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Comprehensive catch data are fundamental to support the sustainable
management of large pelagic fisheries. However, catch data reported by the
Indian Ocean Tuna Commission (IOTC) on behalf of its member countries
currently under-represent the extent of these fisheries in the Indian Ocean. We
reconstructed fisheries catches of large pelagic species for the Indian Ocean
from 1950 to 2020, aiming to improve the comprehensiveness of existing
reported data and to provide more ecologically relevant datasets for research
and management uses. We reconstructed catches for 42 countries operating five
major gear groups (longline, purse seine, gillnet, pole-and-line, and other gears)
in the large pelagic fisheries. Reconstructed catches were 30% higher than the
data reported by the IOTC. We demonstrated that distant-water fishing fleets
historically dominated large-scale industrial fishing but were gradually replaced
by fleets flagged to Indian Ocean rim countries. Our results also indicated an
average discard rate of ~14% over the 1950-2020 period, primarily attributable to
extensive discarding practices associated with longline and gillnet vessels.
Reporting over time has improved only for tunas, whereas shark catches still
remain under-reported, accounting for 51% of total unreported landings and
discards in 2020. We confirmed substantial taxonomic aggregation in the data
reported by the IOTC on behalf of its member countries, masking important
patterns and trends and further complicating the sustainable management of
exploited species in the Indian Ocean. We recommend substantially increased
observer coverage and far better and stronger support by all member countries
to improve the fisheries statistics in the IOTC.
