Measuring niche overlap between co-occurring Plectropomus spp. using acoustic telemetry and stable isotopes

Investigating niche overlap in exploited fish species can reveal behavioural information necessary to improve conservation and fisheries management at a species level. The present study examined spatial and dietary overlap between two co-occurring reef fish, namely Plectropomus leopardus and P. maculatus, at an inshore reef in the Great Barrier Reef Marine Park using acoustic telemetry and stable isotopes. Movements of tagged fish within an acoustic array of 19 receivers deployed along a narrow reef portion of Orpheus Island were monitored for up to 3 years. Although space use was similar between species, spatial overlap was rare and P. maculatus (n = 30) was consistently deeper than P. leopardus (n = 32). Dietary overlap between species was high based on overlapping delta N-15 and delta C-13 isotopic niches in muscle tissue (n = 20). The complementary stable isotope and acoustic telemetry data revealed these species had similar isotopic niches but distinct space use patterns, which may be a product of competition for resources. These findings show species-specific behaviours within a genus commonly managed or reported as a single entity, and provide new information on partitioning of resources by Plectropomus spp. in inshore reef environments.