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Of the twelve species of billfish, there are six species of Billfish in the Indian Ocean.
The term billfish refers to the large fishes of the family Istiophoridae, comprising marlin and sailfish, and of the family Xiphiidae, comprising swordfish. [1] Billfish are epipelagic and highly migratory fishes [2] [3] found throughout the world's oceans, typically inhabiting the coastal and offshore waters of tropical and temperate oceans. They are normally found in the upper 200 metres of water layers above the thermocline but may occur in depths up to 800 metres. They migrate into temperate or cold waters for feeding and back to tropical waters for spawning. [1]
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] All billfish species are sexually dimorphic with the females attaining larger sizes than males. Spawning occurs in tropical waters with eggs hatching into larvae which feed on planktons.
Billfishes are active and voracious apex predators using their long bill to attack and stun their prey by moving their heads in a sideways motion, knocking their prey unconscious and making it easier to catch. They feed on a wide variety of tuna-like fishes, cephalopods and crustaceans. [1]
Of the twelve species of billfish, the following six species [1] are found in the Indian Ocean which comprises the FAO major fishing areas 51 (Western Indian Ocean) and 57 (Eastern Indian Ocean).
| Family | Genus | Common name | Scientific name | Maximum length | Maximum weight | Fishbase |
| Istiophoridae | Makaira | Black marlin | Makaira indica (Cuvier, 1832) | > 448 cm | 700 kg | [4] |
| Indo-Pacific blue marlin | Makaira mazara (Jordan & Snyder, 1901) | 450 cm | 900 kg | [5] | ||
| Tetrapturus | Striped marlin | Tetrapturus audax (Philippi, 1887) | 350 cm | 200 kg | [6] | |
| Shortbill spearfish | Tetrapturus angustirostris (Tanaka, 1915) | 200 cm | 52 kg | [7] | ||
| Istiophorus | Indo-Pacific sailfish | Istiophorus platypterus (Shaw, 1792) | 340 cm | 100 kg | [8] | |
| Xiphiidae | Xiphias | Swordfish | Xiphias gladius (Linnaeus, 1758) | 455 cm | 540 kg | [9] |
These six billfish species are not usually targeted by industrial and artisanal fisheries operating throughout the Indian Ocean but are caught and retained as a by-product. These species are important for localised small-scale and artisanal fisheries and recreational fishing.
Black marlin (Makaira indica) inhabits the tropical and subtropical waters of the Indian Ocean between latitudes 25o N and 45o S. [1] M indica is largely considered to be a bycatch of industrial and artisanal fisheries and since the 1990s catches in the Indian Ocean have increased steadily, from 2,800 t in 1991 to over 10,000 t in 2004. In recent years catches have further increased sharply from around 15,000 t in 2013 to over 22,000 t in 2016 and 2017. [10] Gillnets account for around 50% of total catches, followed by longlines (17%), with remaining catches by troll and handlines. Based on 2013-2017 catches, the main fleets are operated by India (27%), Iran (26%), Sri Lanka (18%) and Indonesia (14%). [10]
The Indo-Pacific blue marlin (Makaira mazara) is found primarily in tropical and subtropical waters of the Indian Ocean between latitudes 25o N and 40o to 45°S of the southwestern region and 35°S in the southeastern region. [1]
M mazara is largely a non-target specie of industrial and artisanal fisheries. Western Indian Ocean is the main fishing area operated by longliners which account for 70% of total catches followed by gillnets (24%) with remaining catches by troll and handlines. Catches until the late 1970s were around 3,000 t to 4,000 t and steadily increased to over 10,000 t by the early 1990s and over 17,000 t by 2016. The main fleets, based on 2013-2017 catches, are operated by Taiwan,China (34%), Indonesia (31%), Pakistan (12%), Iran (9%) and Sri Lanka (6%). [10]
Striped marlin (Tetrapturus audax) is found in the Indian Ocean mainly in the tropical, subtropical and temperate waters between latitudes 25o N and as far south as 45°S in the southwestern region and 35°S in the southeastern region. [1] T audax is considered to be a non-target specie of industrial fisheries with catch trends ranging from 2000 t to 8000 t per year. Most of the catch is taken in the north-west Indian Ocean, although catches dropped markedly between 2007 and 2011 due to piracy. Based on 2013-2017 catches, longlines account for around 66% of total catches followed by gillnets (27%). These catches were operated by fleets from Indonesia (37%), Taiwan, China (19%), Iran (16%) and Pakistan (8%). [10]
Shortbill spearfish (Tetrapturus angustirostris) is an oceanic pelagic fish which does not generally occur in coastal or enclosed waters but is found well offshore. It is found between latitudes 20°N and 35°- 45°S in the Indian Ocean. [1]
