Abstract

Traditional methods used to assess oyster reef distribution and condition are only able to provide subjective point information which is often poorly georeferenced. Maps of oyster habitat in shallow waters are there fore typically extremely generalized, giving few details about the true distribution, character and dynamics of reefs. Sides can sonar offers a significant advantage for oyster reef assessmentin the turbid waters of coastal Louisiana. We used sides can sonar in ultra-shallow (<2m) waters to completely image oyer 19 000 ha in Louisiana estuaries inadyance of an impending freshwater diversion project. We also conducted four years of intense annual surveys in a more restricted area (320 ha) with a diversity of reef types and culture intensity to examine natural and anthropogenic impacts on oyster reef extent and character. Our intensive surveys identified older stable reefs which had not been actively worked. Shell abundance and structure on these reefs were high, but oyster meat productivity was low. Areas of intense oyster culture were characterized bylow relief reefs that frequently showed distinct evidence of scarring from dredging and other anthropogenic sources. Smaller scars caused by oyster dredging typically healed through the within time period of our studywhile larger anthropogenic scarring did not diminish over the four years. We also deployed the sonar towfish over an area immediately before and after both seeding and harvesting to establisha quantitative relation ship with sonar reflectance. These relationships can be further used to predict the impact of harvesting and seeding on the extent oyster habitat. Demographic comparison of red snapper (Lutjanus campechanus) from the Atlantic and Gulf of Mexico.

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