS was towed over an area (95% confidence level). Although behavioral reactions are species-specific, results indicate that the system may not greatly deter the species of interest (i.e. snappers, groupers, porgies, lionfish, and amberjacks) in this study. Density estimates and subsequent first-order total abundance estimates were also developed for stratified habitat types in the FMG and MS. Overall abundance estimates were greater in 2014 than in 2013 which likely were a result of increased illumination, improvements to video quality, and lower chlorophyll and turbidity levels in 2014. With minor improvements and further behavior analysis, it is expected C-BASS can provide accurate, precise abundance estimates of target reef fish species for management purposes. |
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