Southwest Fisheries Science Center
National Marine Fisheries Service, NOAA
La Jolla, California 92038
Terry J. Foreman
Inter-American Tropical Tuna Commission
La Jolla, California 92038
North Pacific albacore have been fished off Japan and North America since at least the turn of the century. These early fisheries were mostly coastal in nature, extending only a few hundred miles offshore. By the early 1950s the longline fishery for albacore extended across the Pacific. Total catches from 1952 to 1960 ranged from 51,000 mt to 94,000 mt. Prices paid (and world demand) for albacore are and have been considerably higher (as much as 2 or 2 ½ times) than the price paid for tropical tunas used for canning. The albacore is therefore a highly desirable species world-wide.
The North Pacific albacore is the same species as albacore found elsewhere. Specifically, from the suborder level the taxonomy is:
Bonnaterre is credited with the current scientific name.
3. EARLY LIFE HISTORY
Descriptions of larval-phase albacore are found in Matsumoto (1962), Matsumoto et al., (1972), and other literature.
Juvenile albacore are found in tropical and subtropical waters of the North Pacific. Although most documented findings of very small (12–400 mm) juveniles are from the South Pacific, fish in this size range have been found around Hawaii (Yabe et al., 1958; Yoshida, 1965; and Yoshida, 1968) and in the eastern Pacific near Guadalupe Island (Clemens, 1961).
Small albacore, presumably smaller than 25 cm have been caught in the eastern Pacific in some years. Small albacore (28 – 35 cm) are commonly found in considerable abundance in Japanese coastal waters in spring and summer, with considerable year-to-year variation (Nakamura, 1969).
4. AGE AND GROWTH
Considerable efforts have been applied to estimating age and growth from hard parts, size composition data and tagging experiments. Foreman (1980) presents a summary of age and growth parameters which shows considerable differences between authors. Laurs et al. (1985) found a linear relationship of 0.954 rings per day between detectable otolith-increment counts and days at liberty following tagging and tetracycline injection for fish between 50 and 100 cm. From subsequent (unpublished) whole-otolith, total-ring counts as well as unpublished data from a similar study by one of the authors (Bartoo) it appears that North Pacific albacore have approximately the following size at age: 1 – 35 cm, 2 – 52 cm, 3 – 65 cm, 4 – 76 cm, 5 – 85 cm, 6 – 93 cm. Laurs and Wetherall (1979) demonstrated from tagging data that fish captured south of 40°N had a higher estimated growth rate than fish captured north of 40°N. Yoshida (1968) estimates that juveniles grow at a rate of 3.19 cm per month, which is fairly consistent with the above information.
The von Bertalanffy parameters, L∞ = 135.6 cm, K=0.17, to = -0.87, fit the sizes at age reasonably well and appear reasonable to use for assessment purposes.
Weight at size estimated from the equation w (kg) = 2.188 × 10-5 L2.99(mm) has been empirically tabulated by Clemens (1961) for sizes between 38 and 100 cm (Table 1). As this relationship was based on fish taken in the North American troll fishery, it is reasonable to assume variability between areas and seasons. A summary of length-weight relationships from various fisheries appears in Foreman (1980).
5. MATURATION AND SPAWNING
North Pacific albacore mature at approximately 5 years of age, or about 85 cm (Ueyanagi, 1957; Otsu and Uchida, 1963). Fecundity is estimated to be 0.8 to 2.6 million eggs per spawning (Ueyanagi, 1957; Otsu and Uchida, 1959). Peak spawning occurs in subtropical waters from March through July (Foreman, 1980). There is evidence that other tuna species spawn repeatedly throughout their spawning period and evidence for multiple spawning has been found in albacore (Otsu and Uchida, 1959), although no estimates of the spawning frequency exists. Few collections of running ripe fish have been made. Immature albacore (<80 cm) generally have a sex ratio of 1:1, but males predominate in catches of mature fish (Otsu and Uchida, 1959). The sex ratio may vary between years.
