###### Abstract
Fish biodiversity in French Guiana is very high, but only a few species are of commercial importance: Silariformes Ariidae (_Sciades proops_), Perciformes Sciaenidae (_Cynoscion acoupa_), Lutjanidae (_Lutjanus vivanus_), Scrombidae (_Acanthocybium solandri_), Haemulidae (_Genyatremus luteus_) and Serranidae (_Epinephrine tiajara_). _Epinephrine tiajara_, commonly named the poliation grouper, is a demersal species that inhabits bays, estuaries, mangroves, artificial reef and rocky sites, inshape as well as offshore [30; 31; 32; 33]. It is a valuable commercial fish species in French Guiana when, at the time of the study, it was protected in other countries and listed as a critically endangered species in the IUCN red list, principally because of overfishing [34]. In the vicinity of the Grand Connetable Islands, classified as Marine Protected Area in 1992, fishing is forbidden, so the fish and marine bird species are protected. From a fish population management perspective, following and understanding the dynamics of the fish population is the first step to regulation policy. However, the marine waters of French Guiana present extreme turbidity, not only inshore due to the influence of local rivers (Approuague, Mahury) [35; 36; 37] and the resuspension of mudflat sediments [35; 36; 38] but also offshore due to the Amazon River, the world's most turbid region with a diffuse attenuation coefficient (\(K_{d}(490)\)) superior to 5 \(\,\mathrm{m}^{-1}\)[39]. Indeed, the largest river of the world discharges nearly 100 million tons of sediment in marine waters per year [40], which is then carried along the French Guiana coasts up to the Caribbean Sea [41] via the north Brazil current [42]. Therefore, the extremely turbid conditions of the near-shore marine environment of French Guiana limit the possible methods to study fish distribution or abundance and knowledge on the local fish ecology is scarce. The objective of this study was to evaluate the reliability of the P900-130 BlueView acoustic camera to study fish population ecology, including identification, abundance, spatial distribution and size structure in extreme turbid conditions in order to apply this methodology for annual fish population survey  
An ideal demersal species for evaluating acoustic camera capabilities under low visibility is the poliath grouper. This species has morphological (maximum length of 2.50 m) and ecological characteristics that could facilitate (1) its identification through acoustic beam as well as (2) the approximation of the total abundance of the local population. Indeed, goliath groupers are strongly linked to their rocky habitat with really short daily distance movements [32], except during reproduction periods [43; 44]. Therefore, by implementing an exhaustive survey of rocky sites, the total counted individuals approximate the total abundance of the local population. Moreover, a scientific fishing survey led simultaneously allowed studying the consistency of the acoustic camera results compared to usual fishing surveys. The present study aimed at (1) investigating the possibility of identifying demersal fish species through an acoustic camera, (2) analyzing replication and accuracy of abundance and total length estimations with acoustic cameras and (3) comparing spatial distribution provided from fishing data and acoustic camera. The final purpose was to know if acoustic cameras would be efficient tools to realize spatial and temporal surveys of demersal fish populations.