The capacity of imaging sonar for quantifying the abundance, species richness, and size of reef fish assemblages

Reef fish assemblages across tropical and temperate latitudes are increasingly threatened by human impacts and climate change. Accurate and efficient survey methods are essential for quantifying these communities to inform management strategies. Imaging sonars (ISs) are high-frequency acoustic devices that produce camera-like images of objects. Unlike optical instruments, IS functions effectively in turbid and dark water and has proven valuable in detecting fishes in poor visibility and at night. Abundance, species richness, and fish size are desirable metrics in most reef fish surveys. This review investigates previous attempts to quantify these metrics using IS across different habitats. These metrics are often quantified in comparison with alternative methods (e.g. cameras, extractive techniques). This review examines the causes of agreement or incongruence between estimates from IS and estimates from these alternatives. Any instrument employed to quantify reef fishes should be able to operate in structurally complex habitats, and thus the ability of IS to function in these circumstances is also reviewed. Finally, 5 notable limitations of IS are described and solutions discussed. Overall, this review underlines the net value of IS for surveying reef fishes but advises using alternative methods to complement IS estimates of abundance, species richness, and fish size.