Gag (Mycteroperca microlepis) space-use correlations with landscape structure and environmental conditions

To explore variation in space use under different environmental conditions, we acoustically tagged gag (Mycteroperca microlepis) established on experimental artificial reefs in the Gulf of Mexico and used an acoustic positioning array to record animal positions during the winters of 2007 and 2008. From side-scan sonar imagery, we created a categorical habitat map of the hard- and sand-bottom habitats surrounding the reef. We recorded water conditions using an Acoustic Doppler Current Profiler. Correlations between gag space use (distance from the reef, distance from the seafloor, and travel speed) and environmental conditions (bottom type, time of day, lunar phase, and water temperature, speed and flow direction) showed gag typically using space near, but not directly at the reef. The 50% and 95% kernel density contours fell within 17 and 39m of the reef, respectively, though gag spent the most time about 10m from the reef. All individuals made occasional excursions beyond their primary space-use areas. Gag spent 86% of the time within 2.5m of the seafloor, with periods of frequent or extended movement up to 9m from the seafloor, usually near the reef. On average, gag moved about 25% farther from the reef during the day; correlations with other environmental conditions were weak or unclear. In all cases, variation in space-use among individuals or of particular individuals over time was greater than the variability explained by changing environmental conditions.