## 3 Results  
### Demersal Species Identification Through Acoustic Camera  
Several demersal species, when moving, were detected with the acoustic camera. Identification of species having a distinguishable silhouette, such as rays, marine turtles, and sharks (Figure 4A-C, respectively), could be identified easily, whereas fish with a typical fusiform shape were more difficult to identify without additional information (Figure 4D). For this reason, important work on methodology development was done to identify the targeted species among other fish species.  
Figure 4: Detection of a ray (**A**), a marine turtle (**B**), a shark (**C**), a goliath grouper (_Epinephrine tubjara_) with its corresponding acoustic shadow (**D**) and scheme of the determination of the fish position in the water column (**E**) with a P900-130 BlueView acoustic camera.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**2011**} & \multicolumn{6}{c}{**2012**} \\ \cline{2-10}  & \multicolumn{2}{c}{**Acoustic Camera Survey**} & \multicolumn{3}{c}{**Fishing**} & \multicolumn{3}{c}{**N Survey**} & \multicolumn{3}{c}{**Acoustic Camera Survey**} & \multicolumn{3}{c}{**Fishing**} & \multicolumn{3}{c}{**N Survey**} \\ \cline{2-10}  & **Mobile** & **Stationary** & **Total** & & & **Mobile** & **Stationary** & **Total** & & \\ \hline Mamelles & 3 & 17 & 20 & 5 & 7 & 18 & 0 & 18 & 7 & 8 \\ La Mère & 33 & 0 & 33 & 1 & 3 & 17 & 0 & 17 & 2 & 4 \\ Le Pérez & 23 & 14 & 37 & 3 & 5 & 39 & 6 & 45 & 3 & 4 \\ Malignere & - & 0 & 0 & 1 & 2 & 6 & 0 & 6 & 1 & 3 \\ TOTAL & Rénire & 59 & 31 & 90 & 10 & 17 & 80 & 6 & 86 & 13 & 19 \\ Islands & 26 & 0 & 26 & 15 & 19 & 29 & 7 & 36 & 3 & 10 \\ Petri Constable & 93 & 8 & 101 & 105 & 2 & 31 & 10 & 41 & 65 & 1 \\ Grand Constable & 119 & 8 & 127 & 120 & 21 & 60 & 17 & 77 & 68 & 11 \\ Island MPA & **TOTAL** & **178** & **39** & **217** & **130** & **38** & **140** & **23** & **163** & **81** & **30** \\ \hline \hline \end{tabular}
\end{table}
Table 2: Number of goliath groupers counted around rocky sites using the acoustic camera and fishing in 2011 and 2012. N survey: number of fishing trips.  
Adding to morphological criteria of the acoustic signal and the silhouette of the acoustic shadow, other parameters could be considered in identifying species, such as (1) the behavior of the fish (swimming or aggregating behavior), and (2) the depth of the fish, evaluated from the fish signal position in relation to the acoustic video scale (see on Figure 4E). In this way, goliath groupers were identified in acoustic images using four combined morphological and behavioral characteristics: (1) body width relative to the length of the species produces a massive acoustic image, bulkier than other species, (2) length of fish tends to be large (up to 2.50 m), especially compared with other grouper species (<40 cm) living in similar habitats, (3) swimming behavior, because grouper show a distinctive swimming style with slow tail undulation relative to other fish that could reach a similar size like mackerel (_Scomberomorus_ sp.) or tarpen (_Megalops atlanticus_) and (4) the depth of occurrence (near the bottom) since other fish species do not use the same area of the water column (pelagic fish). Thus, with prior knowledge of fish species silhouette, their behavior and the depth of occurrence, it was possible to identify fish species from acoustic images. However, because of the difficulty of distinguishing very small individuals (<40 cm) from other species, they were not included in the present study.  
Seven individuals with a characteristic acoustic image showing obvious morphology, slow swimming behavior, large size and a demersal position were caught on rocky study sites during the combination of both acoustic camera and fishing surveys. All seven were confirmed as goliath groupers. No other fish were caught during these combined surveys.