Standardized CPUE of swordfish (Xiphias gladius) from Indonesian tuna longline fleets in the north-eastern Indian Ocean

Swordfish (Xiphias gladius) is a large oceanic apex predator inhabits all the world’s oceans. It is predominantly known as a subject of exploitation worldwide, mainly in the Pacific Ocean, Atlantic Ocean, and Mediterranean Sea (Tserpes & Tsimenides, 1995). Throughout the Indian Ocean, swordfish are primarily caught by longline fisheries, and the commercial harvest was first recorded by the Japanese in the early 1950s as bycatch of their tuna longline fisheries (IOTC-WPB16, 2018). Since 1990s the catches of swordfish increased sharply to a peak of 35,000 tons in 1998 (IOTC-WPB16, 2018) due to the growing shift of catching tunas to swordfish by Taiwanese longline fleets, the increasing number of longline fleets operations from various nations (e.g. Indonesia, Australia, La Reunion, Seychelles and Mauritius), and arrival of longline fleets from the Atlantic Ocean (e.g. Portugal, Spain and United Kingdom).

In recent years (2013-2017), Indonesian fleets are responsible for approximately 20% of the total catch of swordfish in the Indian Ocean (~8,000 MT), followed by Taiwan (17%), Sri Lanka (12%) and Spain (12%) (IOTC-WPB16, 2018). However, the total catch was revised to just under ~3,000 MT (9%) due to the refined methodology on catch estimation provided by the IOTC secretariat (IOTC-WPDCS14, 2018). In addition, the revision also aligned with the impact of Ministerial Regulation No. 56/2014 and No. 57/2014 about the moratorium on foreign fishing vessels and prohibition of transshipment at sea within Indonesia national jurisdiction, which resulted in a significant reduction of longline vessel operations from 584 in 2015 to 271 in 2016.

Our analytical objective was to investigate how the data-limited of swordfish fishery can construct a fairly robust relative abundance indices amid the "spatial gap" of the existing dataset for standardized CPUE in the eastern Indian Ocean (e.g., Japanese and Taiwanese longline dataset). We believe the results are valuable as an important information to assess the status of swordfish in the Indian Ocean.