Preliminary results of 2021 and 2022 Sousa teuszii surveys in the Saloum Delta, Senegal

The Saloum Delta, Senegal, is an inverse estuary with three main channels and an intricate network of secondary channels that increase in salinity with distance from shore. Small boat surveys were conducted from 9-29 July, 2021, and again from 18 March-6 April, 2022 with the aim of documenting the distribution, habitat parameters, and relative abundance of Critically Endangered Atlantic humpback dolphins (Sousa teuszii or AHD). The 2021 survey documented a total of 14 sightings over 12 days of effort, with the majority of sightings clustered in the Saloum ‘River’ in the northern portion of the delta. The 2022 survey documented a total of 22 sightings over 16 days of effort, again with the vast majority of sightings in the main Saloum River. Group sizes over both years of survey ranged from 1-30 with a mean estimated group size of 9 individuals. Depth at sighting locations ranged from a minimum of 2.4 m to a maximum of 15 m, with a mean of 9 m. Surface water temperature ranged from a minimum of 25⁰ C to 33⁰ C, with a mean of 29⁰ C. Salinity readings taken at sighting locations ranged from a minimum of 34 ppt to a maximum of 42 ppt with a mean of 38 ppt. Thousands of photographs were taken and are currently being processed in order to establish a Saloum Delta AHD photo-identification catalogue that can be used to monitor individual dolphins’ movements over time and to generate absolute abundance estimates using mark-recapture models. While formal comparison between 2021 and 2022 photos has not yet been conducted, at least two re-sights of photographed individuals have been documented between 2021 and 2022. Fieldwork included the deployment of one SoundTrap ST500-STD and one LF-POD in July 2021, and two LF-PODs and one SoundTrap ST500-STD in 2022. Analysis of data collected in 2021 is currently underway, with initial indication that both devices recorded dolphins. Fieldwork also included classroom based and hands-on training in cetacean survey methodology for Senegalese, Gambian, Mauritanian, Cameroonian and Nigerian colleagues, as well as collaboration and awareness-raising with managers and staff from the Delta Saloum National Park and five of the Marine Protected Areas in the Delta.