Cetacean diversity of Mauritius

Abstract

There is limited information concerning the cetaceans inhabiting the coastal waters of Mauritius. This paper details the sightings of cetaceans encountered during April 2008-September 2014. Boat-based surveys were conducted throughout the year, primarily focusing on spinner and bottlenose dolphin populations that are important for the local dolphin-watching industry. More than 1,246hrs over 749 days of surveys were spent searching for cetaceans. All cetaceans encountered were recorded. During 2013 and 2014, dedicated diversity surveys were conducted and 2443.6km of search effort was covered around the islands. The encounter rate for this period was 0.025 cetacean sightings/km. Over the total study period 13 species were recorded from 1,459 sightings. Species included: humpback whales; spinner dolphins; Indo-Pacific bottlenose dolphins; common bottlenose dolphins; short-finned pilot whales; pantropical spotted dolphins; sperm whales; Blainville's beaked whales; pygmy killer whales; melon-headed dolphins; Risso's dolphins; and Cuvier's beaked whales. In addition, there were strandings of dwarf sperm whales and Cuvier's beaked whales. The most common species encountered were spinner dolphins, Indo-Pacific bottlenose dolphins, humpback whales and sperm whales. As expected, only humpback whales showed any seasonality in monthly encounter rates (Kruskal-Wallis H = 42.39, Hc = 54.25, p < 0.001). The overall Shannon diversity index was 0.58 (95% CI 0.57-0.60) though this ranged between 0.77 in 2009 and 0.25 in 2014. The Shannon index value for the 2013-2014 diversity study was 0.83 (95% CI 0.74-0.91). This study demonstrates the richness of the waters around Mauritius and the importance of the area for beaked whales, migrating humpback whales and resident sperm whales.