Mapping the exposure of the common bottlenose dolphin to environmental and anthropogenic stressors in Maltese waters

Abstract

The common bottlenose dolphin (Tursiops truncatus) is one of the cetacean species regularly found in Malta. However, knowledge on its distribution and on its exposure to the threats caused by human activities remains limited, thus explaining the lack of conservation measures for the species in the region. The identification of areas where human activities are concentrated, and the creation of risk maps contribute to the generation of knowledge that can be used to develop appropriate conservation strategies. To examine the distribution of the common bottlenose dolphin in relation to oceanographic and anthropogenic variables a habitat suitability map was generated using MaxEnt. Subsequently, the map was used to identify areas of high-risk exposure through an overlap analysis with the spatial distribution of vessel traffic and the potential distribution of Fish Aggregating Devices. The study revealed a significant impact of depth and chlorophyll-a concentrations on the distribution of the common bottlenose dolphin, highlighting a strong preference for productive and shallow coastal waters. Furthermore, the overlap analysis indicated that all suitable areas for common bottlenose dolphins are affected by either vessel traffic, fishing, or both. This research establishes a baseline assessment of the common bottlenose dolphin’s suitable habitat and provides insights into its vulnerability to anthropogenic stressors, identifying specific regions where impacts are most pronounced. The results are intended to guide management practices in reducing the species’ exposure to the mentioned stressors.