The Indo-Pacific sailfish (Istiophorus platypterus) is usually found above the thermocline between latitudes 20°N and 45°S in the western Indian Ocean and 35°S in the eastern Indian Ocean. [1] The main fishing area is the north-west Indian Ocean around the Arabian Sea. Catches increased sharply from around 5,000 t in the mid-1990s to nearly 30,000 t as from 2011 with the development fisheries in Sri Lanka and Iran. [10]
The Swordfish (Xiphias gladius) is a large oceanic apex predator inhabiting all the world's oceans. It is found in the entire Indian Ocean down to latitude 45°S. [1] Before the 1990s X gladius was mainly a non-targeted catch of industrial longline fisheries; but after 1990 catches increased from around 8,000 t to 36,000 t in 1998 with longliner fleets changing their targets from tunas to swordfish. Annual catches decreased during the mid 2000s in response to the piracy threat in the area off Somalia but have improved since 2012 with the control of the threat. [10]
Commercial fishing in the Indian Ocean started in the early 1950s with Japanese fishing yellowfin and bigeye tuna using longlines and they were followed in the late 1960s by fishing fleet from Taiwan, China and The Republic of Korea. [2] Since 1980 European fleet from Spain, Portugal, France and UK started fishing tuna in the Indian Ocean using purse seine. [11] Up to the early 1980s over 90% of billfishes were taken as incidental bycatch by long line vessels. This has decreased to between 50% and 70% during the past 20 years as billfish catches from offshore gillnet fisheries have become more important for fleets from Iran and Sri Lanka. [10]
Total billfish catch which averaged 10,000Mt in the 1960s and 1970s increased to 75,000Mt by the 2000s. The average catch for 2013-2017 was 113,000Mt with swordfish and Indo-Pacific sailfish accounting for around two thirds of total catches followed by black marlin, blue marlin and striped marlin. [10] In the last few years, 75% of all billfish catches were recorded by five countries comprising Indonesia, Iran, India, Sri Lanka and Taiwan, China. [10] 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. [10]
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. Main sport fisheries are located in West Australia, Kenya, Mauritius, La Reunion Island, Seychelles and South Africa. [12]
Sports fishermen go on private fishing boats and while at sea, they tend to follow school of seagulls, as these birds usually dive-hunt for small surface fish. Live baits such as bonitos are used as well as plastic lures mirroring the effects of swimming squids. The fishing trip can take hours usually ending around midday.
Tag and release is commonly used, as it positively impacts conservation and provides important information for the study of the species. There has been over 55,000 recorded tags in East African Indian Ocean waters, mainly compromising of sailfish and marlins. [12]
Global assessment of the status of billfish indicate the most of the stocks are experiencing high mortality rates with some species being overfished. [13] For the last two decades Indian Ocean billfish stocks have been subject to particularly intense fisheries pressure 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. [10] The declining billfish stocks is as a result of the growing demand for their meat in the global market as well as for artisanal fisheries primarily in Sri Lanka and Indonesia. [13]
A reduction in fishing pressure was noted in the 2000s attributed to the threats from pirates operating around the horn of Africa off the coast of Somalia. However, with the reduced threat of piracy in recent years, pressure on billfish stocks appears to be increasing again. [13]
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. [14] > 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. [14]
Regional Fisheries Management Organisations (RFMOs) were established to manage and conserve tuna and billfish stocks due to their transnational distributions and widespread economic importance. The billfish population which is exploited or taken as bycatch by multinational fisheries is becoming difficult to regulate due to the non availability of accurate catch data which may not be collected or is aggregated with other species.
The Indian Ocean Tuna Commission (IOTC) was established as an intergovernmental RFMO in 1993 within the framework of the Food and Agriculture Organisation (FAO) of the United Nations for the management of tunas and tuna like species in the Indian Ocean and adjacent seas under the “Agreement for the Establishment of the Indian Ocean Tuna Commission”. The principal objective of the IOTC as stated in Article V, para 1 is to ensure “…. through appropriate management, the conservation and optimum utilization of stocks covered by this Agreement and encouraging sustainable development of fisheries based on such stocks.”
