Exploring complexities of fishery closures using octopus movements : an individual-based modelling approach

Temporary closures of octopus fishing areas constitute a promising co-management measure that aims to improve local governance, food security and incomes in coastal small-scale fishing communities. Although positive social and economic outcomes of temporary closures are increasingly reported, the underlying social-ecological and ecological interactions, and their impact on closure benefits are rarely studied. This lack of systemic understanding may lead to undesired outcomes. Here, I extend an existing agent-based model of temporary closures to explore the influence of individual octopus movements on ecological outcomes and fishers’ benefits in Zanzibar. First, I conceptualized the octopus closure system by analyzing empirical qualitative data and literature. Next, I iteratively developed and tested an individual-based model extension. This extension simulates between-den movements across a hypothetical seascape and formalizes intrinsic attributes of Octopus cyanea such as movement patterns and maturity stages. I analyzed the effects of varying closure size of fishing grounds temporarily closed to illustrate potential implications for outcomes of octopus closures. Simulation results show that individual octopus movements triggered by fishing activities have noticeable impacts on octopus sizes, their spatial and temporal distribution, and fishers’ catches, particularly when considering different social groups that depend on the fishery. Scenarios with closures in place show higher mean octopus weight in closed areas in contrast to open-access areas. Mean catches for women foot-fishers are lower compared to freedivers’ catches and even slightly lower when allowing octopuses to move in response to disturbance in all scenarios. Catch rates and distribution of mature octopuses are highly sensitive to closure size revealing a social-ecological trade-off when implementing larger closures. This study demonstrates an approach to integrating individual octopus movements and interactions between fishers and octopuses in a fishery management context, and suggests that reactive movement of octopus contributes to unequal distribution of the closure benefits between different social groups.Octopus and People In Novel Transdisciplinary Simulations (OctoPINTS project