Indian Ocean Skipjack tuna stock assessment 1950-2022

This report summarises a stock assessment for Indian Ocean Skipjack tuna (Katsuwona pelamis) using Stock Synthesis 3 (SS3). The assessment assumed the Indian Ocean skipjack tuna constitute a single stock and is based on a spatially aggregated and seasonally structured model that integrates several sources of fisheries and biological data. The assessment model covers the period 1950–2022 and represents an update and revision of the 2020 assessment model with the inclusion of updated CPUE indices and length composition data. Standardised CPUE series from Maldives Pole and line fleet 1995 – 2022 and EU associated Purse seine sets 1990 – 2021 were included in the models as relative abundance index of exploitable biomass. An additional index based on associative dynamics of skipjack tuna with floating objects was considered as an alternative index for the abundance trend for more recent years (2013–2022). Tag release and recovery data from the RTTP-IO program were included in the model to inform abundance and fishing mortality rates. Several sensitivity models are presented to explore the impact of key data sets and model assumptions