Capture-based tuna aquaculture

Capture-based tuna aquaculture in Japan

Motoo Inoue, a Tokai University Professor financed by the Fisheries Agency of the Japanese Agriculture Ministry, started experimentation on bluefin tuna culture in 1970 (Inque 1973a,b). The aim was to grow out juveniles to commercial size and, in the future, to actually breed the bluefin tuna. The ethology and physiology of the species created several problems in adapting the species to captivity, resulting in low survival rates due to the stress during capture.

The results of three years of experiments were quite poor from a practical point of view (Ueyanagi et al. 1973; Le Gall 1974, 1977; Harada 1979), but the way was opened for the capture-based aquaculture of bluefin tuna. Eight companies and organizations currently farm bluefin tuna in various locations in Japan: 3 in Okinawa, 4 in Nagasaki, 2 in Wakayama, 6 in Amami and 3 in Ehime and Kochi (Ikeda 2003).
In contrast with tuna culture methods elsewhere, juveniles of 150-500 g body weight are caught off the coastal areas of Japan and are reared for 3 to 4 years in net cages until their body weight increases to between 30 and 70 kg, when they are harvested.

The trend in Japanese bluefin tuna capture-based aquaculture production from 1998 to 2001 is shown in Figure 90.

Figure 90. Production of capture-based tuna aquaculture in Japan (Ikeda 2003)
The most severe problem for Japanese bluefin tuna capture-based aquaculture is supplying fingerlings to culture farms. Even after capture, the newly-caught young fish react strongly to the stress of their capture and confinement. Their skin is also delicate, and it is damaged easily by mishandling. As a result, mortality rates are high at first. Fish which survive and acclimatise to farm conditions remain susceptible to mortality from sudden changes of climatic conditions, e.g. a fall in water salinity due to typhoon and monsoon rains, or a drop in the oxygen level (Nash 1995).
It is also necessary to improve the rearing techniques used during growing out. The loss of juvenile and young adult bluefin tuna is often caused by collisions with the walls of tanks or nets, which fatally damage the bones of the vertebral column and the parasphenoid (Miyashita et al. 2000). The high number of deaths caused by bumping into the tank and net-pen walls at dawn can possibly be attributed to visually disoriented fish. One experiment found that there is an incompatibility of the retinal adaptation with the change in the ambient light intensity,

a problem that could cause the visual disorientation of the fish (Masuma et al. 2001). It is therefore possible that these visually disoriented juveniles are not able to control their high power swimming properly (Masuma et al. 2001). As capture-based fingerlings are difficult to obtain and the supply is uneven, the industry must seek to rely on hatchery-produced fingerlings. A new and important goal was finally reached in June 2002 (Box 1).

Box 1. A mark of the future: rearing tuna in a hatchery
JAPAN RESEARCHERS BREED BLUEFIN TUNA FULL CYCLE FOR THE FIRST TIME
For the first time, in June 2002, researchers at the Kinki University in Wakayama Prefecture successfully completed the full life-cycle of bluefin tuna. While Kinki scientists mastered the breeding of bluefin tuna as early as 1979, the fish have not been able to survive past an early age until this year. On June 23, an artificially reared adult bluefin tuna produced eggs for the first time (www.intrafish.com). The fish spawned one million eggs and the achievement may pave the way for full-scale farming of the species in the future.
The Japanese government has promoted a “tuna liberation project” in the past. Since 1993, the Fisheries Agency in Japan has spent ?1.2 billion in establishing the bluefin tuna fish rearing and spawning in a facility - Amami Oshima. After this incredible achievement of completing the full life-cycle of tuna, it will be possible to increase the stock by reintroducing fingerlings in the wild.

