Benthic Habitats and the Effects of Fishing

Symposium Abstract: Geoacoustic and Geological Characterization of Juvenile Red Snapper Habitat, Northern Gulf of Mexico Continental Shelf

S. J. Bentley, W.F. Patterson, Y. Allen, W. Vienne, and C. Wilson

doi: https://doi.org/10.47886/9781888569605.ch50

Laboratory and small-scale in situ experiments have demonstrated juvenile red snapper display an affinity for low-relief shell-rubble habitat; however, the spatial extent and temporal variability of large-scale shell-rubble features on the Mississippi-Alabama shelf are unknown. Moreover, the seabed geology of the entire region in general is poorly known, with little significant research conducted since the 1950’s. Therefore, to develop a geological understanding of quality juvenile snapper habitat in the region, we have undertaken a program of sidescan seabed mapping and seabed sampling in areas on the northern Gulf of Mexico continental shelf that historically produced high, median, and low juvenile red snapper catch rates in trawl surveys. Preliminary results of sidescan surveys and grab samples indicate highest juvenile snapper catch rates are found near irregular low-relief ridges of shell and sand, with CaCO₃ content to 100%. The ridges are elevated 1-2 m above the surrounding seabed and generally orient along NW-SE axes. Surrounding seabed is more typical of the Holocene transgressive sand sheet, composed of fine-medium muddy sand with shell content <10%. Most shell material found on the ridges appears to be fragments of the oyster Crassostrea (now highly encrusted by epibionts), indicating ridges are of estuarine origin, and are probably remnants of coastal shell reefs formed during the Holocene Transgression (i.e., during the past ~6000 y). Ongoing research focuses on elucidating origin of the ridges, developing a geoacoustic fingerprint for quality juvenile red snapper habitat, and examining temporal and spatial variability in juvenile snapper habitat utilization patterns.