Improving visual biodiversity assessments of motile fauna in turbid aquatic environments

Current knowledge of turbid coastlines relies heavily on extractive sampling methods with less destructive visual techniques limited primarily by underwater visibility. Baited Remote Underwater Video (BRUV) is now a commonly used nonextractive sampling technique which involves the use of bait to attract motile fauna to the field of view of the camera, but its use is restricted to clear water environments. Here, we describe and test the addition of a clear liquid optical chamber (CLOC) to a BRUV system to improve underwater visibility when observing motile fauna in turbid waters. The CLOC method was trialed with respect to the ability of the system to identify taxa to species level in both controlled laboratory and field conditions across gradients of underwater visibility. This study found that the introduction of a CLOC to a conventional BRUV system significantly improved the ability to observe identifying features of four fish species in a controlled low-visibility environment (p <= 0.001). The ability to identify taxa to species level in field conditions was also significantly increased with the addition of a CLOC (p <= 0.01). We conclude that the introduction of a CLOC to a conventional BRUV system is a reliable way of improving underwater visibility when assessing motile fauna allowing for a more consistent identification of taxa to species level. This system may be applied to both marine and freshwater aquatic environments.