 

Capture-based tuna aquaculture in the Mediterranean

In recent years, bluefin tuna culture has spread throughout the Mediterranean. This expansion is directly related to the interest and development of the Japanese market. The culture is specifically aimed at producing tuna that have the optimal fat content demanded by the “sushi” and “sashimi” market, and both fresh and frozen tuna farmed products are exported to Japan. In Japan, one kilogram of bluefin tuna can be sold for as much as US$ 430. About two thirds of the Mediterranean bluefin tuna that are exported to Japan are from capture-based aquaculture.
Tuna farming in the Mediterranean is expanding and the production accounts for more than half of the global total. The first commercial tuna farming operation in the Mediterranean area started in 1979 in Ceuta (Spain). Large, post-spawned lean tuna were captured in traps on their way out of the Mediterranean, put in large pens and fattened. As the fish were obtained from traps, the quantities raised every year were limited to a maximum of 200 tonnes (Miyake et al. 2003). Now, tuna are reared in several locations in the Mediterranean (Figure 91). The main producers are Spain (Murcia region), Malta, and Croatia, which together accounted for more than 11 000 tonnes in 2001. The Murcia region (Spain) alone exported more than 7 000 tonnes to Japan, worth more than € 150 million. The trend in the main Mediterranean tuna capture-based aquaculture producing countries for 2000 and 2001 is shown in Figure 92.
Mediterranean tuna farming is based on catches taken from wild populations (of different sizes), which are moved alive to floating cages in offshore areas. The fish are then kept in large cages for variable periods, ranging from a few months to years, depending on the farming location and fish size. In Malta, fish are put in the cages from May-July and kept there until October-January. The fish ranged from 80 to 250 kg in 2000 and from 50 to 620 kg in 2001. Two farms existed in Malta in 2001, when about 1 200 tonnes was exported. Three more companies were expected to start tuna farming around the Maltese Islands by 2003 and export figures were expected to reach 2 500 tonnes/year (Peric 2003b).

Figure 91. Location of capture-based tuna aquaculture in the Mediterranean
Figure 92. Capture-based aquaculture production of the main Mediterranean producers (2000-2001)

The capture-based aquaculture of tuna in Spain began in 1996 in the Province of Murcia. Tuna farmers are grouped within the Spanish bluefin tuna farmers association (ASETUN). The fish supply comes from purse seiners in the western Mediterranean, particularly around the Balearic Islands. The fish range from small (20-90 kg) to medium size (80-120 kg), and are mostly pre maturity. Up to now, no fish are kept more than 10 months in this location (Miyake et al. 2003). Project proposals for new tuna farms have been submitted to virtually all autonomous government regions along the Spanish Mediterranean coast, from Andalucia to the Balearic Islands, including Catalunya (Tudela 2002b).
During the five years 1997-2001 bluefin tuna farming in Croatia averaged about 2 500 tonnes of harvested fish per year. The industry consists of six commercial companies using nine lease sites (Katavic et al. 2003a). Here, the capture of juveniles occurs at the end of spring to early summer. The individuals captured range from some extremely small fish (less than 10 kg, including undersized or just legal minimum size set by ICCAT at 6.4 kg) to small fish (20-80 kg), These are caught by the Italian and Croatian purse seiners in the Adriatic Sea. The farming period differs widely between farms, but usually lasts 2-6 months, while the smallest specimens are usually kept in cages to grow on for two or three years. Small tunas usually dominate the catch composition in the Adriatic Sea (Katavic, Vicina and Franicevic 2003a).
Experiments were carried out in Italy from 1978 to 1982, when some large bluefin tuna were cultured using a small floating cage in the Scopello trap (Sicily). However, commercial capture based aquaculture of tuna did not start until between 1999 and 2000 in the south-west of Sicily, and in 2001 in the Central Adriatic Sea (Miyake et al. 2003). 100 medium sized tuna were farmed in Sicily in 1999; in 2001, 500 small tunas were farmed in the central Adriatic sea, four miles off Ortona. These two farms were built for experimental use. In 2001, a commercial farm was built near Trapani on the Tyrrhenian coast, and 400 tonnes of medium to large tunas were farmed (Miyake et al. 2003). Tuna farming in Italy is expanding, but it is meeting strong opposition from environmentalists.
In Morocco, experimental culture of bluefin tuna started in the mid 1990s. The Moroccan Kingdom and the Japanese Government undertook a joint venture: a large scale experimental project in the North-East of Morocco, on its Mediterranean Coast. Its main purpose was to develop the technology for artificial breeding. Two groups of bluefin tuna broodstock were kept in floating net cages moored in the open sea. The first group was composed of 75 giant bluefin tuna with a mean body weight of about 250 kg that increased to an average of 400 kg after three years of rearing. The second group was composed of 106 young bluefin tuna, which had an average of 55 kg mean body weight, which attained 350 kg after four years of rearing (Nhhala 2002).
One tuna farm in Turkey is situated off the southern coast and uses a cage 150 m in circumference. With a net depth of 20-25 m, this cage provides a culture volume of about 50 000 m3. At a density of roughly 2-3 kg/m3, up to 130 tonnes of fish can be stocked in each cage (Agius 2002).
The rapidly growing practice of bluefin capture-based aquaculture in the Mediterranean has created a series of difficulties for the estimation and reporting of related fishery statistics. At present, fishery statistics are based on catches, while production from capture-based aquaculture is prepared from export data. The primary reason is the lack of accurate estimates for the total weight and size composition of the catch. The problem is due to the transfer of live fish caught from the wild, and the solutions proposed so far (e.g. the use of underwater cameras to count the transferred fish) are not very precise. Therefore, the average weight of the bluefin tunas caught is only a rough estimate, made in order to calculate the total weight of the fish transferred to the cages. There is also a lack of information on growth and conversion rates in cages. At present, ICCAT estimates for the gain in weight of tunas during the capture-based aquaculture period is an average of 25% of their body weight. This leads to a conversion factor of 0.8; this is applied to farmed products imported by Japan to back-calculate capture weight.