6. STOCK STRUCTURE, DISTRIBUTION, AND MIGRATION
The migration of North Pacific albacore has been described by several authors (Clemens, 1961; Otsu and Uchida, 1963; Laurs and Lynn, 1977). In general, the bulk of the juvenile albacore recruiting into the North Pacific fisheries first enters the Japanese western Pacific fisheries off Japan and then moves eastward. Recovery of tagged juveniles (ages 1 to 5) indicates that fish tagged off Japan appear in the North American fishery; movement is along the North Pacific Transition Zone. Albacore tagged off North America seem to move across the Pacific during the fall and appear in the Japanese late-winter/spring fisheries near Japan. These fish then appear to migrate back to North America. There are few tag returns of mature fish. Based on catch patterns it would seem that adults move to lower latitudes. In addition to this general pattern of movement there may be variations associated with recruitment. It appears that a small portion of the population may spawn further east than the bulk of the population and first enter the fishery off North America (see summary in Foreman, 1980).
Table 1. Relationship between albacore fork length and weight (from Clemens, 1961).
|Fork Length (mm)||Weight (lbs.)||Fork Length (in.)|
7. OCEANOGRAPHIC FEATURES ASSOCIATED WITH THE SPECIES
Water temperature affects albacore distribution (Clemens, 1961). Albacore catches are generally associated with sea-surface temperatures between 15.0°C and 19.4°C, although telemetry experiments have documented that albacore may move vertically into much colder waters for short periods of time. Smaller fish tend to be found in cooler waters (Clemens, 1961).
Albacore concentrate along oceanic fronts (thermal discontinuities) and thus their fisheries extend Pacific-wide (Laurs and Lynn, 1977). Food concentration appears to be the key mechanism (Sund, et al., 1981).
8. INTERACTION WITH OTHER SPECIES
Recent drift gillnet surveys in the North Pacific indicate that albacore are often found in the same area as pomfret (Brama spp.) and blue sharks (Prionace glauca). There appears to be no direct species interactions (i.e. associations) between albacore and other fish species, although albacore may associate with drifting masses of giant kelp in the eastern Pacific and are sometimes caught mixed with other tunas.
9. GENERAL DESCRIPTION OF FISHERIES
In the North Pacific, albacore are caught in significant quantities by both surface and subsurface gears.
Longline fisheries (the only ones to use subsurface gear) are operated primarily by Japan (95% of the total catch) and to a lesser extent by Taiwan and Korea. Figure 1 shows the general distribution of the longline fisheries. Longline catches have averaged near 15,000 mt over the last 10 years (Table 2).
Major surface fisheries taking significant amounts of North Pacific albacore include the North American troll fishery, the Japanese pole-and-line (baitboat) fishery, the Taiwanese and Japanese large-mesh drift gillnet fishery, and the Japanese, Taiwanese and Korean small-mesh squid drift gillnet fishery (Figure 1). Catches from the troll and pole-and-line fisheries (Table 2) have shown a marked decline over the last 10 or 15 years, while drift gillnet catches have increased (Table 2) since 1980 (although data are incomplete for this segment of the fishery).
Figure 1. General distribution of albacore showing distribution of major surface and longline fisheries.
|Korea||USA||Canada Troll||Grand total|
|Pole & line||Longline||Driftnet||Purse seine||Others||Sub total||Longline||Driftnet||Sub total||Longline||Driftnet||Pole & line||Troll||Driftnet||Purse seine||Sport||Sub total|
The following notes apply to this table:
Table 2. Catch of North Pacific albacore by gear, 1952–1990.
10. TRENDS IN EFFORT, CATCH, AND CATCH-PER-UNIT-EFFORT
The longline fishery is best indexed by the Japanese fleet. The Japanese longline fleet has a directed fall-winter fishery for adult albacore although a small proportion of immature fish are taken in some areas. The reduction in catches in the very early 1970s (Table 2) reflects a shift in fishing effort toward bigeye tuna (Sakagawa et al., 1987). After this change the longline catch of albacore stabilized (Figure 2).
