Quantifying changes in fish habitat use in coastal waters of Louisiana, USA: a hydroacoustic approach

The development of reliable tools for identifying essential fish habitat (EFH) has proven problematic. Knowledge of the distribution and biomass of fishes over discrete habitat types is a prerequisite for effective use of EFH in the management of important commercial and recreational fish species. Resolution of the influence of habitat type and environmental factors on the distribution of fishes is confounded by limitations of traditional sampling gears. To date, hydroacoustic technology has been widely accepted as a tool for surveying fishery resources; however few studies have implemented acoustics in ultra shallow (\u3c2 m) coastal waters. Efforts should be made to utilize hydroacoustics for quantifying changes in fish distributions within estuarine environments given the benefits provided through acoustic technology (e.g. ease of deployment, reduced sampling effort, and non-invasive sampling attributes). A technique was developed for acoustically sensing fishes in the shallow, turbid waters of Barataria Bay, Louisiana. A robust and lightweight remotely-controlled transducer platform was designed for deploying acoustic gear. Sources of scattering within the bay were identified through a series of exclosure net experiments designed to quantify potential effects of plankton and suspended solids on acoustic scattering. Analysis filters were developed to reduce the effects of bubble-induced noise, often observed during periods when wind speeds were greater than 4.5 m s-1. Side-aspect acoustic target strength-length and target strength-weight relationships were derived for tethered individuals of bay anchovy (Anchoa mitchilli) and Gulf menhaden (Brevoortia patronus), with best fit models incorporating data from both species at the lateral perspective. Greater mean fish biomass and fish size were associated with higher salinity and oyster shell habitat in Barataria Bay when compared to nearby soft-bottom habitats. Results of acoustic mobile surveys of the Freeport Sulphur Mine Artificial Reef are presented and illustrate the flexibility and adaptability of the acoustic system for monitoring spatial and temporal changes in fish distributions. I conclude that acoustics can be successfully implemented as a complementary survey technique and can serve as a valuable tool to fishery managers for quantifying fish distributions associated with estuarine habitats