Institute of Oceanography
National Taiwan University
The catch of yellowfin tuna by Taiwan's pelagic fisheries are briefly described in this report. Traditionally, longline gear was the principal gear used to harvest yellowfin; landings in the early 1970s reached a peak of nearly 10,000 mt. Development of the purse-seine fishery began in early 1980s and by 1990 the yellowfin catch exceeded 12,000 mt. In recent years there has been a dramatic shift in base ports and fishing grounds for the inshore longliners, to more distant waters.
Catch statistics of Taiwan are divided into far-seas, inshore, and coastal fisheries. The far-seas fisheries include vessels larger than 50 gross registered tons (GRT), inshore fisheries include all of the power crafts smaller than 50 GRT, and coastal fisheries include nonpowered craft, set net, beach seine, and inland water fisheries.1
The Taiwanese catch of yellowfin tuna by all types of gear and from all oceans for the period 1964 to 1990 is given in Table 1. The peak catch occurred in 1990 with a catch of 44,513 metric tons (mt). The far-seas fisheries of the Pacific landed approximately 40% of the total Taiwanese yellowfin catch in 1990 (Table 2).
Yellowfin tuna stocks are mainly exploited by tuna longliners, primarily the powered longliners larger than 20 GRT. Only a few yellowfin are caught by other fishing gear such as small gillnet, trolling, and miscellaneous types of longline.
1 From 1990 the definitions for the fisheries were changed to: (a) Far-seas Fisheries -- operating outside of Exclusive Economic Zone (EEZ), (b) Inshore Fisheries -- operating 12 to 200 miles, and (c) Coastal Fisheries -- operating from the coast to 12 miles.
2. FAR-SEAS FISHERIES
Longline and purse seine are the two most important types of fishing gear used in exploiting yellowfin stocks.
In the Pacific the Taiwanese far-seas longliners mainly fish in the South Pacific (Wang, 1988). The target species of this fishery is albacore. Most of the longliners are of 100–500 GRT (Table 3). In 1977 the total number of far-seas longliners operating in the South Pacific was 178; the number decreased to a low of 44 in 1985 and subsequently increased to 96 in 1990. The fluctuations in vessel numbers reflect a shift in fishing area and not a change in fleet size.
Table 1. Total Taiwanese yellowfin tuna catch, 1964–1990.
Sources: Taiwan Fisheries Bureau (TFB) annual reports, 1965–1991; Tuna Research Center (TRC) annual reports, 1973–1991.
The peak longline catch in the Pacific occurred in 1972 when the catch was about 10,000 mt (Table 2). Subsequently, the catch declined steadily, reaching a low of 862 mt in 1983. Since 1983 the catch has fluctuated slightly. It reached a post-1983 high of 5,411 mt in 1990.
The catch composition of the Taiwanese far-seas longline fishery for 1970, 1980, and 1990 is given in Table 4. Albacore made up 37%, 47%, and 38% of the catch for 1970, 1980, and 1990, respectively, indicating that it is the target species. Since yellowfin made up a smaller share of the catch, with 32%, 8%, and 12% for the years 1970, 1980, and 1990, it is clearly not the species targeted by Taiwanese far-seas longliners.
2.2 Purse Seine
The catch of yellowfin by the Taiwanese purse-seine fishery was first reported in 1982 (Table 2). The purse-seine catch of yellowfin increased from 298 mt in 1982 to 14,540 mt in 1990. Although details of the catch by oceans are not available, it is estimated that more than 80% of the catch was made in the Pacific. In 1990 Taiwanese purse seiners numbered 44. In the Pacific they fished mainly in waters around Micronesia.
Table 2. Yellowfin tuna catch of Taiwanese far-seas fisheries, 1964–1990
|Year||All Oceans||Pacific Ocean|
Sources: Taiwan Fisheries Bureau (TFB) annual reports, 1965–1991. Tuna Research Center (TRC) annual reports, 1973–1991.
Legend: LL -- Far-seas tuna longliners (1967–1979 data based on logbooks, 1980–1990 data provided by TFB), PS -- Purse seiners (data prior to 1989 based on assumption Pacific PS/All Oceans PS equal to that of 1989); GN -- Gill netters (data prior to 1989 based on assumption Pacific GN/Far-seas GN equal to that of 1989).
Table 3. Number of Taiwanese far-seas tuna longline vessels in the Pacific Ocean (> 50 GRT), 1977–1990.
|Year||Vessel Class (GRT)|
Source: Data provided by Taiwan Fisheries Bureau (TFB) and Tuna Research Center (TRC).
Table 4. Catch composition of Taiwanese far-seas longline fishery, 1970, 1980, and 1990.
Source: Taiwan Fisheries Bureau (TFB) annual reports, 1971, 1981, and 1991.
