A.E. Caton
Bureau of Resource Sciences
PO Box E11, Queen Victoria Terrace
PARKES A.C.T. 2600, Australia
ABSTRACT
This report identifies, and provides a qualitative description of, the commercial and recreational components of the global southern bluefin tuna fisheries. It describes their distribution in time and space and includes details of catch magnitude and age composition.
1. INTRODUCTION
The study of interactions among components of the global fishery for southern bluefin tuna (SBT; Thunnus maccoyii) in the first instance requires the identification of those components, their distribution in time and space, and their relative significance. This summary provides a qualitative description, augmented by generalized indications of catch magnitude and size composition. Comprehensive time series of SBT catch data for commercial vessels from Australia, Japan and New Zealand are available but the data for catches by other countries, and for recreational fisheries, are much less certain.
2. COMMERCIAL FISHERIES
The major commercial fisheries for SBT have been the Australian surface fishery (predominantly purse-seine and pole-and-line) for juveniles, the Japanese longline fishery for older juveniles and adults, an expanding Taiwanese longline fishery and, on a smaller scale, New Zealand's surface and longline fisheries (Caton, 1991). Less substantial commercial activities are, or have been, carried out by longliners from Indonesia and Korea, and there is a bycatch of SBT in the Taiwanese gillnet fishery.
2.1 Australia
2.1.1 Western Australian pole-and-line fishery
A pole-and-line fishery with SBT as the target species, locating fish by trolling and using dead pilchards (Sardinops neopilchardus) as chum, was located year-round along the western south coast of Western Australia (Figure 1). It commenced at the end of the 1960s, the catch steadily increasing to 6,000 mt in 1982/83 (representing some 1.2 million fish), then rapidly declining as a result of quota regulations. The annual catch is now less than 20 mt (4,000 fish). The catch was used almost exclusively for canning, then there was an emphasis on exporting fresh fish to the Japanese sashimi market, but the main use remaining is for local processing as smoked tuna. The fleet, which exceeded 100 vessels at the peak of activity, currently consists of three or four vessels fishing for SBT on a part-time basis. Average length of fish in the catch has usually been about 65 cm (5 kg; 2 1/2 years old), the main age classes taken being 1–3 year olds.
Figure 1. Southern bluefin tuna spawning ground and migration pattern within and out of Australian waters. The 200-mile Australian fishing zone is indicated by the solid line and the horizontal hatching indicates the composite distribution of the Australian surface fishery. The general distribution of Japanese longline fishing is inset. (Modified from Majkowski et al., 1988).
A very small amount of skipjack tuna (Katsuwonus pelamis), albacore (Thunnus alalunga) and bigeye (T. obesus) were taken incidentally. The only other pelagic fishery in the region, and one in which some of the multi-purpose SBT vessels operated, is a small-vessel, purse-seine fishery for pilchards, but no incidental catches of SBT are taken by it. At the peak of the fishery, the Western Australian fleet operations were almost continuous with, but generally inshore of, those of South Australia. The demarcation between the fisheries was approximately 125°E. The remaining Western Australian activities are now in the Albany area (Figure 1).
Some occasional SBT-directed trolling activities occurred off the far southern west coast of Western Australia in the late 1970s. There were also reports around the same time that 1–2 year old SBT were taken by trolling for bait by rock lobster fishermen between Shark Bay and the Abrolhos Islands (26°S–28°S; Figure 1). However, the taking of SBT north of 34°S off the west coast has been prohibited since the early 1980s to protect small fish.
2.1.2 South Australian purse-seine/pole-and-line fishery
Experimental pole-and-line fishing during the early 1950s led to steady development of a commercial fishery off the west coast of South Australia (Figure 1) from the mid 1950s, the season extending from mid-December to May, and landings being canned, or exported for canning. Catches averaged 5,000–6,000 mt annually during the later 1970s when experimental purse seining was introduced, at first in competition with the pole-and-line operations. It soon became apparent that catches were enhanced when the vessels worked together, a pole-and-line vessel holding fish at the surface with live bait while a purse seiner set around the fish and pole vessel. This cooperative operation continued until the end of the 1980s, whereupon the involvement of purse-seine vessels diminished in conjunction with the decline in the proportion of the catch destined for canning.
Catches in the South Australian fishery increased to about 14,000 mt in 1982–83 (representing some 1.6 million fish). Subsequently, concern about the extent of reduction in SBT parental biomass prompted the introduction of a quota. Progressive reduction of quotas for the remainder of the 1980s, and diversion of some of the surface activity to longline operations brought the catch to 2,500 mt (some 125,000 fish) in 1990–91. The fleet has declined from a peak of more than 70 vessels to less than 20. The fishery at times took opportunistic catches of albacore and skipjack but there are no other commercial domestic tuna fisheries in the region.
There have been different age groups targeted over the years. Initially (until the late 1960s) the catch consisted predominantly of 3 and 4 year olds, but during the 1970s 2- and 3- year olds dominated. In the 1980s, effort was directed away from very young fish and numbers of 2 year olds in the catch progressively diminished. Fishermen sought to divert product from canning to the Japanese market for fresh or frozen sashimi. This was accompanied by a temporary improvement in representation of 5 to 7 year olds, but by the late 1980s, 3 and 4 year olds were again dominant (Figure 2). Finally, with diversion of surface fishery quota to longlining, those surface operations remaining have avoided 3 year olds and now concentrate on 4 and 5 year olds.
