Billfish resources of India with special reference to the fishery and biology of blue marlin Makaira nigricans caught from the Eastern Arabian Sea

Surya, S and Abdussamad, E M and Mini, K G and Santhosh, B and Rajesh, K M and Manas, H M and Abdul Azeez, P and Jeena, N S and Chellappan, Anulekshmi and Pradeep, H D and Vinothkumar, R and Muktha, M and Kizhakudan, Shoba Joe and George, Grinson (2025) Billfish resources of India with special reference to the fishery and biology of blue marlin Makaira nigricans caught from the Eastern Arabian Sea. In: Working Party on Billfish (WPB).

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Abstract

Billfish, comprising sailfishes, marlins, spearfishes, and swordfishes, are highly migratory and large pelagic predators distributed globally across tropical and subtropical oceans. Along the Indian coast, the estimated landings of billfishes have shown a rising trend, reaching 21,321 tonnes in 2024. The major species contributing to landings during 2009–2024 include Istiophorus platypterus (50%), Istiompax indica (23%), Makaira nigricans (12.5%), Xiphias gladius (15%), and Kajikia audax (<1%). Mechanized gillnetter cum hook-and-line units were the primary gears responsible for billfish capture. Molecular identification using cytochrome oxidase I (COI) gene barcoding successfully differentiated four billfish species occurring in Indian waters. Mitochondrial DNA control region (mtDNA-CR) based phylogenetic analysis revealed two well-supported sub-clades within the major clades I and II, further aiding in species-level differentiation. The reproductive and feeding biology of M. nigricans (blue marlin) was studied using 764 specimens (237 females, 364 males, and 163 unidentified) collected between 2017 and 2024, with lower jaw fork lengths (LJFL) ranging from 130 to 305 cm. Among females, 23.2% measured <200 cm LJFL, while 76.8% were >200 cm LJFL. In contrast, 61% of males were <200 cm LJFL and 39% were >200 cm LJFL. The length at first maturity (Lm50) was estimated at 185 cm LJFL for females and 179.56 cm LJFL for males. Gonadosomatic index (GSI) values ranged from 0.6 to 3.9 in females and 0.6 to 3.1 in males, with peak values observed in May, indicating peak spawning during the pre-monsoon and monsoon months (April–June). Oocytes within the size range of 0.2–0.9 mm were included in fecundity estimations, which ranged from 1.67 to 11.1 million eggs. The spatial distribution of billfish resources from 2018-2023 collected by the Fishery Survey of India, Tuna Longline survey vessels MFV YellowFin and MFV Matsya Vrushti along the Indian EEZ of Arabian sea reveals that the spatial distribution of billfish hooking rates (0.01–2.0) in the Arabian Sea within India’s EEZ off the west coast, showing low to moderate rates (0.01–1.12) across most areas and distinct high-intensity hotspots (1.12–2.0) southwest of the mainland near the Lakshadweep Islands. Histological evidence also confirmed that the eastern Arabian Sea, particularly the Lakshadweep region, serves as a significant spawning ground for blue marlin, with the presence of mature and spent females. The feeding strategy estimated from the diet matrix revealed the BUM as a specialist predator that feeds on specific prey species or groups of individuals specialised on selective prey types.

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