No information is available on the stock structure of longtail tuna in the Indian Ocean. The IOTC coordinated Stock Structure Project, which commenced in early-2015, aims to supplement gaps in the existing knowledge on biological data, and in particular provide an insight on whether neritic tuna and tuna like species should be considered as a single Indian Ocean stock.

No new assessment was conducted for longtail tuna in 2021 and so the results are based on the assessment carried out in 2020 using the Optimised Catch-Only Method (OCOM). Analysis using the OCOM indicates that the stock is being exploited at a rate that exceeded FMSY in recent years and that the stock appears to be below BMSY and above FMSY (76% of plausible models runs) (Fig. 2). Catches were above MSY between 2010 and 2018 but steadily declined from 2012 to were less than 113,000 t in 2019, below the estimated MSY (Fig. 1). The F2018/FMSY ratio is slightly higher than previous estimates. The estimate of the B2018 /BMSY ratio (0.69) was lower than in previous years, reflecting declining abundance. An assessment using a biomass dynamic model incorporating gillnet CPUE indices was also undertaken in 2020 and results were consistent with OCOM in terms of status. Therefore, based on the weight-of-evidence currently available, the stock is considered to be both overfished and subject to overfishing (Table 1; Fig. 2).