Performing fish counts with a wide-angle camera, a promising approach reducing divers' limitations

•The first attempt to evaluate the potential of an underwater wide-angle camera (UWC)•Minimal differences are found between traditional visual census (UVC) and the UWC.•Both methods have the same consistency and ability to detect fish changes.•UWC field effort was lower than UVC.•Unlike UWC surveys, the diver's presence in UVC had a systematic effect on fish.

Visual standardised methods for census of reef fishes have long been used in fisheries management and biological surveys. However, these tools have inherent sources of bias and the SCUBA divers who perform them are highly constrained in terms of survey time, maximum depth and frequency of sampling. Alternatives like underwater video are thus being recommended in a wide range of configurations. Yet, all these techniques are still limited in field of view, particularly when compared to the ability of a SCUBA diver performing censuses. In this scope, we evaluated the potential of an underwater wide-angle camera (UWC) to survey fish assemblages by testing it against instantaneous underwater visual census (UVC). Our results showed minimal yet significant differences between methods, mainly because of the camera's loss of resolution when under extreme visibility conditions. Both approaches had the same consistency and ability to detect changes in fish assemblages but, to estimate total species richness, the UWC needed less field effort. Moreover, a SCUBA diver performing census had an effect on fish assemblages which introduced differences of greater magnitude than those found between methods. The removal of the diver effect, the proven ability to detect changes in fish assemblages and the verified gain in field effort, pointed the wide-angle camera as a promising tool to perform census of reef fishes.