Assessing marine traffic and related pressures and threats to cetacean populations to support vessel management in the Mascarene Important Marine Mammal Area

Abstract

The global growth of marine traffic, among many growing anthropogenic threats, is of particular concern for marine mammals. Assessing the co-occurrence of marine traffic and cetacean distributions provide useful information for understanding the spatial extent and level of pressures and threats posed by vessels. Regional and local marine traffic is increasing within the territorial waters of Réunion Island, included in the Mascarenes Important Marine Mammal Area. This study provides the first description of the spatial distribution of vessels within these waters using Automatic Identification System (AIS) data and provides an assessment of the pressures and threats vessels may pose to five cetacean species (the spinner dolphin, the Indo-Pacific bottlenose dolphin, the common bottlenose dolphin, the pantropical spotted dolphin and the humpback whale). We found that vessels occurred in all Réunion waters and identified two highly-used shipping corridors on either side of the island. Our results highlighted areas of potential threats from marine traffic for each of the five species. These areas mostly mirrored their preferential core habitats, which raises concerns, especially for the resident and most vulnerable species. Given the increase in marine traffic in the western Indian Ocean region, this study provides additional information in support of an ongoing French initiative to implement an “Area to Be Avoided” in Réunion waters, in order to improve safety and security while also benefiting to cetacean conservation.