Accounting for variability in life-history traits for the definition of amphidromous goby fry fisheries closure periods

Amphidromous goby fry (post-larvae and young juveniles) are traditionally fished when they arrive in rivers after their larval development at sea. In Reunion Island (Indian Ocean) two species of amphidromous goby are mainly targeted by the fisheries: the endemic Cotylopus acutipinnis and the cosmopolitan Sicyopterus lagocephalus. Despite the lack of quantitative data on these fisheries, their impact on populations is expected to be important because the catches can represent several tonnes per year. Consequently, fishery regulation changes have been proposed that increase the duration of the existing fisheries closure period of two weeks in March. We developed an approach to identify key periods for fisheries closure, including assessment of the proposed management scenario and several alternative protection scenarios, based on the maximization of fry abundance and on the variability of four life-history traits: (i) fry size and (ii) age at arrival in rivers, (iii) the time the juveniles spend in river before maturation and (iv) their migration behaviour. This approach is in seeking to preserve a high level of phenotypic diversity, which is predicted to promote population resilience. We conducted a multiple-criteria decision analysis to rank 4096 alternatives of fisheries closure periods, ranging from zero to 12 months, based on their propensity to maintain fry abundance and life history trait diversity. Finally, according to the type of fisheries closure period (discontinuous or continuous) and the proportion of annual abundance and variability of life-history traits preserved during the period (50% or 75%), we propose four different fisheries closures lasting from six to nine months.