Location: Kornati Nacional Park, three locations: islands Mana, Šilo Velo and Kurba Vela
We tested the hypothesis that different species of demersal fish prefer different depths and habitats
A video supported diver visual census was designed to enable the observation and video recording of individual fish along underwater transects within Kornati National Park, and match each fish with the habitat it was observed in and the depth at which the occupied habitat patch was located. At each location, the fish was recorded along one continuous transect which spanned the distance between shoreline and 10 to 12 meter depth repeatedly along a total shoreline length of 1 km within 1 hour observation period. Fish were recorded using a diver operated stereo-video system. The resulting video was coordinated with the depth measuring device so that each fish observation was matched with the bottom type and depth at the time of observation. For each transect, a complete video analysis estimated the relative abundance of fish species, bottom-types, and depths and their combinations.
It was discovered that majority of the 22 sufficiently common fish species preferred mixed rock habitats with boulders and steps of diverse sizes and that 53% of these species were second most common at the edge of Posidonia transitioning with mixed rock. It was also identified some truly Posidonia-associated species and species that strongly prefer rare habitats, like highly heterogeneous areas featuring rock, Posidonia, sand and sponge cover.
From those observations it can be concluded that fish assemblages do differ across major habitats, like Posidonia interiors vs. nearshore mixed rock assemblages. In addition, it was discovered that habitat heterogeneity is attracting high fish richness. While some fish seemed highly selective, others may distribute according to a free distribution across all habitats determined by relative availability.
The information gained from this study will contribute to our knowledge of fish distribution in Kornati National Park and can inform the placement of no-take areas in the future as to effectively promote fish diversity as well as protect vulnerable species.