Ranging patterns and mortality of an at-risk marine mammal resident in a highly urbanized estuary

Understanding the ranging patterns of wildlife populations can help identify potential factors contributing to stress, injury, reduced reproductive success, deteriorating health, mortality and displacement from or avoidance of biologically important areas. This study used photographic identification data collected over a 33-year period to characterize the ranging patterns of the Near Threatened Indo-Pacific bottlenose dolphin, Tursiops aduncus, inhabiting the highly urbanized Port River estuary in South Australia. Using kernel density methods, we assessed if ranging patterns differed in size and location by sex and if they were associated with a recent increase in dolphin mortalities. Three locations within the study area were identified as core areas of use for multiple individual dolphins over the 33-year period. The ranging patterns of frequently sighted individual dolphins showed no significant differences in core and representative range size and location by sex, or whether a dolphin was deceased or still alive in the study area. In contrast, dolphins that recently died (2018–2022) had core areas of use concentrated in a single, restricted region of the study area. These core ranges were smaller than those of other individuals in the population, highlighting a potential spatiotemporal component to the recent increase in dolphin mortalities. Subsequent research on potential stressors associated with this dolphin core area of use should aid in the identification of contributing factors to the recent mortalities and assist conservation management decisions. This study highlights the significance of long-term monitoring and understanding wildlife ranging patterns in identifying potential human–wildlife conflicts.