A renewed activity in South Australia in 1990–91, but one unlikely to expand significantly, was the operation of a small commercial troll fishery in the southeast of the state in April-May, air freighting fresh SBT to Japan. Five rock lobster vessels took approximately 10 mt during June and July. The fish were mainly 3–4 year olds.
The most recent developments have been the conversion of some of the surface fleet to longlining, and the establishment of experimental, cage-rearing operations with SBT in South Australia. Longline catches were minor (about 15 mt) in 1991–92, but about 130 mt were held in rearing cages. Fish introduced to cages are captured by surface gear and are in the 3–4 year old age range. It seems probable that expansion of both these alternatives will occur. However, most Australian quota is now committed to Australia-Japan joint-venture longlining operations by Japanese vessels.
Figure 2a. Percentage catch in numbers of 1+, 2+, 3+, 4+ and 5+ to 10+ year old fish in the Western Australia SBT catch, quota years 1959–60 to 1991–92.
Figure 2b. Percentage catch in numbers of 2+, 3+, 4+ and 5+ and 6+ to 10+ year old fish in the South Australia SBT catch, quota years 1963–64 to 1991–92. (Quota year is 1 October to 30 September, with the exception of 1991–92, which extends from 1 October 1991 to 31 October 1992.)
Figure 2c. Percentage catch in numbers of 2+, 3+, 4+, 5+ and 6+ to 10+ year old fish in the New South Wales SBT catch, quota years 1963–64 to 1991–92.
2.1.3 New South Wales purse-seine/pole-and-line fishery
Australian commercial pole-and-line tuna fishing commenced off New South Wales (Figure 1) during the early 1950s, after many years of incidental troll catches of SBT and other pelagics. Production reached approximately 5,000 mt (some 275,000 fish) by the early 1970s with a fleet at times in excess of 100 vessels. The catch was used for canning. Despite introduction of collaborative purse-seine/pole-and-line operations during the late 1970s, and the much more extensive coverage of the fishing grounds by fish-spotting aircraft during that period, the New South Wales surface fishery catch of SBT declined, failing altogether in 1985 and for the remainder of the 1980s. Southern bluefin tuna 2 to 7 years old had been common in the catch from year to year. The dominant age group in number until the late 1970s was that of fish approaching 3 years of age, after which time the representation of younger fish declined (Figure 2). By the 1980s they were absent from the New South Wales catch, and it was only in 1991 that scattered, small, surface schools of SBT were again reported off New South Wales. A small bycatch of SBT was also taken by fishers trolling for albacore, yellowfin (T. albacares) and skipjack.
Poling and purse seining for skipjack have expanded during the late 1980s but to date no incidental SBT catch has been reported. The skipjack season tends to occur later (December to May/June) than the ‘traditional’ SBT season off New South Wales (September to January).
2.1.4 New South Wales longline fishery
A small vessel (10–25 m), domestic longline fishery with yellowfin and bigeye tuna as the target species developed off the central and south coast of New South Wales in the mid 1980s with the successful establishment of air-freight outlets to the Japanese fresh sashimi market. Incidental catches of albacore and SBT were also taken, the latter between March and September in the same area that the surface fishery operated. Up to 175 vessels are licensed in the fishery but only 20 or so vessels reported landing SBT in 1991–92. Whereas albacore are unsuitable for export as sashimi and their market value is low, some of the SBT taken have commanded very high prices (to ¥ 10,000 per kg). The size of the SBT varied from around 15 kg processed weight to over 120 kg (4–15 years old). The quantities currently involved have been small (perhaps about 60 mt in 1991–92) but their value suggests that increases may occur, especially if longline catch rates of SBT continue to increase. It is possible that interaction may develop among longliners, trollers and pole-and-line vessels if surface aggregations of SBT re-appear in quantity off southern New South Wales.
2.1.5 Tasmanian troll and longline fisheries
During the late 1980s, between March and August, small (7–15 m) vessels from Eaglehawk Neck and Hobart on the Tasmanian east coast (Figure 1) trolled a few miles offshore for SBT. The catch, which was air-freighted fresh-chilled to Japan, was about 50 mt in 1991–92 from the fleet of about 20 troll vessels (one longlining also). Most of the fish were 15–25 kg (4 and 5-year olds) but some older and younger fish were also taken. The level of activity is likely to increase, with further diversification to longlining.
2.1.6 Japanese-style longlining in the Australian fishing zone
The waters of what, after 1979, became the 200-nautical-mile Australian Fishing Zone (AFZ; Figure 1) have been fished since the 1950s by the Japanese fleet of large (30–60 m) distant-water longliners. Those vessels operating south of 30°S seasonally targeted SBT, with incidental catches of albacore, broadbill swordfish (Xiphias gladius), bigeye tuna, and sharks. In more northern regions of the AFZ, SBT were incidental to catches of yellowfin, bigeye, marlins (Makaira spp.), albacore, and broadbill.
The size of fish taken by Japanese longliners in the AFZ has varied seasonally and by area. Younger SBT (from 3 years old) were taken from the region of the Great Australian Bight (Figure 1). Off New South Wales, SBT from 4 years to 15–20 years old were taken. Fish of the same general range of ages have been taken recently off eastern Tasmania. Off south western Tasmania, the younger ages have been much less strongly represented, with most of the catch consisting of adult SBT (8 years and older).
