Depth Gradient and Habitat Structure-Based Characterisation of Fish Assemblages in Lakshadweep Atolls

The rehabilitation of bleaching-impacted reefs in Lakshadweep is supported by reef fish populations that help regulate algal growth. However, with the increase in reef fishery in these islands, there is a perceived threat of target species decline. Understanding the fish assemblages helps identify the habitat preferability (depth zones, reef facies, etc.) of fish species. Such information is crucial to demarcate management areas to permit or decline fishing targeted fish groups. The present study aimed to gather information on fish assemblages over differing depth gradients and habitat structure. Fish census and species diversity were recorded using belt video transects and camera traps at 5, 10, 15, and 20 m depths from four stations each on the reef slopes of Kavaratti, Kadmat, and Kiltan atolls of the Lakshadweep Islands. The abundance of demersal fishes, particularly Pomacentrids, was notable in the study area, with significant numbers identified across transects. Families like Acanthuridae and Labridae showcased distinct depth-related patterns, with abundance levels shifting in response to changing depths, highlighting the diverse habitat preferences of reef fish species. Island-specific trends in fish abundance and composition were also particularly evident in Pomacentridae, Labridae, and Acanthuridae. Significantly, the study found that the western or lagoon-facing sides of all three atolls harbored different assemblages of fish. These findings show clear demarcation based on depth and reef facies-wise distribution of fish groups, thus helping identify the distribution of target fish groups in Lakshadweep reefs, which can factor as inputs for fishery management.