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Octopus cyanea (Gray, 1849), abundant in the South‐West Indian Ocean (SWIO), constitutes a vital resource for both subsistence and commercial fisheries. However, despite this socioeconomic importance, and recent indications of overfishing, little is known about the population structure of O. cyanea in the region. To inform sustainable management strategies, this study assessed the spatio‐temporal population structure and genetic variability of O. cyanea at 20 sites in the SWIO (Kenya, Tanzania, Mozambique, Madagascar, Mauritius, Rodrigues, and the Seychelle Islands) by complementary analysis of mitochondrial DNA (mtDNA) noncoding region (NCR) sequences and microsatellite markers. MtDNA analysis revealed a shallow phylogeny across the region, with demographic tests suggesting historic population fluctuations that could be linked to glacial cycles. Contrary to expectations, NCR variation was comparable to other mtDNA regions, indicating that the NCR is not a hypervariable region. Both nuclear and mtDNA marker types revealed a lack of genetic structure compatible with high gene flow throughout the region. As adults are sedentary, this gene flow likely reflects connectivity by paralarval dispersal. All samples reported heterozygote deficits, which, given the overall absence of structure, likely reflect ephemeral larval recruitment variability. Levels of mtDNA and nuclear variability were similar at all locations and congruent with those previously reported for harvested Octopodidae, implying resilience to genetic erosion by drift, providing current stock sizes are maintained. However, as O. cyanea stocks in the SWIO represent a single, highly connected population, fisheries may benefit from additional management measures, such as rotational closures aligned with paralarval ecology and spanning geopolitical boundaries. [ABSTRACT FROM AUTHOR]

• The periodic, temporary closure has positive economic benefits to coastal fishing villages. • The timing of octopus temporal closure requires scientific evidence for an effective outcome. • Improving the management of octopus fisheries can deliver endless benefits throughout the octopus supply chain while rebuilding the stocks. [ABSTRACT FROM AUTHOR]

Seascape configuration is known to influence fish distribution and abundance in coastal waters. However, there is little information regarding how the shape of the coastal seascape influences catches of landed fisheries species, particularly so in the understudied western Indian Ocean (WIO). With focus on big blue octopus (Octopus cyanea), which is a widely found cephalopod species in the WIO, we compared landed catches (biomass, catch rate, and density) in submerged and exposed reefs, and explored the influence of proximity to fishing villages and reef habitat size on octopus landings. We used fishery-dependent data collected between 2018 and 2020 from eight landing sites spread across the Tanzanian coast. We found a strong relationship between biomass of octopus catch and distance from fished reefs to fishing villages, with higher fished biomass on reefs farther away. Octopus densities were higher, while catch rates were lower, on reefs very close to (within one km distance from) fishing villages compared to more distant reefs. In general, submerged reefs provided higher catches than exposed reefs. The low octopus catches on the exposed reefs were attributed to high fishing pressure, while submerged reefs that are only accessible through diving provide optimal areas for octopuses to grow. Octopus catches were, however, not significantly affected by reef size. The findings suggest that management policies should proportionate fishing efforts to ensure sustainable exploitation of reefs and associated fishery resources. [ABSTRACT FROM AUTHOR]