When the AFZ was established, Japanese longliners were given access under a licensing arrangement developed bilaterally between Australia and Japan. In the mid-1980s, two Australian-owned, ex-Japanese longliners operated. Since 1990, some of the ‘bilateral’ longliners have participated in an Australia/Japan joint-venture arrangement. There were 42 joint-venture licenses issued in 1991–92, and an allocation of 2,069 mt of Australian quota. From 1990 to early 1992, there were three Australian-chartered, Japanese-style longliners. Each of these groups of longliners was subject to separate licensing conditions and permissible fishing areas.
Access to SBT in the AFZ by ‘bilateral’ longliners has been reduced virtually to the waters surrounding Tasmania, where there is a May to August season off the eastern and southern coasts, and a November to January season off the south west. For the 1991–92 season, a limit of 400 mt (debited against the Japanese global quota) applied, and only 12 ‘bilateral’ vessels operated there. Off the eastern Australian mainland, ‘bilateral’ vessel numbers were limited to 50 in 1991–92 for a maximum of 3,150 days fishing. The western region of the AFZ has a limit of 40 ‘bilateral’ vessels but no limit on total fishing days. These eastern and western activities target other species, and recently the annual SBT catches there have been less than 50 mt and 10 mt respectively.
The Japanese ‘bilateral’ and Australia/Japan joint-venture longline activities off eastern Tasmania are immediately adjacent to, and concurrent with, the Eaglehawk Neck to Hobart domestic troll/longline fishery. Off southwest Tasmania, there is no domestic SBT fishing activity adjacent to the November-to-January bilateral and joint-venture longlining activity.
A major, Japanese longline fishery for SBT occurred annually between April and August off southern New South Wales but it was phased out by access restriction after 1982. It was centred just seaward of the same area, and during the same months as the New South Wales domestic longline vessels. In 1990, 15 Australia-Japan joint-venture vessels and three Australian charter vessels fished the wider New South Wales grounds again, in both cases using Australian quota. Joint-venture vessels were excluded in 1991 and subsequently, but the charter vessels continued fishing there until early 1992, when their operations ceased altogether.
For the 1991–92 season, some of the joint-venture vessels had access to waters of the Great Australian Bight off southern Australia. This area had been closed to Japanese longliners since the mid 1980s, and prior to that (from 1971) had been subject to a voluntary October-to-March closure established by the Japanese fleet to reduce catch of 3- and 4-year-old SBT. The region is immediately adjacent to the South Australian surface-fishery area, which operates during the same months, and size composition of the longline catch there is similar to that in the surface fishery. The experimental longlining mentioned above conducted by modified, Australian, surface-fishery vessels has also commenced in the area, as the Australian fleet seeks to divert activities away from the surface fishery and towards bigeye tuna and larger SBT.
2.2 Japan
Japan is involved in the SBT fishery by way of a distant-water longline fishery which developed in the 1940s to satisfy a demand for tuna exports to canning markets. The fishery moved into the Southern Hemisphere during the 1950s, with SBT activities commencing in the region of the spawning grounds (the Indian Ocean south of Java and off north western Australia) taking post-spawning adult SBT (8–20 year olds). Catch peaked at 78,000 mt (representing some 1,225,000 fish) in 1961, when approximately 150 vessels operated. The catch, destined for canning, was generally held in refrigerated brine. However, SBT was also used in Japan for ‘kirimi’ (fish filleted, sliced and cooked, usually in oil), and this led to expanded use of freezer storage.
At the end of the 1960s activity moved south of the spawning grounds (west of North West Cape; 22°S) and finally spread broadly in the region of the West Wind Drift of the Southern Ocean (35°S–45°S; Figures 3 and 4), extending from the western South Atlantic, eastward to the South Pacific adjacent to the New Zealand east coast (Shingu, 1978). The final product of the catch changed to sashimi because the development of very low temperature freezer storage (<-50°C) enabled vessels to land high-quality SBT even after lengthy cruises.
Figure 3. Fishing grounds of Japanese longliners in the mid-1960s, as shown by average year's hooking rate for each 1 degree square, after operations had spread south from the northeastern Indian Ocean. Coastal distribution of Australia from Robins (1963) and that of New Zealand from McKenzie (1962). Subsequent operations spread more broadly between 40°S and 50°S. (Source: Shingu, 1970.)
Figure 4. Distribution of southern bluefin tuna catch in numbers by Japanese longline tuna fishery, 1970. (Source: Fisheries Agency of Japan, 1972.)
The southern operations extended the range of ages of fish caught to approximately 4 years and older in general. More specifically, younger-aged fish (i.e. including sub-adults) were taken north of 35°S. The main areas were south and east of Australia, off north-eastern New Zealand and off South Africa. Older (i.e. generally adult) fish were more prevalent south of 35°S. The main areas were off southern New Zealand, off Tasmania, off south-western Australia, east of South Africa, and on and south of the spawning grounds.
During the 1970s, SBT catch was in the order of 25,000 mt to 40,000 mt (some 450,000 – 800,000 fish). The fleet increased to a maximum of 250 vessels in 1980, after which economic rationalization of operations, and more recently the advent of quotas and operational restraints, brought about a reduction to around 200 active vessels annually. By the end of the 1980s catch had declined to under 10,000 mt (175,000 fish), and areas of operation had contracted substantially (Nishida and Ishizuka, 1992).
Some components of the fleet moved seasonally to bigeye grounds in the Indian and Atlantic Oceans. Others had moved to yellowfin and marlin grounds in the Tasman and Coral Seas, but this was curtailed by changed 200-mile-zone access conditions in the region. Nevertheless, the capacity to divert seasonal operations to other species, and the increasing price for high quality SBT sashimi, enabled continued seasonal operations on SBT despite the very low catch rates associated with the substantially-diminished parental biomass level.
