Little is known about the extent of genetic connectivity along continuous coastlines in manta rays or whether site visitation is influenced by relatedness. Such information is pertinent to defining population boundaries and understanding localised dispersal patterns and behaviour. Here, we use 3057 genome-wide single nucleotide polymorphisms (SNPs) to evaluate population genetic structure and assess levels of relatedness at aggregation sites of reef manta rays (Mobula alfredi) in southern Mozambique (n = 114). Contrary to indications of limited dispersal along the southern Mozambican coastline inferred from photo identification and telemetry studies, our results show no evidence of population structure (non-significant FST <0.001) for M. alfredi along this coast. We also found no evidence that individuals sampled at the same site were more related than expected by chance for males, females or across both sexes, suggesting kinship may not influence visitation pattern
these sites. We estimated the effective population size (Ne) of this population to be 375 (95% CI = 369-380). Comparison to a distant eastern Indian Ocean site (Western Australia; n = 15) revealed strong genetic differentiation between Mozambique and Western Australia (FST = 0.377), identifying the Indian Ocean basin as a barrier to dispersal. Our findings show that genetic connectivity in M. alfredi extends for several hundred kilometres along continuous coastlines. We therefore recommend the population in Mozambique be considered a discrete management unit and future conservation plans should prioritize integrated strategies along the entire southern coastline.
M. alfredi DArTseq SNP data (Diversity Arrays Technology, Canberra)