Remote drifted and diver operated stereo–video systems: A comparison from tropical and temperate reef fish assemblages

Underwater visual census methods for sampling reef fish that use scientific divers are common and can be effective in shallow water habitats. There is an ongoing need to develop methods that can sample reef fish assemblages in a similar manner, but at depths that are unsafe or inefficient for scientific divers using conventional SCUBA equipment. This study aimed to assess the limitations and biases associated with a drifted stereo–video system (Drifter) by comparing data collected with a diver operated stereo–video system (stereo–DOVs) at the same locations. The composition, number of species, total abundance and the abundances of dominant reef fishes were compared across the two sampling techniques at three temperate and three tropical reefs. There were no significant differences between the compositions of the assemblage sampled by each technique at either the temperate or tropical reefs. There was significantly higher dispersion in the data collected by the Drifter. This higher dispersion was most likely caused by the combined effects of low vehicle stability, the positioning of the drifter higher in the water column in comparison to the stereo DOVs and the challenges associated with navigating the drifter along narrow and fragmented reefs. The stereo–DOVs sampled more species of fish and more individuals than the Drifter. No significant differences were detected in the abundance of any of the dominant species. The Drifter provides a comparable technique to stereo–DOVs, without the depth and time limitations inherent to that system. The high dispersion of the data, low number of species and lower number of individuals sampled by the Drifter result in a slightly lower statistical power from an equivalent sampling effort when compared to stereo–DOVs. Future developments which will help overcome these differences are discussed.