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Baited remote underwater video (BRUV) suitability for detecting fish community variation in and out of a marine protected area in Croatia, eastern Adriatic Sea

Baited remote underwater video is a non-destructive method for censusing fish species abundance that is currently under consideration for use in the Mediterranean Sea for monitoring fish stocks and the effectiveness of fisheries regulations. We tested the method in the eastern Adriatic for effectiveness in detecting impacts of habitat degradation and fish harvest on fish abundance, size, and community assembly. A total of 215 BRUVs were deployed at 10 locations during all months from April to September of 2015 and 2016 at and near Kornati National Park (KNP) in Croatia, at benthic habitats including unconsolidated sand/gravel to rocky reefs, with and without macro vegetation consisting of seagrasses Posidonia oceanica, Cymodocea nodosa, or macroalgae Cystoseira species. We analyzed species abundance using generalized linear models with protection or habitat status as fixed predictor factors, location and date of sampling as a random blocking factor, and the maximum number of individuals visible within any single video frame as the proxy of abundance within a species. To estimate asymptotic total species richness we used the Chao estimator, or standard methods of jacknifing or bootstrapping the dataset. We found very highly significant differences in species richness across 10 sampling locations, with the maximum estimated richness within KNP ranging from 53 to 65 (SE 2 to 10), and outside KNP ranging from 24 to 27 (SE 1 to 2). In addition, we find significantly higher species richness associated with structured and edge habitats, such as rocky reefs, and lower richness associated with uniform seagrass or anthropologically degraded habitat. Taxa found more abundant inside the MPA include species heavily targeted by local fisheries, such as Diplodus species, Spaurus aurata, Dentex dentex, Mullus surmuletus, and schooling pelagic genera such as Spicara. We conclude that BRUV has power to detect responses of individual species both to harvest, and to human habitat disturbance, and can assist in testing hypotheses about fish community assembly in the Adriatic Sea. This work was supported by the Croatian Science Foundation under the project COREBIO (3107).

Baited Remote Underwater Stereovideo, fish community assembly, generalized linear models, asymptotic total species richness, marine protected areas

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