Seascape configuration influences big blue octopus (Octopus cyanea) catches: Implications for a sustainable fishery

Abstract

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.