Population and conservation status assessment of Mozambique dugongs (Dugong dugon)

Abstract

The dugong (Dugong dugon Müller, 1776) is a long-lived marine mammal that is widely distributed along coastal regions of the Indo-Pacific Ocean. Dugongs typically inhabit warm, shallow water, coastal ecosystems in tropical and subtropical regions, with notable populations being found off the north coast of East Africa (Red Sea), in the Arabian Gulf and northern parts of Australia. Seagrass meadows are considered as critical habitats. Dugongs are listed as vulnerable to extinction throughout their global distribution range as they are heavily impacted by human activities, which have contributed to population declines over the last six decades. The dugongs found in and around the Bazaruto Archipelago, Mozambique, are considered the last, viable subpopulation in the southern reaches of the West Indian Ocean region. The Mozambique subpopulation, recognised as part of the ‘critically endangered’ East African subpopulation, is thought to number between 200 and 325 individuals at present. The conservation of this subpopulation, therefore, is critical to dugong survival in the region. This research employed molecular techniques to investigate the genetic diversity, degree of isolation and phylogenetic relationships between dugong subpopulations in the West Indian Ocean region. The first data chapter (Chapter 2) assessed nucleotide and haplotype diversity indices within the Mozambique subpopulation using two mitochondrial markers (the control region [D-Loop] and the cytochrome b [CYTB] gene). Genetic analyses revealed extremely low mitochondrial nucleotide diversity (π), with the D-Loop marker proving to be more efficient at determining estimates of genetic diversity (0.0014), compared to that of the CYTB gene (0.0003). In particular, four haplotypes were identified in the D-Loop region while only two haplotypes were identified in the CYTB region. The second data chapter (Chapter 3) investigated the genetic diversity of dugongs throughout the greater West Indian Ocean region, and assessed the degree of genetic similarity, variation, gene flow and isolation between populations/bioregions (Mozambique, Madagascar/Comoros Islands, South West Indian Ocean, North West Indian Ocean, Arabian Gulf). The findings revealed weak genetic structuring and little genetic differentiation throughout the five recognised seagrass bioregions in the West Indian Ocean region, with nucleotide diversity (π) indices ranging between 0.0048 and 0.0337. Moreover, the Mozambique subpopulation of dugongs was not found to be genetically isolated. Overall, my findings indicated extremely low genetic diversity within the Mozambique dugong subpopulation, suggesting the immediate need for effective conservation and management interventions. Conserving this subpopulation will be crucial for the long-term survival of East African dugongs, as successful initiatives may encourage self-seeding and population recovery across the region over time. It is recommended that continued research and further mitochondrial analysis using a larger sample size, or the novel technique of environmental DNA (eDNA), be undertaken to gain a more comprehensive and accurate description of the population genetic structure of dugongs in the Mozambique seascape and surrounding regions.