Abundance estimation, group dynamics, and residence patterns of Indian Ocean humpback dolphin ( Sousa plumbea ) in the Dayer-Nakhiloo Marine National Park, Northern Persian Gulf, Iran

The Persian Gulf is positioned in the heart of the Middle East as one of the most critical water bodies. Indian Ocean humpback dolphins ( Sousa plumbea ) are distributed in nearshore waters and are therefore highly vulnerable to a variety of anthropogenic pressures. To our knowledge, there is a little information and data available about habitat use and abundance of this endangered species in Iranian waters. In the present study, baseline data about population size and site fidelity of Indian Ocean humpback dolphins in the Dayer-Nakhiloo Marine National Park in Northern Persian Gulf, Iran, has been explored for the first time. From March 2014 to December 2018, 127 boat-based surveys and 6436 km of survey effort were conducted. Overall, 127 groups of humpback dolphins were observed on 62% of the surveys. Humpback dolphin group size ranged from 1 to 14 individuals (mean 5.8 ± SE 0.3). Abundance estimates were calculated and fitted with open population models. Thirty (95% CI 22–38) humpback dolphins were estimated to inhabit the study area. There was a lack of seasonality in the occurrence of humpback dolphins and strong site fidelity within the Dayer-Nakhiloo Marine National Park. Most of the identified individuals used the study zone regularly (79.5%), while a smaller number were present less often. The results of this study provide important baseline information about humpback dolphin ecology in an area subject to significant anthropogenic pressures which can help to take effective conservation and management measures.