Investigating nocturnal fish populations in situ using baited underwater video: With special reference to their olfactory capabilities

In this study, a novel technique using baited underwater video with infrared lighting was compared with traditional underwater census surveys to investigate fish populations in situ. Fish abundance at the baited underwater video was related to the olfactory capability of each species. Olfactory specialists were shown to arrive at baited underwater video drops earlier, and in greater numbers, than non-olfactory species. This pattern was reversed in non-olfactory species, which were found to dominate underwater census surveys and appear less at baited underwater video drops. The sensory capacity of a species was found to be a larger determinant for fish abundance at baited underwater video drops than was the actual density of that species. The result of this study has ramifications for fish sampling techniques that use chemical stimuli to attract fish species, such as in the deep sea. The baited underwater video technique was highly effective at determining the diel activity of fish species.

► Identifies novel technique for investigating nocturnal fish in situ.
► Modified baited underwater video ideal for determining fish diel activity patterns.
► Using chemical attractants in sampling design overestimates olfactory specialists.