Under this mandate the IOTC reviews the conditions and trends of tuna and billfishes stocks in the Indian Ocean, performs research on these stocks and adopts conservation and management measures. [15]
Membership of the IOTC is open to coastal states of the Indian Ocean or states whose vessels engage in fishing in the Indian Ocean for stocks covered by the Agreement. There are presently 33 states who are members of the IOTC. [15]
With the exception of swordfish, which is a target of commercial fisheries, the status of the other species of billfishes in the Indian Ocean is uncertain with their assessment and management becoming complicated and at times ineffective. [15]
The billfish assessment carried out by the IOTC in 2017 established that the swordfish stock was not overfished and not subject to overfishing. The other four billfish species (black marlin, blue marlin, striped marlin and Indo-Pacific marlin) were either overfished or have been experiencing overfishing. [10]
At its 22nd session held on 21–25 May 2018 the IOTC adopted Resolution 18/05 “On Management Measures for the conservation of the Billfishes: Striped Marlin, Black Marlin, Blue Marlin And Indo-Pacific Sailfish”. [16] The Resolution set catch limits for these four billfishes in order not to exceed their Maximum Sustainable Yield (MSY). The IOTC will review the catch levels and would consider implementing additional conservation and management measures in the event that the catch levels were to exceed the set limits in any two consecutive years as from 2020 onwards.
As a result of the declining billfish population sport fishermen and conservationists have established tag and release program that tag, release and report the billfish catches. The use of tags and data gathered from recaptured billfish provides valuable scientific data on their growth rates, migratory patterns and stock assessment. The African Billfish Foundation was established in 1991 as a nonprofit organisation for conservation and research of the billfish species in the Indian Ocean. It has an active tag and release program with an excess of 55,000 fish tagged. Additionally, the government of Seychelles is encouraging the use of small-scale fisheries in order to sustain the continuous increasing demand for ocean products
Although having strong measures and awareness campaigns, the billfish population is still under threat, with the blue marlin classified as vulnerable by the IUCN Red List. [17]
Marlins are fish from the family Istiophoridae, which includes about 10 species.
The swordfish, also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood. These fish are found widely in tropical and temperate parts of the Atlantic, Pacific, and Indian Oceans, and can typically be found from near the surface to a depth of 550 m (1,800 ft), and exceptionally up to depths of 2,234 m. They commonly reach 3 m (10 ft) in length, and the maximum reported is 4.55 m in length and 650 kg (1,430 lb) in weight.
The albacore, known also as the longfin tuna, is a species of tuna of the order Scombriformes. It is found in temperate and tropical waters across the globe in the epipelagic and mesopelagic zones. There are six distinct stocks known globally in the Atlantic, Pacific, and Indian oceans, as well as the Mediterranean Sea. The albacore has an elongate, fusiform body with a conical snout, large eyes, and remarkably long pectoral fins. Its body is a deep blue dorsally and shades of silvery white ventrally. Individuals can reach up to 1.4 m in length.
Longline fishing, or longlining, is a commercial fishing angling technique that uses a long main line with baited hooks attached at intervals via short branch lines called snoods or gangions. A snood is attached to the main line using a clip or swivel, with the hook at the other end. Longlines are classified mainly by where they are placed in the water column. This can be at the surface or at the bottom. Lines can also be set by means of an anchor, or left to drift. Hundreds or even thousands of baited hooks can hang from a single line. This can lead to many deaths of different marine species. Longliners – fishing vessels rigged for longlining – commonly target swordfish, tuna, halibut, sablefish and many other species.
Big-game fishing, also known as offshore sportfishing, offshore gamefishing or blue-water fishing, is a form of recreational fishing targeting large game fish, usually on a large body of water such as a sea or ocean.
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.
The white marlin, also known as Atlantic white marlin, marlin, skilligalee, is a species of billfish that lives in the epipelagic zone of the tropical and subtropical Atlantic Ocean. They are found between the latitudes of 45° N and 45° S in waters deeper than 100 m. Even though white marlin are found in bodies of water that are deeper than 100 m they tend to stay near the surface. White marlin have been found near banks, shoals, and canyons, but they are not limited to those locations. They prefer warm surface temperatures greater than 22 °C.
The Atlantic blue marlin is a species of marlin endemic to the Atlantic Ocean. It is closely related to, and usually considered conspecific with, the Indo-Pacific blue marlin, then simply called blue marlin. Some authorities consider both species distinct.
Fish stocks are subpopulations of a particular species of fish, for which intrinsic parameters are traditionally regarded as the significant factors determining the stock's population dynamics, while extrinsic factors are traditionally ignored.
