Distribution and Abundance Patterns of Several Reef Fish Species Among Different Hard Bottom Habitats in the NE Gulf of Mexico

Hard/live bottom habitat is widespread on the northern West Florida shelf (WFS) in the NE Gulf of Mexico and varies widely in relief, rugosity, morphology, density, area, and in density and composition of attached biota. The community structure, densities, and demographics of reef fishes often vary among these different forms of hard bottom.  The NMFS Panama City lab has conducted a fishery-independent survey of reef fishes since 2005 on the northern WFS between 6 and 40 m using chevron fish traps and stationary video and stereo cameras.  Besides providing annual indices of abundance of exploited reef fishes, the survey also yields data on habitat, community structure, bathymetric and geographic distributions, and habitat associations of reef fishes.  Although WFS reef habitats form a continuum and do not fall into nice, discrete categories, we classified each reef sampled into one of four general types – gorgonian/sponge, scattered, solid, and ledge -  based on a mostly qualitative assessment of relief, continuity of the exposed rock, and the density of attached biota.  Video analysis consisted of noting the maximum number of a given species viewed in any one frame during 20 minutes of a 30 minute recording (commonly called a min count).  Both red and gray snapper were rarely observed over sponge/gorgonian habitat in Apalachee Bay but were very common over more rocky, higher relief reefs in the same region; mean video counts were ~10 fold higher and CV’s were ~70-75% smaller in the latter vs the former area.  Only 7% of sites sampled in Apalachee Bay in 2009 were classified as ledges, but 33% of all gray snapper sightings were on that habitat.  Gray triggerfish showed obvious differences in their affinities for ledge vs gorgonian/sponge reefs, occurring on 85% of the former but only 24% of the latter.  In depths <24 m in Apalachee Bay, frequency of occurrence of scamp, red snapper, gray snapper, and gray triggerfish was roughly twice as high on ledges as on the other three habitats; while black sea bass showed the opposite pattern, with frequency of occurrence 4-6 times higher on gorgonian/sponge, scattered, and solid reefs than on ledges.  Although habitat effects on fish distribution, abundance, and demographics are difficult to identify - often being confounded with effects of depth, fishing effort, and ontogenetic movements - knowledge of these effects is critical for more cost efficient surveys and more accurate stock assessments.