258 
Fishery Bulletin 107(2) 
two continents (Beacham et al., 2006a, 2006b). This 
is in marked contrast to the pattern observed in chum 
salmon, with Asian chum salmon displaying signifi- 
cantly greater genetic diversity than that observed in 
chum salmon populations in North America. Surveys 
of mtDNA variation have also indicated that Japanese 
populations have the highest genetic diversity among 
Pacific Rim chum salmon (Sato et al., 2004). Chum 
salmon in Asia display a wider geographic distribution 
than either sockeye salmon or Chinook salmon, with 
most populations of these two species restricted to a 
Russian distribution, whereas chum salmon range as 
far south as South Korea. The distinctive nature of 
Korean, Japanese, and Primorye chum salmon, coupled 
with the higher diversity observed in Asian popula- 
tions, indicates an Asian refuge from which chum salm- 
on dispersed after the retreat of glaciers during the 
Pleistocene, either on the southern Asian mainland or 
the islands of Japan. The fact that Asian chum salmon 
display more genetic diversity than North American 
chum salmon reflects either that either higher popula- 
tion sizes were present in this refuge, allowing more 
genetic variation to be retained, or that dispersal from 
this refuge preceded those in North America, allowing 
more time for genetic mutations to accumulate. The 
concept of a glacial refuge near Japan was also sug- 
gested by Taylor et al. (1994). 
In North America, the observed population structure 
of chum salmon would support the concept at a mini- 
mum of a Bering Sea refuge in the north (unglaciated 
areas of western Alaska or Russia) and a Columbia 
River refuge in the south (unglaciated area west of 
the Continental Divide) as suggested by McPhail and 
Lindsey (1970). Present day populations in Korea, Ja- 
pan, and Primorye may be derived from the southern 
Asian (Japanese) refuge, populations from the Amur 
River through to southern Bristol Bay may be derived 
from the northern Bering refuge, and populations from 
the Alaska Peninsula to Washington may have been 
derived from the southern refuge. In British Columbia, 
an additional refuge may also have been present on the 
Queen Charlotte Islands (Warner et al., 1982). Queen 
Charlotte Islands chum salmon populations were dis- 
tinct and also displayed lower genetic variation, very 
similar to sockeye salmon populations from the region 
(Beacham et al., 2006a). Wood (1995) suggested that 
sockeye salmon population structure on the central 
coast region of British Columbia was consistent with 
colonization from two different refugia, and therefore 
it is possible that present day populations in British 
Columbia are derived from chum salmon originating 
from a Queen Charlotte Islands refuge and that other 
portions of the coast were colonized by chum salmon 
that originated from a southern refuge. 
Acknowledgments 
A very substantial effort was undertaken to obtain 
samples from chum salmon sampled in this study. In 
North America, starting from the south, we thank J. B. 
Shaklee, various staff of Fisheries and Oceans Canada 
(DFO) for baseline sample collection, as well as First 
Nations staff, R. L. Wilmot, L. W. Seeb, S. Johnston, 
P. Milligan, J. Wenburg, and A. J. Gharrett. For Asia, 
samples were provided by V. V. Efremov, N. V. Varnaks- 
kaya, G. Winans, S. Urawa, S. Sato, and J. Park. L. 
Fitzpatrick drafted the map. C. Wallace assisted in the 
analysis. Funding for the study was provided by Fisher- 
ies and Oceans, Canada. 
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