Population estimate and distribution pattern of Indian Ocean humpback dolphin (Sousa plumbea) in an industrialised bay, northwestern Persian Gulf

Monitoring and assessing marine biodiversity relies upon adequate and accurate knowledge of population and distribution patterns of ecologically important species. Cetaceans are recognised both as functionally important and as flagship species and have been the target of monitoring and conservation programs. The habitat specialist Indian Ocean humpback dolphin (Sousa plumbea) is the second most common cetacean in the Persian Gulf. Mousa Bay in the northwestern Persian Gulf is an important, but highly industrialised habitat for this species. We developed a systematic and comprehensive distance sampling survey carried out from 2014 to 2016 to estimate abundance and population density of humpback dolphin in this bay. To evaluate distribution pattern of the species, eight environmental variables were measured and employed in a zero-inflated generalised additive model (ZINB GAM). With an estimated abundance of 92 animals (64-131, 95% CI) and density of 0.123 animal/km2 (0.086-0.176, 95% CI), our results revealed Mousa Bay as one of the largest population of humpback dolphin in northern latitudes of its global range. Based on ZINB GAM findings, distance to coastlines, depth, EC, and chlorophyll a concentration significantly influence the distribution of the species. Our results highlighted that physiographic parameters and resource availability are the most important motivators of the species distribution in shallow nearshore waters. Biotic (e.g. water quality) factors due to strongly being affected by the variability of time and space ranked after physiographic variables. The high tendency of humpback dolphins to enter in highly developed foreshore of Mousa Bay raise the need for conservation-oriented studies to inform conservation planning. This study provides a basis for monitoring humpback dolphin and assessing ecosystem health of northern Persian Gulf.