Figure 2. Japanese fleet longline catch in weight (upper panel) and numbers (lower panel).
Effective effort (Figure 3) has shown great fluctuations during the period associated with the change in fishing operations. After 1975 effective effort increased approximately 24%, with modest fluctuations.
Catch-per-unit-effort (CPUE) in numbers of fish-per-hook has shown a slight down trend from the mid-1970s through 1985 (Figure 4). The CPUE in 1986 was down about 40% from the recent years CPUE average. The CPUE as measured by kg-per-100 effective hooks (Figure 4) showed an erratic trend through 1975 associated with fishery changes. Since 1975 this CPUE index has been relatively stable, declining slightly in the most recent years.
The average weight per fish captured as calculated from total tonnage and total numbers estimated in the catch remained relatively constant through the late 1960s (Figure 5). From 1969 through 1974 (the period of operations change) the average weight increased steadily, and from 1975 through 1986 the average weight remained relatively constant. In 1986 the average weight increased.
Figure 3. Estimated effective-effort for albacore by the Japanese longline fleet.
10.2 Pole and Line
The pole-and-line (baitboat) fishery is almost exclusively Japanese. The vessels fishing albacore are predominantly 100 gross tons or larger and are part of a multi-species fishery. These vessels fish for skipjack tuna most of the year and as albacore become available, shift to albacore. The fishery for albacore generally begins south of the Japanese home islands in March or April and moves northward and east along the Kuroshio extension waters.
Figure 4. Estimated catch-per-unit-effort for the Japanese longline fleet in weight per 100 hooks (upper panel) and numbers per 100 hooks (lower panel).
Figure 5. Estimated average weight per fish in the Japanese longline fishery.
Catches for the pole-and-line fleet are shown in Table 2. Peak catches of 70,000 to 85,000 mt were seen in the mid-1970's, but have dropped rather steadily to just over 6,000 mt in 1988. Korea reportedly has had a small live-bait fishery for albacore since the 1960s, although no official statistics are available.
Information on effort in the pole-and-line fishery is available for Japanese boats which exceed 100 gross tons and have licenses to operate over the 1961 to 1987 period (Figure 6). Note that the peak number of boats corresponds to the timing of the peak catches. Recent declines in vessel numbers are due in part to conversion of vessel licenses from pole-and-line to purse seine and reduced economic viability of the fishery.
The CPUE for the pole-and-line fleet (Figure 7), is relatively constant until 1976 when it declined considerably. Since 1976 it appears to have been increasing, although during this period improvements in efficiency may have biased the actual trend upward (see discussion on USA troll fleet below). The effort used in the calculations does not include days with effort and zero catch even if the vessel was searching for fish, due to the way data are reported. Average CPUE per day per boat (mt/day/boat; Figure 8) shows a relation between the number of boats and CPUE. During the period when many boats were in the fleet (the period of peak catches also), CPUE was lower than during the period before and after.
Figure 6. Number of pole-and-line boats larger than 100 gross tons licensed to fish albacore.
Figure 7. Estimated catch-per-unit-effort for albacore in the Japanese pole-and-line fleet.
Figure 8. Number of pole-and-line boats larger than 100 gross tons licensed to fish albacore.
The North American troll (jig) fishery is predominantly conducted by USA vessels with a few Canadian vessels. The troll vessels are generally coastal boats averaging 18 m in length, with a maximum size of about 26 m. The fishery begins with larger vessels fishing north of Midway Island in the north-central Pacific in May or June and proceeds eastward toward North America. Smaller boats from coastal bases of the USA begin fishing 200 to 1,000 miles offshore in late July. The fishery moves along the coast of the USA and Canada following the movement of albacore.
Statistics on the troll fishery (Table 2) show a period of high catches between 1959 to 1975 (nearly 20,000 mt in most years) with catches declining to a low of less than 2,000 mt in 1989. Effort in the fishery (Figure 9) estimated from total landings and CPUE, generally increased through the mid-1970s. Effort then began to decline steeply to current levels of about 20% of the average level in the mid-1970s. There is considerable year-to-year variation in effort, due in part to alternative fisheries such as the salmon troll fishery.