Prior to contraction of the fishing seasons and areas, there was a range of seasonal patterns of Japanese longline operations. The main seasons by area were February to July off New Zealand; May to August off New South Wales; October to January off south-western Tasmania; year round in the Great Australian Bight (until establishment of the voluntary closure between October and March); October to November and then January to March off Albany, Western Australia; August to December in the south-eastern Indian Ocean; and March to October off South Africa. The SBT fleet consisted of several groups of vessels with different fishing campaigns. One group fished progressively from the southern Atlantic in April across to Tasmania until mid-January. Another fished the grounds off Tasmania, New Zealand and the south-eastern Indian Ocean. There was also a group fishing off New Zealand, New South Wales and in the Coral Sea.
The main SBT activities were undertaken during the second and third quarters of the year, with diversion to other species like bigeye tuna more common during the first and fourth quarters when SBT meat condition was poorer.
Currently, the main fishing areas are the AFZ waters adjacent to eastern, and to a lesser extent, south-western Tasmania, the Southern Ocean adjacent to south-western Australia, the Southern Ocean to the south-west and south-east of South Africa, and waters adjacent to south-eastern and southern New Zealand (Nishida and Ishizuka, 1992). No Japanese longliners target SBT on the spawning grounds or the region immediately to its south, but incidental catches are taken during bigeye- and yellowfin/striped marlin-directed operations. Size composition varies among the main fishing areas (Figure 5). The 1991–92 fishing seasons were March to August off New Zealand, May to September off Tasmania, April to July off South Africa, and August to October off southwestern Australia and the southern Indian Ocean. As part of a cooperative, SBT size-composition monitoring programme conducted by Australia, Japan, and New Zealand a small number (17 in 1991–92) of special-quota vessels continued operations after the main seasons were closed.
During the 1970s and 1980s the establishment of 200-mile economic zones proliferated, with the result that access to previously-important fishing areas was increasingly restricted. Consequently, Japan sought other countries in order to establish joint-venture longline arrangements. However, as regards SBT activities, only Australia and New Zealand were involved in these ventures.
2.3 New Zealand
2.3.1 South Island handline/troll fishery
The observation that large (15–20+ year old) adult SBT were attracted to offal from factory trawlers off the west coast of the South Island led to development in 1980 of a handline/troll fishery between 41°S and 43°S (Figure 6), supplying SBT to the Japanese sashimi market. Catch increased to 305 mt in 1982 then declined steadily, reflecting the decline in SBT parental biomass. Approximately 25–30 vessels are engaged in the fishery, with a season which has contracted to July to August (Murray and Burgess, 1992).
2.3.2 South Island longline fishery
Declining catches in the handline/troll fishery led some fishermen to diversify into small vessel (15–30+ m) longlining in 1988. Now about six to eight multi-purpose vessels (one a 50 m former Japanese longliner) operate, some with other species as target, and extending in range and in season beyond that of the handline/troll fleet (Murray and Burgess, 1992). Their catch in 1990 was 286 mt, and size composition was similar to that of the catch from licensed Japanese longliners and joint-venture charter longline vessels in the New Zealand Exclusive Economic Zone (NZEEZ) (Figure 6).
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Figure 5. Preliminary 1991 percent-frequency distribution of catch-at-age in Japanese southern bluefin tuna longline statistical areas (Area 4: New South Wales; Area 5: northern New Zealand; Area 6: southern New Zealand; Area 7: southern Australia; Area 8: southeastern Indian Ocean; Area 9: south of Africa). Age given in years. (Source: Nishida and Ishizuka, 1992.)
Figure 6. Locations of catch of southern bluefin tuna by New Zealand domestic (triangles) and foreign (crosses) vessels. Positions represent locations of daily position reports by domestic vessels and start-of-set locations for longliners, for the period 1980–88. The general outline of the New Zealand EEZ is shown, as well as the Auckland Fisheries Management Area (shaded). (Source: Fisheries Research Division, Ministry of Fisheries and Agriculture, New Zealand.)
2.3.3 Japanese-style longlining in the New Zealand exclusive economic zone
The waters of what became the NZEEZ in 1978 have been fished since 1956 by the Japanese distant-water longline fleet and, perhaps since the late 1950s and mid 1960s, by longliners from Korea and Taiwan, until the establishment of the NZEEZ. Currently Japanese (and until 1989 Korean) longliners have been licensed to operate in the zone (Murray and Burgess, 1992). Two fishery components are involved. The ‘southern’, which operates between February and August, involves Japanese longliners which target SBT and to a much lesser extent bigeye and swordfish. It is located east and west of the South Island (February to June) and east of the North Island (May to August) (Figure 6). SBT catches are incidental in the other (northern) component, which is located north of the North Island between June and August, and which previously targeted albacore (Korean vessels) but which now target only bigeye and swordfish (Japanese vessels). It has been restricted in season since 1987 by an October-to-May closure in the Auckland Fisheries Management Area (Figure 6) this enclosure is designed to reduce competition with a domestic game fishery for striped marlin. All Japanese-style longlining is excluded from the 12-mile territorial sea at all times.
