DataSheet_1_Reconstructing past fisheries catches for large pelagic species in the Indian Ocean.docx

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.

全面捕捞数据对于支持大型远洋渔业资源的可持续管理至关重要。然而，印度洋金枪鱼委员会（IOTC）代表其成员国报告的捕捞数据目前未能充分反映印度洋这些渔业的规模。我们重建了1950年至2020年印度洋大型远洋物种的渔业捕捞量，旨在提高现有报告数据的完整性，并为研究和管理工作提供更具生态相关性的数据集。我们对在大型远洋渔业中运营的42个国家的五种主要渔具组（延绳钓、围网、刺网、钓具和其他渔具）进行了捕捞量重建。重建的捕捞量比IOTC报告的数据高出30%。我们证明了历史上以远程渔业船队为主导的大规模工业捕捞逐渐被悬挂印度洋沿岸国家国旗的船队所取代。我们的研究结果还表明，在1950年至2020年期间，平均弃鱼率约为14%，这主要归因于与延绳钓和刺网船队相关的广泛弃鱼实践。随着时间的推移，关于金枪鱼的报告有所改善，而鲨鱼的捕捞量仍然报告不足，在2020年占未报告总捕捞和弃鱼量的51%。我们确认，印度洋金枪鱼委员会代表其成员国报告的数据中存在大量分类聚团，这掩盖了重要的模式和趋势，并进一步复杂化了印度洋受捕捞物种的可持续管理。我们建议大幅增加观察员覆盖率，并要求所有成员国提供更全面、更强的支持，以改善IOTC的渔业统计数据。