Cetacean diversity of Mauritius

Abstract

There is limited information concerning the cetaceans inhabiting the coastal waters of Mauritius. This document 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 1246 hours 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 was 0.025 cetacean sightings/km. Over the total study period 13 species were recorded from 1459 sightings. Species included: Megaptera novaeangliae, Stenella longirostris, Tursiops aduncus, Tursiops truncatus, Globicephala macrorhynchus, Stenella attenuata, Physeter macrocephalus, Mesoplodon densirostris, Feresa attenuata, Peponocephala electra, Grampus griseus and Ziphius cavirostris. In addition, there were strandings of Kogia sima and Ziphius cavirostris. 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 to 0.25 in 2014. The Shannon index value for the 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 the presence of resident sperm whales.

note on humpback whales (Megaptera novaeangliae) in the central Indian Ocean

“…In addition, an individual seen in the Red Sea, to 26°N in September and October 2016, was thought likely to be a SWIOHW, based on the extent of its white pigmentation (Notarbartolo di Sciara et al, 2017). We also note that the seasonality of occurrence in the central Indian Ocean (with just a few individuals recorded in June, a peak in August-September and none after October) closely matches the seasonality of occurrence of SWIOHW wintering within the southwest Indian Ocean (Braulik and Stern, 2020;Dulau-Drouot et al, 2012;Trudelle et al, 2018;Webster et al, 2020) as does the seasonality of calf occurrence.…”

Spatio-temporal trends in cetacean strandings and response in the south-western Indian Ocean: 2000-2020

“…Southern right whale strandings were exclusively reported in South Africa and thus reflect the documented distribution of the species Best, 2004a, 2004b). Sperm whale strandings occurred in all countries/territories included in this study and closely correspond to previously reported sightings for this species (e.g., Berggren, 2000;Kiszka et al, 2006;Dulau et al, 2008;Webster et al, 2020;Cerchio et al, 2022). All sperm whale strandings were single individuals and occurred in every season.…”

“…Temporal factors (e.g., breeding season, residency patterns, etc.) and anthropogenic pressures may partially explain the pattern of stranding events reported here (Jackson et al, 2015;Webster et al, 2020;Dudhat et al, 2022;Piwetz et al, 2022;Russell et al, 2022). The seasonal analysis revealed that strandings occur throughout the year, but the stranding peaks differed between mysticetes and odontocetes.…”

“…The SWIO contains a high diversity of cetaceans (Findlay et al, 1992;Kiszka et al, 2007;Dulau-Drouot et al, 2008;Pompa et al, 2011;Amir et al, 2007;Dulau-Drouot et al, 2012;Braulik et al, 2017;Laran et al, 2017a;2017b;Webster et al, 2020;Mwango'mbe et al, 2021;Cerchio et al, 2022). At least 29% of globally recognised cetacean species (n = 92) inhabit these waters (Committee on Taxonomy, 2022).…”