Over 7,000 mt of SBT were taken annually in the NZEEZ by Japanese longliners when the NZEEZ was first established, but now the catch is less than 1,000 mt, the fleet having decreased from around 90 vessels to less than 40, only 25–35 of which target SBT. The size composition of the catch (Figure 7) shows progressive absence of younger individuals during the 1980s but an increase in 1990 and 1991, in conjunction with an increase in activities west of the South Island and east of the North Island. The SBT catch reported from northern waters by Korean and Japanese longliners targeting other species, is less than five mt; no details of size composition, or indication of the completeness of these bycatch reports are available.
Since 1989, four to five New Zealand/Japan joint-venture charter vessels have operated in the NZEEZ. The four which operated in 1991 fished alongside the small, domestic longline vessels for part of their season, and among the Japanese licensed longliners for the remainder. Their catch in 1990 was 233 mt, and the size composition of the catches from the domestic fleet was virtually identical to that from the Japanese licensed longliners (Murray and Burgess, 1992).
Historic SBT catch rates in the ‘northern’ fishery area were high (Figure 8), peaking from September to November (Shingu, 1970). Part of this season is now curtailed by the October-to-May closure, but if the availability of smaller (< 40 kg) SBT increases in the NZEEZ, then an increased by-catch of smaller SBT from the region might be anticipated.
2.3.4 Albacore surface fishery
A troll fishery for albacore has operated off the west coast of the South Island from January to March since the 1960s, but has no by-catch of SBT. During the mid to late 1980s a major drift gillnet fishery developed in the Tasman Sea between the AFZ and NZEEZ, and also in the region of the Sub-Tropical Convergence Zone in the western South Pacific. Reports from monitored transhipments and observers indicate that, despite substantial incidental catches of a range of pelagic species, the catch of SBT was extremely low and the fish were large. This is consistent with the reduced abundance of surface aggregations of young SBT off New South Wales and their poor representation in NZEEZ longline catches at that time. If the abundance of young SBT in the Tasman region increases, there may be potential for an increased by-catch of SBT from the troll fishery. There would also have been potential for increased drift gillnet by-catch, but since 1 July 1991 the South Pacific has been subject to a closure for drift gillnetting in accordance with UN Resolution 44/225.
Figure 7. Weight distribution (5 kg size classes) of southern bluefin tuna caught by foreign licensed longline vessels in the New Zealand EEZ, 1980–91. (Source: Murray and Burgess, 1992.)
Figure 8. September to November changes in extent of longline fishing grounds and in average hooking rate for 1965–67. (Source: Shingu, 1970.)
2.4 Indonesia
Indonesia lies immediately north of the SBT spawning grounds. The spawning season extends from September to March with a peak in January and February. Japanese distant-water longline vessels commenced operations on SBT there, but the poorer meat quality of post-spawning fish prompted dispersal of Japanese SBT target activities further south. While adult SBT can be anticipated seasonally on the spawning grounds, it is a region where the other pelagics targeted by longlines are also prevalent. Longlining, and hence the catching of SBT, continues there, with vessels from Japan, Taiwan, Indonesia and Korea involved. The Japanese vessels target bigeye tuna, and this and yellowfin are the main targets of the Taiwanese and Korean vessels (Institute of Oceanography, National Taiwan University, 1991; Park, et al., 1991). Indonesia has been promoting the development of fresh tuna exports to Japan (Sodikin and Siregar, 1989). The price for fresh SBT makes it a target species for Indonesian longliners.
Indonesian domestic longlining commenced in 1972 in the Banda Sea (Figure 9). It has developed rapidly since 1985 with the strong demand for fresh tuna especially in Japan. The domestic fleet increased from 18 in 1979 to 151 in 1990, but there were also 341 foreign longliners operating in Indonesian waters by 1989 (Naamin and Gafa, 1991). The longlining activities mainly catching SBT are those on the Indian Ocean side of the archipelago.
Figure 9. Yearly fishing grounds of southern bluefin tuna in southern Java and Nusatenggara waters, 1978–88. (Source: Bahar and Naamin, 1989.)
The main SBT fishing ground for Indonesian vessels is located between 103°E and 128°E, and 7°S and 17°S (Figure 9), with activities moving closer to the 12-mile territorial waters in August-October. Catches averaged four mt annually between 1978 and 1988, with fish ranging in size from 61–164 kg (Bahar and Naamin, 1989).
Indonesian domestic vessels undertake trips of short duration (up to 14 days) and air freight their catch fresh to Japan. The domestic catch from the Indian Ocean region is augmented by the catches of Indonesia/Taiwan joint-venture longliners. These range from smaller longliners returning fresh fish after trips of short duration, to freezer vessels carrying out broader-ranging operations in the Indian Ocean. The extent of the SBT catch of these vessels, which may have a range of target species, is not known. It is a valuable component and may have been in the order of 100 mt in 1990 (Naamin, pers. commun.).
Japanese imports of fresh and frozen bluefin from Indonesia amounted to 150 mt and 15 mt (whole weight) respectively in 1991 (Japan Tariff Association, various). There is no indication of the proportion of northern and southern bluefin on these imports but it can be assumed reasonably that the imports from Indonesia are all SBT. Half of the Indonesian SBT catch destined for export fresh to Japan is classified as unsuitable and consumed locally (Davis, 1992). On this basis, the additional 75 mt would suggest a total Indonesian domestic and joint venture SBT catch of the order of 240 mt for 1991.
Waters within the Indonesian Archipelago support a component of the southwest Pacific tuna fishery. Yellowfin and skipjack tuna are the main target species. No SBT by-catch is reported. The waters are further north and more tropical than those where SBT are distributed.
