User:Rolofrolo/sandbox
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Thanks!Billfish in the Indian Ocean
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Species
[edit]The term billfish refers to the large fishes of the Istiophoridae family comprising marlin and sailfish and the Xiphiidae family comprising swordfish. They are “characterized by the prolongation of the upper jaw, much beyond the lower jaw into a long rostrum which is flat and swordlike (swordfish) or rounded and spearlike (sailfishes, spearfishes and marlins).[1] Billfish are pelagic fishes inhabiting the coastal and offshore waters of tropical and temperate oceans. They migrate into temperate waters for feeding and back to tropical waters for spawning. Billfishes are active and voracious predators using their long bill to attack and stun their prey.
Of the 12 species of billfish the following 6 species are found in the Indian Ocean[2].
| Family | Genus | Common name | Scientific name | Maximum length | Maximum weight |
| Istiophoridae | Makaira | Black marlin | Makaira indica (Cuvier, 1832) | > 448 cm | 700 kg |
| Indo-Pacific blue marlin | Makaira mazara (Jordan & Snyder, 1901) | 450 cm | 900 kg | ||
| Tetrapturus | Striped marlin | Tetrapturus audax (Philippi, 1887) | 350 cm | 200 kg | |
| Shortbill spearfish | Tetrapturus angustirostris (Tanaka, 1915) | 200 cm | 52 kg | ||
| Istiophorus | Indo-Pacific sailfish | Istiophorus platypterus (Shaw, 1792) | 340 cm | 100 kg | |
| Xiphiidae | Xiphias | Swordfish | Xiphias gladius (Linnaeus, 1758) | 455 cm | 540 kg |
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Fishing of Billfish in the Indian Ocean
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Commercial fishing
[edit]Commercial fishing in the Indian Ocean started in the early 1950s with Japanese fishing yellowfin and bigeye tuna and they were followed by Taiwan Province of China and The Republic of Korea in the late 1960s[3]. Most billfishes were then taken as incidental bycatch by trawlers fishing for tuna using drift nets and long lines[4].
Total billfish catch averaged 10,000Mt in the 1960s and 1970s and increased to 75,000Mt by the 2000s. Longline fleets were responsible for over 90% of total billfish catches up to the early 1980s although billfishes were non targeted catch. However, in the past 20 years, the share by longline decreased to 50% to 70% of all billfish catches with increases in catches from offshore gillnet fisheries from Iran and Sri Lanka[5]. The average catch for 2013-2017 was 113,000 Mt with Indo-Pacific sailfish and swordfish accounting for around two thirds of total catches[5]. In the last few years, 75% of all billfish catches in the Indian Ocean were recorded by five countries comprising Iran, Indonesia, India, Sri Lanka, Taiwan and China[5].
The methods used for commercial fishing of billfish vary greatly by country with Indonesia, Taiwan, China and Spain having mainly longline fleets whereas Iran and Pakistan primarily use gillnets[5].
Recreational fishing
[edit]Billfish are amongst the most prized fish in recreational fishing in the Indian Ocean, along with Dorados and Tunas. Sport fisheries mainly target Indo-Pacific sailfish, black and blue marlins.
Sports fishermen usually go out at sea early in the morning on private fishing boats. While at sea, they tend to follow schools of seagulls, as these birds usually dive-hunt for small surface fish. Fishing enthusiasts are often after the larger predatory fish hunting from down below. Live baits are used such as bonitos as well as plastic lures, mirroring the effects of swimming squids. The fishing trip can take hours usually ending around midday.
Sport fisheries are located in India, Indonesia, Madagascar, Mauritius, La Reunion Island, Seychelles, Thailand, Sri Lanka, Australia, Tanzania, United Arab Emirates and Oman[5].
Tag and release is commonly used, as it positively impacts conservation and provides important information for the study of the specie. There has been over 55,000 recorded tags in East African Indian Ocean waters, mainly compromising of sailfish and marlins[6].
Threats
[edit]For the last two decades Indian Ocean billfish stocks have been subject to particularly intense fisheries pressures as a result of the increase in longline vessels up to the early 1980s which accounted for over 90% of the total billfish non-targeted catch. Presently all stocks have either been overfished or have been experiencing overfishing with swordfish being the exception[4]. A reduction in fishing pressure was noted in the 2000s attributed to the threats from pirates operating around the horn of Africa (primarily Somalia). However, with the reduced threat of piracy in recent years, pressure on billfish stocks appears to be increasing again[4].
The rapid warming over the western Indian Ocean noted during the past six decades has led to a decrease of up to 20% in phytoplankton in this region[7]. The reduction in phytoplankton may add further pressure on the fish stock levels including billfish with the risk of decline to a point of no return[7].
Conservation
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References
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- ^ Izumi, Nakamura (1985). "Billfishes of the World. An annotated and illustrated catalogue of Marlins, Sailfishes, Spearfishes and Swordfishes Known to date". FAO Fisheries Synopsis.
- ^ "Report of the 16th Session of the IOTC Working Party on Billfish". Indian Ocean Tuna Commission, IOTC–2018–WPB16–R[E]. September 2018.
- ^ Miyake, M.P (2004). "Historical trends of tuna catches in the world". FAO Fisheries Technical Paper – via FAO.
- ^ a b c Sharma, R. (2018). "Factors related to the decline and rebuilding of billfish stocks in the Atlantic and Indian oceans". ICES Journal of Marine Science.
- ^ a b c d e "Review of the statistical data and fishery trends for billfish". Indian Ocean Tuna Commission. 23 August 2018.
- ^ "Acquisition of catch-and-effort and size data from sport fisheries in the Western Indian Ocean". Indian Ocean Tuna Commission. October 2017.
- ^ a b Roxy, M. K (2016). "A reduction in marine primary poductivity driven by rapid warming over the tropical Indian Ocean". Geophys.