The yellowfin tuna stock in the Indian Ocean is in poor condition. Although fishing pressure has decreased in recent years, the stock is still heavily overfished. Current fishing mortality and catches remain well above the level associated with maximum sustainable yield (MSY), while the spawning stock biomass is only 31% of its original level.
The purse seine fishery can be directly linked to threats to several ETP species, including rays and sharks, which are subsequently discarded. Although the mortality rate of these species is estimated at only 1–5%, bycatch and discards are believed to be substantially underreported. There are also indications that the fishery disrupts the functioning of the local ecosystem, both indirectly through the bycatch of non-target species and directly through the removal of tuna itself. The risk of lost fishing gear is also among the highest of the fishing methods assessed. However, purse seines have relatively low carbon emissions, and their impact on the seabed is negligible because the nets do not come into contact with the benthos.
The management of yellowfin tuna in the Indian Ocean falls under the responsibility of the Indian Ocean Tuna Commission (IOTC). Data are collected for commercially valuable species such as yellowfin tuna, which is caught in large quantities by industrial fleets, but there is considerable uncertainty about the reliability of these data.
Measures to combat illegal and unreported fishing and to protect ETP species and the local ecosystem are largely ineffective due to weak enforcement and poor compliance. Sample-based estimates indicate that catches may be around 30% higher than those reported to the IOTC, while compliance with regulations and catch targets has declined in recent years.