2.5 Taiwan
Taiwanese involvement in the SBT fishery has probably occurred predominantly through distant-water longline operations in the South Atlantic and Indian Oceans, and to a lesser extent through bycatch in drift gillnet operations. This latter catch will have ceased if the United Nations resolution requiring global cessation of driftnetting by the end of 1992 has been effective.
Longliners from Taiwan commenced operations in the Indian Ocean in 1963, at first with albacore as the target species, then also yellowfin and bigeye (Hsu and Liu, 1990). In the mid-to late-1980s, ‘regular’ longline operations for albacore were concentrated between 10°S and 40°S latitudes. Deep longlining for bigeye was located mainly between 20°N and 15°S, but increasing activity occurred from 1986 to 1988 between 25°S and 40°S, especially in the south western Indian Ocean (Figure 10). In 1988 monthly mean weights of bluefin (assumed to be SBT) in Indian Ocean longline catches ranged between 31.58 kg (July) and 68.77 kg (September). A fleet of 187 vessels operated.
There were also drift gillnet vessels operating in the northern and southern Indian Ocean from 1983, targeting albacore tuna (Figure 11). Vessel numbers reached 150 by 1987–88. Hsu and Liu (op.cit.) reported the average weight of albacore taken by drift gillnet as nine kg, and of bigeye as 26 kg, but no details were given for SBT.
Japanese longliners achieved good SBT catch rates between 30°S and 40°S when their SBT operations spread to the southern Indian Ocean (Figure 3). The catches probably consisted of a larger proportion of young SBT in these latitudes than between 40°S and 45°S where operations are now concentrated. Broad availability of younger SBT in the southern Indian Ocean during the late 1970s and early 1980s was diminished because of the build-up in Australian catch of juveniles. The subsequent major reductions in Australian juvenile catch might be expected to have resulted in substantial escapement of younger fish to the area, given earlier examples of rapid westward movement of some of the SBT tagged on the Australian fishing grounds. Representation of small SBT increased in Japanese catches off south-west Australia and South Africa at the end of the 1980s. If this results from the broader distribution of young fish between 30°S and 45°S westwards in the southern Indian Ocean, then increased Taiwanese SBT catches might be expected.
Figure 10. Distribution of annual Taiwanese “deep” longlining effort in the Indian Ocean, 1986–88.
(Source: Hsu and Liu, 1990.)
Catch statistics published by the Indo-Pacific Tuna Programme indicate that the total annual catches of SBT in the Indian Ocean ranged between 4 mt and 266 mt from 1970 to 1990 for vessels from Taiwan (Indo-Pacific Tuna Management and Development Programme, 1992). This seems inconsistent with Taiwan Statistical Yearbook figures for ‘bluefin’ (the statistics do not discriminate between northern and southern bluefin) which, if landing ports and ocean areas are considered, would suggest annual catches of SBT considerably in excess of 500 mt for the late 1980s (Taiwan Fisheries Bureau, various). Japanese imports of fresh and frozen bluefin from Taiwan amounted to 232 mt and 1,157 mt respectively in 1991 (Japan Tariff Association, various; processed weights). There is no indication of the breakdown between northern and southern bluefin but fresh imports from Taiwan entering Japan from April to July are presumably northern bluefin, whereas frozen bluefin arriving year-round would be from the distant-water longline fleet. The most evident feature of the pattern of bluefin imports by Japan is the major increase from Taiwan after 1988. An examination of price for frozen SBT from Taiwan shows a similar large increase at that time. This change coincides with the imposition of quotas on the Japanese SBT fishery. The first quota involving a reduction of Japanese catch was agreed in late 1988 to come into effect in 1989. The increased Taiwanese imports, at sashimi prices, commenced in that latter year. There are anecdotal reports of Taiwanese vessels moving onto traditional Japanese SBT fishing grounds after closed seasons forced Japanese-flag vessels to move. This is consistent with the sudden increase in supplies of sashimi-grade bluefin from Taiwan to Japan, most of which might reasonably be assumed to be SBT.
Figure 11. Accumulated number of months of Taiwanese large-scale pelagic drift gillnet effort in 50 squares in the Indian Ocean, 1987–88. (Source: Hsu and Liu, 1990.)
Actual SBT catch by Taiwan is difficult to determine because it appears that some Taiwanese bluefin catches by-pass the statistical collection. For example, the 1980 Taiwanese production statistics report a global bluefin catch of 179 mt, whereas correspondence in 1983 from the South African Sea Fisheries Research Institute to the Australian Trade Commissioner in South Africa advised that in 1980, 14,800 mt of tuna were transhipped in South Africa by vessels from Taiwan with SBT representing 7% of 11,982 mt of that tuna (i.e. 1,001 mt). The correspondence advised that the bulk of the catch transhipped would have been made in the mid-Atlantic and even off the coast of Brazil, and that “the SBT were caught by boats fishing more to the south than most of the fleet”. Again, the 1991 Taiwanese production statistics report a total bluefin catch of 960 mt (Weng, pers. commun.), whereas 1991 bluefin imports to Japan from Taiwan and Singapore (the latter presumably also originating from Taiwanese vessels) were 1,389 mt and 67 mt processed weight respectively. As these would not include the Indian Ocean drift gillnet bluefin catch (which would not be suitable for export to Japan as sashimi) the overall 1991 bluefin production would have exceeded 1,456 mt.
2.6 Korea
The Korean distant-water longline fleet has taken SBT as an incidental component of catches. Published statistics for the Indian Ocean report that Korean SBT catches ranged between 7 mt and 500 mt per year from 1971 to 1978, and then ceased (Indo-Pacific Tuna Management and Development Programme, 1992). As, progressively, Korean longliners have concentrated activities in tropical areas for bigeye tuna during the 1980s, only small incidental catches of SBT would be expected in recent years.
