Assessing the genetic diversity of catface grouper Epinephelus andersoni in the subtropical Western Indian Ocean

Epinephelus andersoni is a range-restricted species that is endemic to the south-east coast of Africa from Quissico in Mozambique to Knysna in South Africa. The species is an important commercial and recreational linefish species that is currently considered to be optimally exploited although there have been some signs of depletion within its range. This is likely because of its complex life-history including diandric protogyny and high residency, which make it potentially vulnerable to over-exploitation. This study analysed the genetic structure and diversity of E. andersoni using nuclear (intron 1 S7) and mitochondrial (cyt b) DNA genes for 240 and 269 individuals,respectively, to provide information for fisheries conservation and management. S7-1 allelic diversity was high (0.801) with the AMOVA showing significantly high among group variation (ΦCT = 0.204, p < 0.05) between five groups: 1. Quissico to Inhaca; 2. Cape Vidal to Port Edward; 3 Port St Johns to Coffee Bay; 4. Mbhashe; 5. Port Alfred. This geographic structuring could be attributed to low gene flow across barriers such as the Port Alfred upwelling cell, the Mozambique Channel eddies and smaller more localised upwelling cells such as the Port St Johns cell. Contrastingly, the cytochrome b (cyt b) results indicate low haplotype diversity (0.309) and no differentiation (ΦCT = 0.265, p = 0.074) between groups, supporting the hypothesis of a historical population bottleneck. This may be due to an unusually slower mutation rate of the cyt b region than the S7-1 gene region suggesting more recent diversification. Complex patterns of diversity revealed by this study highlight that a precautionary approach is required for the management of this species that takes into account some regional differentiation, while some connectivity still exists, making it practical to continue to manage E. andersoni as a single stock.