An innovative sampling protocol for fish species identification methods in shallow waters: towed diver, towed video and stereoscopic camera system

The European Marine Strategy Framework Directive (MSFD) requires the achievement of the good ecological state of all the component of the marine environment, including fish in coastal waters. It required surveying the coastal fish and cephalopods. The ACaPELA (ACoustic PELAgic) project aims to describe pelagic fish populations in shallow waters using active acoustic. One of the main issue of acoustic programs is to identify species associated with acoustic detection remains difficult, particularly in shallow waters with high species diversity. Innovative procedures for the specific allocation of echo trace are needed and tested in this study: one method based on “free divers” consist in divers searching for schools or aggregations and another based on “towed diver”. Video was also deployed to create a ground truth for both methods. In addition, we used a stereoscopic video system that allows us to assess size and abundance measurements and compare them with the divers’ estimations. The towed diving method shows an advantage in the implementation, the amount of acoustics ground truth acquired. The use of stereoscopic video shows that it can be used to overcome the diver and carry out precise measurements of individuals, but its use in a monitoring program should be based on automated video processing tools in order to limit processing time. However, with the today increasing advances in imaging analysis, our results suggest that autonomous system like a towed and remotely controlled submarine glider could be operational in the very near future.