The International Commission for the Conservation of Atlantic Tunas (ICCAT) is a tuna regional fishery management organisation, responsible for the management and conservation of tuna and tuna-like species in the Atlantic Ocean and adjacent seas. The organization was established in 1966, at a conference in Rio de Janeiro, Brazil, and operates in English, French and Spanish. The organisation has been strongly criticised by scientists for its repeated failure to conserve the sustainability of the tuna fishery by consistently supporting over-fishing – an internal review branded ICCAT's policies on the eastern Atlantic bluefin tuna fishery a "travesty of fisheries management", and an "international disgrace". Conservationists often refer to ICCAT as "The International Conspiracy to Catch All Tuna".
The billfish are a group of saltwater predatory fish characterised by prominent pointed bills (rostra), and by their large size; some are longer than 4 m (13 ft). Extant billfish include sailfish and marlin, which make up the family Istiophoridae; and swordfish, sole member of the family Xiphiidae. They are often apex predators which feed on a wide variety of smaller fish, crustaceans and cephalopods. These two families are sometimes classified as belonging to the order Istiophoriformes, a group which originated around 71 million years ago in the Late Cretaceous, with the two families diverging around 15 million years ago in the Late Miocene. However, they are also classified as being closely related to the mackerels and tuna within the suborder Scombroidei of the order Perciformes. However, the 5th edition of the Fishes of the World does recognise the Istiophoriformes as a valid order, albeit including the Sphyraenidae, the barracudas.
The black marlin is a species of marlin found in tropical and subtropical areas of the Indian and Pacific Oceans. Reaching lengths of over 4.5 m (15 ft), it is one of the largest marlins and also one of the largest bony fish. Marlin are among the fastest fish, but speeds may be exaggerated in popular media, such as reports of 132 km/h (82 mph). A 2016 study estimated maximum swimming speeds from muscle contraction times, which in turn limit the tail-beat frequency; the study suggested a theoretical upper limit for the black marlin's burst speed of 36 kilometres per hour (22 mph). Black marlin are fished commercially and are also a highly prized game fish. Black marlins have been known to drag Maldivian fishing boats of the ancient times for very long distances until it got tired; and then it would take many hours for the fishermen to row or sail back home.
The striped marlin is a species of marlin found globally in tropical to temperate oceans not far from the surface. It is a desirable commercial and game fish, although conservation measures are in place to restrict its commercial landings. An epipelagic predator, it hunts during the day in the top 100 metres (330 ft) or so of the water column, often near the surface. One of its chief prey is sardines.
The bigeye tuna is a species of true tuna of the genus Thunnus, belonging to the wider mackerel family Scombridae. In Hawaiian, it is one of two species known as ʻahi, the other being the yellowfin tuna. Bigeye tuna are found in the open waters of all tropical and temperate oceans, but not in the Mediterranean Sea.
Marlin fishing or billfishing is offshore saltwater game fishing targeting several species of fast-swimming pelagic predatory fish with elongated rostrum collectively known as billfish, which include those from the families Istiophoridae and Xiphiidae (swordfish). It is considered by some fishermen to be a pinnacle of big-game fishing, due to the size, speed and power of the billfish and their relative elusiveness.
National Coalition for Marine Conservation is now operating as "Wild Oceans." Founded in 1973 by fishermen, the National Coalition for Marine Conservation (NCMC) is the United States's oldest public advocacy group dedicated exclusively to conserving ocean fish and their environment. The NCMC's mission is to build awareness of the threats to USA marine fisheries and convince policy-makers to restore and protect publicly owned fishery resources. Its efforts focus on stopping overfishing, reducing bykill caused by indiscriminate fishing gear, and stemming the loss of critical marine habitat.
The roundscale spearfish is an Istiophoridae species of marlin living in the epipelagic zone of the Atlantic Ocean. It has long been misidentified as white marlin but can be differentiated thanks to their scale shapes that gives its name. Not much is known about this species. It could reach a length of 160 cm and 21,5 kg and has no conservation status yet due to a lack of data.
Land-based game fishing is a form of big-game sport fishing in which anglers attempt to catch oceanic game fish from shore rather than from ocean-going boats. The locations for such activities are generally rock platforms, though wharfs, jetties and beaches are also common. Some species such as sharks can be targeted in shallow littoral water, however most other species prefer deeper pelagic water, and this limits the areas where these types can be fished from the shore. Tackle used is usually comparable to that used on boats, but some differences are necessary, such as changes in rod length. Different tackle is used according to location and species targeted.
As with other countries, the 200 nautical miles (370 km) exclusive economic zone (EEZ) off the coast of the United States gives its fishing industry special fishing rights. It covers 11.4 million square kilometres, which is the second largest zone in the world, exceeding the land area of the United States.
The Indo-Pacific blue marlin is a species of marlin belonging to the family Istiophoridae.