The Mascarene Islands, identified as an Important Marine Mammal Area


    Violaine Dulau, PhD, Executive Director, Globice & Associate Researcher, Université de La Réunion

    Lana Barteneva, Biologist, MMCO

    Since early 2020, the Mascarene Islands have been identified as an Important Marine Mammal Area (IMMA). In this week’s article Violaine Dulau and Lana Bartheneva review the importance of such demarcation for biodiversity preservation but also as a tool for policy makers and private decision makers to mitigate the impact of their activities in the demarcated areas. Already several important research projects are under way, both in Mauritius and la Reunion, on the population of endangered marine mammals in the area.    


    In early 2020, scientists announced the approval of 37 newImportant Marine Mammal Areas” (IMMAs) in the Western Indian Ocean and Arabian Seas. These IMMAs identify key habitats for marine mammals, including several endangered species such as the Indian Ocean humpback dolphin and the dugong. The delimitation of these IMMAs constitutes an important first step for the conservation of these species. In particular, they could serve as a basis for the implementation of management measures, such as the creation of marine protected areas.

    The identification of IMMAs is based on scientific knowledge and represents the most complete and exhaustive review possible of the distribution of marine mammals and the use of their habitat in the region. Each area of interest is evaluated by the experts on the basis of (1) Vulnerability of the species or population, (2) Distribution and abundance (small resident population, aggregation), (3) Life cycle (breeding habitat, feeding habitat, migration routes), (4) Special attributes (distinctiveness, diversity). Areas that are valued as IMMAs are published on an online eAtlas and can be used to guide effective conservation measures by a variety of stakeholders.

    It is hoped, for example, that industry will be able to use this information to effectively mitigate the impact of their planned activities in these areas, and that governments will be able to use this information to help guide their deliberations on the location of marine protected areas or other coastal zone management efforts.

    As such, the Mascarene Islands (Reunion and Mauritius) and the associated underwater seamounts and banks have been identified as an Important Marine Mammal Area. The area meets several IMMA criteria. It hosts a high diversity of cetaceans, with 22 species of whales and dolphins reported. The inshore waters of Reunion and Mauritius islands sustain small resident populations of Indo-Pacific bottlenose dolphins and spinner dolphins that might be threatened by increase interactions with human activities and coastal habitat degradation.  The coastal waters also represent a breeding habitat for humpback whales. Each year, from June to October, humpback whales are migrating into the area to calve, nurse and mate, using the shallow waters around the islands, but also Le Perouse seamount and Saint Brandon shoal. Further offshore, the insular slope of Mauritius also sustains an important concentration of sperm whales, with groups of resident females and their young being observed year-round.

    Important Marine Mammal Areas
    Map showing the Important Marine Mammal Areas identified in the south-west Indian Ocean.

    The identification of the Mascarenes as an IMMA has been made possible thanks to the research conducted over the last decades by local organizations, such as Globice in Reunion and Mauritius Marine Conservation Society (MMCS) and Marine Megafauna Conservation Organization (MMCO) in Mauritius, and a large-scale aerial survey conducted in the region (REMMOA). Collaborative research programs are ongoing to further assess species diversity in the oceanic waters of the Mascarene which are still largely unexplored.

    In Réunion, GLOBICE is leading a regional program on humpback whales with the aim of increasing our understanding of their movement within the south-western Indian Ocean breeding ground, and their migration routes to their feeding ground in Antarctica. This research program involves the deployment of satellite tags to track individual movement over serval months. Among the main findings of this program, the results have shown that some whales from Reunion are travelling to the Mascarene Plateau, using Saint-Brandon shoals as a breeding habitat. A photo-identification catalogue is also being maintained to identify individual humpback whales and assess their sighting history at the basin scale, based on photographs of their fluke. Research on humpback whale connectivity involves the long-term deployment of acoustic recorders in several locations of the Indian Ocean (Reunion, Madagascar, and along the African coastline) to detect humpback whale song and assess possible exchanges between breeding sites. In 2021, a hydrophone has been deployed in Mauritius waters for the first time, in partnership with Drop of Blue and the Marine Discovery Center, to contribute to this program and further assess connectivity within the Mascarene islands.

    Humpback whale from Réunion
    Humpback whale from Réunion (Photo by Violaine Dulau, Globice)

    In Mauritius, under MMCO leadership the MAUBYDICK Project has been carried out for about 10 years. This Project is aimed at preserving the local population of sperm whales by population estimates, its dynamics, and trends, identifying important habitats. The movement of sperm whales using satellite telemetry and the social structure of the local population are being studied in collaboration with French partners (MEGAPTERA, Longitude 181). The results of the project showed that the resident population of sperm whales is less than 40 individuals, and although the population has a high growth rate, there are signs that the population is very vulnerable. Resident sperm whales spend most of the year in Mauritius waters, time to time visiting the neighboring islands of Rodriguez and Reunion. Migrating sperm whale pods and adult solitary males also visit Mauritius waters. A constantly updated ID-catalog of both resident sperm whales and migratory individuals has been created. Another ongoing MMCO Project, “Whales of Mauritius”, aims to study the species composition of all cetaceans in Mauritius waters and identify important habitats for integration into Marine Spatial Planning and the introduction of mitigation measures. Within the framework of this Project, the mapping of species and their habitats is being carried out, as well as the creation of ID catalogs of small cetaceans, in particular melon-headed whales. In addition to biodiversity conservation, both projects will allow to expand knowledge about cetacean populations and movements in the south-western Indian Ocean through interregional cooperation.

    Charles Telfair Centre is an independent nonpartisan not for profit organisation and does not take specific positions. All views, positions, and conclusions expressed in our publications are solely those of the author(s).

    Main Photo by Hugues Vitry, MMCO

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