 

Capture-based tuna aquaculture in Mexico and the USA

Tuna farming began in 1996 in Mexico, where it currently produces 3% of global output. The majority of operations are located on the Pacific side of the Baja Peninsula (Sylvia, Belle and Smart 2003). Typical size at capture ranges from 15-45 kg, and weight gains can range from 30-90% of initial weight with the production cycle typically being 3-6 months, as in other parts of the world. Mexican farming operations have grown from less than 50 tonnes/year to 600 tonnes/year during the last five years. The original farms were Mexican owned and operated, but the current production companies are various combinations of Mexican, Australian and Japanese partnerships. Fourteen new tuna lease applications were under review in Mexico in 2002.
In 2002, investigations were in progress for the development of tuna farming off the west coast of the United States - particularly in southern California - and also off the coasts of Hawaii (Sylvia, Belle and Smart 2003).

Capture-based tuna aquaculture in Australia

Australian operations started in 1990 near Port Lincoln (South Australia) and, by 2002, had developed into the largest farmed seafood sector in Australia (Clarke 2002). The development of the southern bluefin tuna capture-based aquaculture industry became possible due to collaboration between the Tuna Boat Owners Association of Australia (TBOAA), the Japanese Overseas Fishery Cooperation Foundation and the South Australian Government.
The trend in Australian capture-based tuna farming production from 1992-2001 is shown in Figure 93. Production figures reflect culture periods spanning two years, and consider harvesting strategies that vary from three to ten months after capture. In 2000/2001, harvest volume peaked at 9 050 tonnes (Clarke 2002), representing almost 40% of the global capture-based aquaculture production of tuna at that time (Figure 88). By 2002, the industry consisted of about 16 commercial companies. Southern bluefin tuna weigh 15-25 kg at capture, and are harvested progressively from the cages after 3-10 months. The average weight increases by 10-20 kg over the culture period (Clarke 2002).

Figure 93. Australian production of southern bluefin tuna (Thunnus maccoyii) through capture based aquaculture [Note: production data span the period between October and September the following year]

 

 

Capture-based tuna aquaculture in Canada

In 1975, American enterprises and Japanese specialists started capturing (with the trap system) and farming the bluefin tuna entering the St. Margaret Bay (Nova Scotia).

Production was quite high in the period 1973-1978 – a maximum of 948 tonnes was achieved in 1977; however, only 72 specimens were captured in 1979. In 1980-1982 127 tuna were produced but in 1983 only 17. From 1984 captures were close to zero. Production started again in 1993 with 29 tonnes, and increased to 78 tonnes in 1994 (Table 45). The importance of an accurate knowledge of the ethology of the species is fully demonstrated by the Canadian fishing practice for capture-based aquaculture. Following some years of commercial success, a sudden change in the migratory pattern of northern bluefin tuna, due to hydrological changes in the warm current flowing into the Bay, led to the closing down of the business.

Table 45. Production of capture-based tuna aquaculture in Canada

Year Average production (tonnes/year)
1964-1972 401
1973-1978 630
1984-1990 0
1993 29
1994 78