The virtual absence of incidental Indian Ocean SBT catches after 1978 seems inconsistent with the species composition which might be anticipated in some of the areas and at some of the times where longline operations are reported in published global five degree-square Korean longline statistics. As an example, operations off southwestern and northwestern Australia in 1983 and 1984 (Figure 12) occurred in areas where SBT have been well represented in historic Japanese longline catches (Figure 3 and 4) but the 5 degree-square statistics do not include reports of any SBT (National Fisheries Research and Development Agency, 1988). Distribution of more recent (1988 and 1989) Korean longline activities in the Indian Ocean (Park et al., 1991) include areas where Indonesian vessels using deep longline gear target SBT (Figure 9).
Japanese imports include bluefin from Korea (Japan Tariff Association, various; processed weights). The main imports are fresh bluefin which, taken between May and November like the Taiwanese fresh bluefin exports to Japan, can be assumed to be northern bluefin tuna from adjacent fishing grounds. Japanese frozen bluefin imports from Korea are less certain as to species. They amount to significantly less than those from Taiwan and show no recent increases. This is consistent with the recent concentration of Korean longlining operations in tropical areas. However, there are still operations in temperate areas of the North Pacific, so the frozen bluefin imports to Japan, given their high price, probably represent northern bluefin from those activities.
2.7 South Africa
South African catches of SBT were uncommon until the 1950s (de Jager et al., 1963), when handlining, and then in the early 1960s experimental Japanese-style longlining, by research vessels indicated promising catches of SBT, albacore, yellowfin, and bigeye tunas off the west coast. Southern bluefin tuna was described incorrectly as Thunnus thynnus orientalis, which does not occur in the South Atlantic or southwestern Indian Oceans. Commercial longlining developed rapidly within 240 km of the coast in the area between 32°S and 35°30'S (Negpen, 1970), but then rapidly declined after 1963 because returns were uneconomic. This was partly because catch rates had declined. In the interim, the SBT catch, taken predominantly during the southern winter, reached around 400 mt in 1963, with fish ranging in size from 90–170 cm. Japanese longliners fished on the same grounds (and over a wider area) during the same period.
Recent catches of SBT by domestic South African fisheries appear to be insignificant (Molteno, 1986; Vere Shannon et al., 1989). Correspondence in 1982 to CSIRO from the South African Department of Agriculture and Fisheries indicated that about 20 mt of SBT had been taken by pole-and-line in the vicinity of the Vema and Tripp seamounts (30°S, 8°E and 29°S, 14°E respectively). Molteno reports: “The southern bluefin tuna is caught in the southern Atlantic entirely by longline and surface schools have not been observed in recent years”. Vere Shannon et al. (1989) indicate “Southern bluefin tuna (nowadays 25 kg commercially but up to 80 kg in the early 1960s) are more common off southern Africa than northern bluefin and were extremely abundant off the Cape of Good Hope during the early 1960s, mainly during the winter but also in early spring.” A South African catch of one mt of ‘bluefin’ in 1989 (in a total South African tuna catch of 2,600 mt) and zero bluefin catches in 1988 and 1987 are reported in South African statistics (Anon., 1990)
Figure 12. Distribution of Korean longline effort in the Indian and western Pacific Oceans in 1983 and 1984 as reflected by catches of all species. (Source. National Fisheries Research and Development Agency, 1988.)
There are indications of previous high SBT catch rates by the Japanese longline fishery from areas now encompassed by the South African 200-mile fishing zone, especially closely adjacent to south western South Africa (Figure 3). The size composition reported included fish from 90 cm to 150 cm (Shingu 1970), with a large proportion from 90–120 cm (3–7 year olds). If abundance of younger age classes of SBT increases in regions away from southern Australia subsequent to the reduction in surface fishing activities there, it is possible that incidental catches of SBT in regions like southwestern South Africa might increase. However, Japanese longlining activity tends to be concentrated in more southern areas and beyond the South African 200-mile fishing zone.
Although no domestic catch of SBT is now reported, South Africa, like Singapore, acts as a trans-shipment or unloading base for Taiwanese longliners. Japanese import statistics from South Africa for 1989 indicate a substantial quantity (99 mt whole weight) of bluefin, presumably all of which was SBT. However, this was an isolated instance, and SBT imports are rare in most years.
2.8 South America
Japanese longline vessels fishing towards the eastern edge of the South American continent have taken SBT (Figure 4), and it is probable that the species can occur within the 200-mile fishing zone of Argentina. In the southeastern Pacific off Chile, a ‘Japan Marine Resources Research Center’ experimental longline cruise around the beginning of 1980s took a by-catch of a single SBT. While the species may be distributed within the 200-mile zones of these two countries, there are no reports indicating that catches of any significance occur.
3. RECREATIONAL FISHERIES
Recreational fishing for SBT predominantly focuses on juveniles which are easily accessible on, or closely adjacent to, the Continental Shelf. Most activity occurs around southern Australia, but reports have also indicated that recreational fishing has taken place in South Africa at times. A small New Zealand recreational fishery off the southwest coast of the South Island has not reported SBT catch for many years.
3.1 Australia
Recreational angling for ‘oceanic’ fish like SBT was not common until the increased availability of inexpensive, ocean-going trailer boats. Originally the sport was the domain of anglers with ocean-going cabin cruisers. Now, there is a large fleet along the eastern and south-eastern Australian seaboard, and a lesser fleet off South Australia and Western Australia.
