Title:

Using mechanistic models to assess temporary closure strategies for small scale fisheries

Mechanistic models are particularly useful for understanding and predicting population dynamics in data deficient species. Data deficiency is a relevant issue in small scale fisheries as they are generally under studied and underrepresented in global fishing datasets. As overfishing remains a global issue, especially in small-scale fisheries, one commonly utilized conservation method is temporary closures. The Octopus cyanea (blue octopus) fishery off the southwest coast of Madagascar is one such system that utilizes these closures, yet lacks sufficient data collection specific to this species to assess the viability of the population. This fishery is a key economic resource for the local community as blue octopus catch is sold by local fishers to international export markets and is a major component of fisher income. To assess the sustainability of blue octopus, we parameterize a Levkovitch population matrix model using existing catch data. In this study, we show that this population was in a decline of 1.8% per month at the time of data collection. We also assessed the effects of different temporary closures and which of these management strategies would result in a sustainable population of blue octopus. To sustain the existing population of blue octopus, our model indicates that the fishery would need to close at least once every five months for one month. Increasing the frequencies of closure are predicted to significantly increase the octopus population at these sites. We show that if implemented correctly, temporary closures could be utilized to restore this population. Since this data was collected, the local communities of Madagascar have implemented various fishing restrictions to ensure sustainable fishing, indicating a need for further research into the effectiveness of these fishing closures. Therefore, our study provides insight into the underlying population dynamics of this fishery and provides survivability estimates of this species.

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