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

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Stephanie Plön
Stephanie Norman
Pierre-André Adam
Norbert Andrianarivelo
Santosh Bachoo
Gill Braulik
Tim Collins
Vanessa Estrade
Owen Griffiths
Gelica Inteca
Nasreen Khan
Sophie Marinesque
Emma Mederic
Michael Mwang’ombe
Jennifer Olbers
Lea Ramoelintsalama
Katie Reeve-Arnold
Diana Rocha
Angie Gullan
Anjara Saloma
Els Vermeulen
Hugues Vitry
Chris Wilkinson
Violaine Dulau


The south-western Indian Ocean (SWIO) is a region of global importance for marine mammal biodiversity, but our understanding of most of the species and populations found there is still rudimentary. The Indian Ocean Network for Cetacean Research (IndoCet) was formed in 2014 and is dedicated to the research of all cetacean species across the SWIO. Since 2019, there have been efforts to create a regional network for coordinated response to stranding events as well as training and capacity building in the SWIO region. The present analysis represents a first investigation of stranding data collected by various members and collaborators within the IndoCet network, covering over 14,800km of coastline belonging to nine countries/territories. Between 2000-2020, there were 397 stranding events, representing 1,232 individual animals, 17 genera and 27 species, belonging to six families: four balaenopterids, one balaenid, one physeterid, two kogiids, six ziphiids and 14 delphinids. Seven mass strandings were recorded: two were composed of three to 20 individuals and five composed of >20 individuals. Spatial analysis of stranding events indicated that local spatio-temporal clusters (excessive number of events in time and geographic space) were present in all countries/territories, except for the Comoros. The only significant cluster was detected on the southwest coast of Mauritius, just west of the village of Souillac. The SWIO region predominantly comprises relatively poor countries/territories, but imminent Blue/Ocean economy developments are prevalent throughout the region. This study highlights the importance of establishing baselines upon which any future potential impact from anthropogenic developments in the region can be measured.

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