Reconstructing past fisheries catches for large pelagic species in the Indian Ocean

Abstract

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.

Uncovering the Effects of the Southwest Monsoon on Fishing Activity in the Indian Ocean with VIIRS Boat Detection Data

“…Fishery agencies have the potential to depend on VIIRS boat detection (VBD) data to enforce regulations and implement management measures effectively. VBD data can offer real-time insights into the actions of fishing vessels, including signs of unlawful fishing practices within restricted zones and intrusions into exclusive economic zones (EEZs) [7]. Figure 1 shows the percent frequency of VBD detection in the northern Indian Ocean.…”

Small-scale fisheries catch and fishing effort in the Socotra Archipelago (Yemen) between 1950 and 2019

“…The catch time series reconstructed here were assessed with respect to their data and data source reliability using the method applied in all maritime countries globally by as described in Pauly and Zeller (2017) and Heidrich et al (2023). This approach represents a form of uncertainty assessment, using the scoring system summarized in Supp.…”

Multiple Lines of Evidence Highlight the Dire Straits of Yellowfin Tuna in the Indian Ocean

“…They are characterized by rapid growth and high reproductive output (Murua et al, 2017), generally making such species relatively resistant to fisheries exploitation. The seven principal market tuna species, yellowfin (Thunnus albacares), skipjack (Katsuwonus pelamis), bigeye (Thunnus obesus), albacore (Thunnus alalunga), southern bluefin (Thunnus maccoyii), Atlantic bluefin (Thunnus thynnus), and Pacific bluefin tuna (Thunnus orientalis) are exploited globally, by small-scale (e. g., Okemwa et al, 2023) and large-scale industrial fisheries (Heidrich et al, 2023) in both developing and developed countries (FAO, 2020). Global tuna fisheries reached an estimated total catch of 4.9 million tonnes in 2020 (ISSF, 2022) contributing more than $40 billion to the global economy yearly (McKinney et al, 2020).…”