Complementary Non-invasive Fish Monitoring Distinguishes Depth-Dependent Fish Communities

Abstract

Human activities are increasingly affecting marine environments, with fish communities serving as critical indicators of ecosystem health. Effective management of marine fishes is imperative for maintaining the balance of marine ecosystems, necessitating comprehensive monitoring strategies. We used baited remote underwater video systems (BRUVS) and environmental DNA (eDNA) survey methods to assess fish communities across four offshore islands and seamount groups in Australia's eastern Great Australian Bight (GAB). Employing a paired sampling design, we conducted 32 BRUVS deployments and collected 32 eDNA samples in tandem. We compared the taxonomic and functional diversity of fish detected by these two methods and explored fish assemblage within the eastern GAB. Our findings demonstrated that BRUVS and eDNA data were complementary to each other, with each approach detecting distinct segments of the fish community. Only 17 of the 102 species recorded were detected by both methods and combining these two datasets resulted in a 40% increase in species-level detections compared to either method alone. BRUVS predominantly identified benthic and demersal fish, whereas eDNA predominately identified pelagic species, including species of conservation (e.g., white sharks) and commercial significance (e.g., southern bluefin tuna). Yet, both methods distinguished depth-dependent communities within a single sampling site. These findings emphasize the value of integrating multiple approaches for enhanced fish species detection, offering valuable insights into future biodiversity monitoring and conservation efforts.