Assessing the effectiveness of dFADs fishing moratorium in the Eastern Atlantic Ocean for conservation of juvenile tunas from AOTTP data

Targeting tunas associated with drifting Fish Aggregating Devices (dFADs) raises questions on the sustainability of tropical tuna fisheries. To limit catches of juvenile tunas, multiple time-area dFADs-fishing moratoria have been implemented by ICCAT since 1998. In this study we assessed the effectiveness of two different dFADs time-area closures implemented for the protection of both bigeye and yellowfin tuna juveniles. Using Atlantic Ocean Tunas Tagging Program (AOTTP) data from 2016 to 2019, we estimated the relative risk for individuals tagged inside the moratorium strata to be recaptured inside in comparison to the recapture rate outside the spatio-temporal strata. AOTTP releases were not homogeneously distributed in terms of areas and school type, therefore to assess the effect of the moratorium without potential bias a matching procedure was used to rebalance the release areas. As a result of the matching procedure and subsequent filtering applied to the dataset, the number of bigeyes recaptures retained inside and outside the time-area closure were below the threshold from which any conclusion could be drawn. In contrast, our results show that a majority of yellowfin and skipjack tunas tagged within the closed area stayed within the closed area during the moratorium period. Consequently, the last moratorium can be considered as effective for these two species, at least during the months of fishing ban on dFADs.