3. INSHORE FISHERIES
The catch of yellowfin tuna by the various inshore fisheries is given in Table 5. Among the several inshore fisheries the dominant gear for yellowfin is the tuna longline. The yellowfin longline catch increased dramatically from a low of 3,323 mt in 1972 to a high of 22,629 mt in 1979. Much of this increase can be attributed to an increase in effort, as the number of inshore tuna longline vessels during this period increased from 899 to 1,840 vessels (Table 5). The decline in catch since 1979 cannot be easily explained, since fishing effort continued to increase until 1987, when a high of 2,207 vessels was reported (Table 6). It is possible that the decline may reflect discrepancies in reporting and processing of catch statistics. In recent years some of the Taiwanese fishing vessels have based their operations in Singapore, Guam, Palau, and Indonesia. It is conceivable that the catches of these vessels were not reflected in the Taiwanese catch statistics.
Other inshore fisheries are not very important in exploiting yellowfin stocks (Table 5). Target species for the trolling vessels include bonitos and small tunas (less than 50 cm fork length). In 1989 about 15,000 mt of young tuna (including longtail tuna, small yellowfin, and small bigeye) were landed in Taiwan. The reason for the remarkably high catches of the inshore miscellaneous longline fishery in 1987 and 1988 and the drag-net fishery in 1976 is not clear. These unexpectedly high catches may be errors in data recording and processing or the result of changes in fishing gear. In Taiwan, fishing vessels change their gear depending on the season and the species targeted.
3.1 Fishing Effort of Inshore Fisheries
The vessel composition of the Taiwanese inshore fisheries for the period 1964 to 1990 is given in Table 6. With the exception of a recent decline in fleet size of the inshore tuna longline fleet, the general trend for the several fleets of the inshore fisheries has been an increase in number and an increase in average capacity. In 1990 the vessel capacity of the inshore tuna longliners, miscellaneous longliners, and the troll vessels averaged 33, 16, and 8 GRT, respectively.
3.2 Shift of Base Port and Fishing Grounds of Inshore Fishery
A survey carried out from July 1981 to June 1982 (Sun and Yang, 1983) showed that the main fishing grounds for the Taiwan fishery were close to both sides of the Philippine archipelago. Seasonal changes of fishing grounds were very clear. From January to April most of the fishing took place on the western side. From April to June the fishing fleet shifted to the eastern waters of the Philippines and from July to September most of the vessels were operating on the eastern side. From October to December the vessels shifted to the south sector and fished close to the equator.
In 1985 the inshore tuna longliners began seeking new fishing grounds away from Taiwan (personal communication with staff of Tongkang Fisheries Association and captains of fishing vessels). Larger vessels, mainly those larger than 20 GRT, began to use Singapore, Guam, Palau, and Indonesia as bases to land their catch and to obtain necessary supplies. Details of this foreign-based inshore tuna longliner operation in the western Pacific Ocean are not currently available.
The reason for the shift in base ports and fishing grounds is not clear. The shift may reflect exhaustion of traditional fishing grounds or may be the result of the rapid growth in power and capacity of the fishing vessels.
Table 5. Yellowfin tuna catch of Taiwanese inshore fisheries, by gear (1964–1990).
Data source: Adapted from TFB annual reports, 1965–1991.
Legend: ILL = Inshore tuna longline fishery; ML = Inshore miscellaneous fish longline fishery; ITR = Inshore troll fishery; IOT = Other inshore fisheries.
Table 6. Number of Taiwanese inshore tuna fishing vessels, 1964–1990.
|Year||Tuna Longline||Misc. Longline||Troll Line||Total No.|
Source: Taiwan Fisheries Bureau (TFB) annual reports, 1965–1991.
4. COASTAL FISHERIES
The yellowfin catch by Taiwanese coastal fisheries is very small and contributes little to the total Taiwanese tuna catch (Table 7).
Table 7. Yellowfin tuna catch of Taiwanese coastal fisheries, by gear (1964–1990).
Source: Taiwan Fisheries Bureau (TFB) annual reports, 1964–1990
Legend: CST = Coastal set net fishery; CGN = Coastal gillnet fishery; CPL = Coastal pole-and-line fishery; COT = Other coastal fisheries.
Prior to 1987, research of western Pacific yellowfin stock was carried out by the Tuna Research Center (Yang et al., 1970a, 1970b; Wang and Yang, 1970; Yang, 1971; Chen and Yang, 1973; Huang and Yang, 1974; Sun and Yang, 1983; and Wang, 1986). In 1991 two new projects were established. One project involves collecting basic catch and effort data of the Taiwanese inshore tuna longline fishery and the other project involves age determination of southwestern Pacific yellowfin stocks. We expect to obtain more information of yellowfin stocks from these two projects.
6. REFERENCES CITED
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