3.1.1 New South Wales
From as early as 1936 (Roughley, 1951) the southern coast of New South Wales has been an important recreational fishing area for SBT. Troll fishing along the Continental Shelf routinely provided catches of 7–15 kg SBT from July/August to January, in the same general area as commercial operations but inshore of them. Catch is likely to have been in the order of 50–100 mt in the 1970s, but gamefishing clubs report a virtual cessation of catches after 1980. The absence persisted until July 1991, when small, scattered catches were taken again by recreational anglers in some of the traditional areas. Recreational anglers belonging to fishing clubs have been concerned about the state of SBT stocks to the extent that the species no longer scores competition points on landing. Instead, club anglers are encouraged to tag and release the species as part of the New South Wales recreational, gamefish-tagging programme. The greater proportion of recreational anglers do not belong to clubs, but their operations are subject to legislation (not specifically directed at SBT) which imposes a daily bag limit of 2 fish per angler. Trailer vessels have been increasing in popularity along the southeastern seaboard of Australia, and the number capable of operating in the SBT area in quiet weather is probably in the order of 1,000 now. There is thus a potential for high recreational fishing effort if SBT concentration builds up off New South Wales.
3.1.2 Western Australia
The main centre for recreational tuna fishing is the area adjacent to Busselton, south of Perth. Smaller-scale activities operate off the western south coast (from Albany) and in the Perth region. Up to 100 small vessels might participate seasonally (summer-holiday months), especially on weekends, with four SBT, 1–2 years old, representing a reasonable catch. On this basis, the annual recreational catch is estimated to be less than 50 mt for the State.
3.1.3 South Australia
The main centre of recreational tuna fishing in South Australia is near Port Lincoln where commercial pole-and-line fishing commenced. However, the number of vessels is small because the waters are exposed, and weather conditions restrict access to the generally small vessels involved. Recreational tuna fishing activities were also carried out on a small scale near Cape Jervis, south of Adelaide, up to the early 1980s, but progressive contraction of fish aggregations westwards led to their cessation. A similar decrease in availability occurred in the southeast of the state. In that area, the number of vessels was again small, except each Easter when a fishing tournament for SBT took place, involving around 20 or 30 trailer vessels.
In some years during the late 1970s and early 1980s, the commercial purse-seine and pole-and-line fisheries extended to this southeast region of South Australia later in the season. However, these commercial operations also contracted westwards during the late 1980s. Following the introduction of restrictive quotas in the Australian surface fishery, the westwards contraction was reversed to the extent that, in 1990 and 1991 (but not in 1992), recreational fishing reports suggested a reappearance of fish in the southeast of the state.
The annual recreational catch for the State is unlikely to have exceeded 20 mt annually, and the fish have usually been 5–20 kg (2–4 year olds).
3.1.4 Tasmania
The SBT has been the target of seasonal (January to August) recreational tuna fishing activities, mainly adjacent to Eaglehawk Neck in eastern Tasmania. One trophy for the heaviest tuna caught each year has been presented since 1958. A gamefishing charter-boat operator at Eaglehawk Neck has maintained records of his daily SBT catches since 1965. Concurrent with the rapid increase in catches of 2–3 year old SBT by the Australian commercial surface fishery at the end of the 1970s, and the collapse of the New South Wales commercial fishery, his daily catch rate (3.5–14.5 fish per day) declined until 1984 when no SBT were caught. Subsequently, when quotas reduced the commercial catches, his daily catch rates increased, but remain lower (0.5–4.8 fish per day) than the average catch rate prior to the decline. The number of vessels probably does not exceed 50, with an annual catch probably less than 25 mt.
3.2 South Africa
Smith and Heemstra (1986) comment that in South African waters SBT is “known only from long-line catches off the Cape region during winter”, whereas for northern bluefin tuna (Thunnus thynnus) “schools congregate during summer in the Agulhas Bank area and frequently enter False Bay”. Negpen (1970) makes reference to “big Atlantic bluefin tuna Thunnus thynnus thynnus caught in False Bay by sport fishermen during the summer months”. However, Molteno (1986) reports “In the late 1950s bluefin tuna schools entered False Bay and anglers using spinners caught a number of these fish by casting off the rocks at Cape Point. Most of these tuna were young southern bluefin.” Anglers may have problems discriminating between the two bluefins, but it would seem likely that winter catches would involve SBT. In a personal communication, Malcolm Bertani of the Bureau of Resource Sciences reports that as a recreational angler he trolled for and caught SBT in winter within sight of land from Cape Town during the 1960s. However, their abundance declined to the extent that by the end of the 1970s they were no longer taken there.
If ‘young’ southern bluefin are involved in recreational catches off South Africa, their availability during the 1980s would likely have been poor if recruitment to the area was subject to the same influences that led to the experiences off south-eastern Australia. If the reappearance in recreational troll catches off Australia is indicative of broader escapement of juveniles, then South African recreational catches might also be anticipated to increase.
3.3 New Zealand
Recreational fisheries for striped marlin and yellowfin tuna operate in northern New Zealand waters in summer months. These fisheries catch other tunas (e.g., albacore, skipjack, and bigeye) but do not catch SBT. A small, recreational fishery for SBT operated off the south west coast of the South Island in the early 1980s but caught few fish. No recreational catches have been reported in that area for many years (Murray, pers. commun.).
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