The CPUE for the USA fishery measured in numbers of fish-per-days-fishing (Figure 10) shows a continuous decline from the mid-1960s to the present, with year-to-year fluctuations of up to 30%. The CPUE as measured in metric tons per day per boat (Figure 11) is almost identical in trend to CPUE measured in numbers of fish.
The average weight per fish taken in the North American fishery showed no trend in the 1960s and 1970s (Figure 12). In 1979 and 1980 the average size increased considerably but dropped below the long term average in 1981 and, with the exception of a few years, has since been decreasing.
Figure 9. Estimated effort in the USA troll fishery.
Figure 10. Estimated catch-per-unit-effort in numbers per day for the USA troll fleet.
Figure 11. Estimated catch-per-unit-effort in metric tons per day per boat for the USA troll fleet.
Figure 12. Estimated average weight per fish in the USA troll fishery.
10.4 Drift Gillnet
Albacore catches for the drift gillnet fisheries, both large-mesh and squid, are shown in Table 2 and are incomplete for Taiwan and Korea. Catches by the Japanese drift gillnet fishery began in 1972 and remained relatively small until 1981 when effort expanded. From 1981 to 1989 catches were in the 6,000 to 12,000 mt range. Taiwan's catch is reported only for 1987 – 1989 and ranges from 4,000 mt to 11,000 mt. None of the reported catches include estimates of non-landed catches which may have been lost or discarded at sea.
There are no reliable estimates of total effort or CPUE for the drift gillnet fleets. The total number of large-mesh drift gillnet vessels fishing in 1990 is estimated at 160.
11. POPULATION DYNAMICS
The condition of the North Pacific albacore stock was reviewed at the 12th North Pacific Albacore Workshop in 1991. The following is based on the findings of the workshop which considered additional information than that presented here.
Firstly, no discussion was held concerning maximum sustainable yield (MSY). The 11th albacore workshop concluded that no reliable estimate of MSY is available; previous MSY estimates in the range of 90,000 mt to 200,000 mt may be suspect because of the different CPUEs used for the USA fleet and the pole-and-line fleet and the possibility of changes in the age structure of the catch over time.
Secondly, the changes in abundance of the population of young albacore are best indicated by data from the troll and pole-and-line fisheries. The trend in adult abundance is best represented by the Japanese longline. It appears that the adult stock has been relatively stable during the 1966 to 1986 period. Since 1986 the trend has been downward, declining as much as 30%. The trend in young fish abundance since 1977 is relatively stable but at a level 1/3 lower than before 1977. The pole-and-line CPUE trend from the mid-1970s to the present (see above) is thought to be biased upward and the actual trend is likely to be level.
The conclusion reached on the condition of the stock is that the North Pacific albacore stock is producing at a lower yield level than in the mid-1970s. The unreported drift gillnet catches, which may be substantial, make it difficult to estimate exactly how much lower production is, but it is down by at least 1/3. The adult portion of the stock appears to be in stable condition.
The unreported catches in the 1980s and the unknown but possibly high mortalities from non-landed catches in the drift gillnet fisheries, make the stock status uncertain and in need of monitoring. It is expected that additional data will be available in 1992 or 1993.
There is considerable evidence that fisheries in the North Pacific catching albacore interact with each other. Tag data show that albacore taken off North America are available to the pole-and-line fishery off Japan and vice versa. Further, albacore tagged in surface fisheries have been recovered in the longline fishery.
There are data showing that albacore encountering drift gillnets and escaping are taken in the same and succeeding seasons in the troll fishery (Bartoo et al., 1991). Observations made during the troll-fishing season showed fresh net marks and wounds were present on an average of 7.2% of the fish caught by U.S. trollers. Old scars, presumably from a previous fishing season, were found on 5.2% of the troll-caught fish, bringing the total proportion of the troll catch bearing “tags” from the drift gillnet fisheries to 12.4%. There are no similar data reported for the pole-and-line fishery.
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