12 
Fishery Bulletin 95( 1 ), 1997 
The archeological evidence and ethnohistoric ac- 
counts are significant because of the absence of mod- 
ern records for adult bluefin tuna in the northeast- 
ern Pacific. Consequently, the distribution of north- 
ern bluefin tuna of all age classes in the Pacific and 
all modern records for adults in the eastern Pacific 
are reviewed. The addition of historical information 
presented here to our present state of knowledge of 
modern bluefin tuna distributions has important 
implications for our understanding of changing en- 
vironmental conditions over time and perhaps also 
for determining the impact of 20th-century fisheries 
on Pacific bluefin tuna populations. 
Distribution of Pacific bluefin tuna 
The distribution of northern bluefin tuna in the Pa- 
cific is somewhat enigmatic, especially that of the 
adult portion of the population (Foreman and 
Ishizuka, 1990; Bayliff, 1994; Smith et al., 1994). 
Sexual maturity in Pacific northern bluefin is 
reached at about 5 years, and most spawning is re- 
ported between April and July in waters off Japan 
and the Philippine Islands, and in August in the Sea 
of Japan (Bayliff, 1994). Northern bluefin tuna are 
transoceanic migrators in both the Atlantic and Pa- 
cific; the movements of these fish are largely deduced 
by tagging experiments and catches of various age 
classes at specific times and locations (Nakamura, 
1969; Rivas, 1978; Bayliff, 1994). 
Some of the population of Pacific bluefin tuna mi- 
grate from the western to the eastern Pacific Ocean 
during their first or second year. The proportion of 
the population that undertakes this migration ap- 
pears to vary from year to year (Bayliff et al., 1991). 
These migrating fish spend a period of one to six years 
in the eastern Pacific, a sojourn which may or may 
not be interrupted by visits to the central or western 
Pacific before the survivors return to spawn in the 
west (Bayliff, 1994). Adult fish in the Pacific appear 
to follow a general pattern of being distributed far- 
ther to the west during the spring (when spawning 
occurs) and farther to the east in the fall (Bayliff, 
1993). 
It is not known if all fish return to spawn every 
year after sexual maturity is reached. Tagging ex- 
periments indicate that although the journey from 
west to east may take 7 months or less, the journey 
from east to west takes nearly 2 years; therefore there 
does not appear to be enough time for mature adult 
fish migrating from the eastern Pacific to spawn in 
the west every year. In addition, because a few adult 
fish have been captured in the eastern Pacific either 
just before or after the spawning season, some adults 
probably do not return to the western Pacific every 
year but rather spend variable lengths of time in the 
eastern Pacific (Bayliff, 1994). 
Most harvested adult bluefin tuna are caught in 
the western Pacific, where they are known to range 
as far north as the Sea of Okhotsk at about 50°N 
(Bayliff, 1980). Catch records of large bluefin tuna 
are noted at feeding areas off northeastern Honshu, 
Japan (ca. 40°N), off eastern Taiwan (about 25°N), 
and in the central Pacific near the Emperor Sea- 
mount (40°N, 175°E) (Nakamura, 1969). 
Adult bluefin tuna are considered rare everywhere 
in the eastern Pacific; sporadic records have come 
from southern California and northern Mexico only. 
Although small bluefin tuna (less than 120 cm total 
length [TL] and 5—45 kg) are caught regularly off 
California and Mexico and somewhat larger fish 
(120-160 cm TL and 45-80 kg) occasionally, adults 
over 160 cm TL (80 kg) are seldom encountered (Fore- 
man and Ishizuka, 1990; Bayliff, 1994). 
In the northern portion of the eastern Pacific, few 
modern records exist for bluefin tuna. Neave (1959) 
mentioned three occurrences in British Columbia 
waters during August 1957 and 1958, but no sizes or 
numbers were given. These reports came from an 
area approximately 200-400 miles off the west coast 
of Vancouver Island (49°N, 134°24'W; 48°N, 131°06'W; 
51°N, 130°W). A 7.5-kg bluefin tuna was caught in a 
salmon seine in July 1958, near Kodiak, Alaska, and 
on 1 October 1957, bluefin tuna were sighted 80- 
100 miles off Cape Flattery, Washington (Radovich, 
1961). Sea-surface temperatures off the British Co- 
lumbia coast were reported as being warmer than 
usual during both years. 
I presume (because no sizes are mentioned in the 
reports) that these recent northern records are for 
relatively small fish of 5-45 kg because this size 
range is the most common in the eastern Pacific. 
Bluefin tuna larger than 45 kg in the eastern Pacific 
are rare enough that they are noteworthy when en- 
countered. Although the earliest modern record of a 
very large bluefin tuna in southern California ap- 
pears to be that of 1899 (Holder, 1913), sporadic oc- 
currences of bluefin tuna over 50 kg have been re- 
ported since then (Dotson and Graves, 1984; Fore- 
man and Ishizuka, 1990). 
The largest reported catch of giant bluefin tuna in 
the eastern Pacific was made in 1988 (Foreman and 
Ishizuka, 1990). Seiners caught an estimated 987 
adult bluefin tuna between November and early 
January off southern California, including many over 
100 kg and some more than 250 kg, including one 
that broke California records at 458 kg and 271.2 
cm TL. Seiner operators involved in this fishery re- 
ported that large bluefin tuna travelled in small 
