244 
Abstract — The Pacific Rim population 
structure of chum salmon ( Oncorhyn - 
chus keta) was examined with a 
survey of microsatellite variation to 
describe the distribution of genetic 
variation and to evaluate whether 
chum salmon may have originated 
from two or more glacial refuges fol- 
lowing dispersal to newly available 
habitat after glacial retreat. Variation 
at 14 microsatellite loci was surveyed 
for over 53,000 chum salmon sampled 
from over 380 localities ranging from 
Korea through Washington State. An 
index of genetic differentiation, F ST , 
over all populations and loci was 
0.033, with individual locus values 
ranging from 0.009 to 0.104. The 
most genetically diverse chum salmon 
were observed from Asia, particularly 
Japan, whereas chum salmon from 
the Skeena River and Queen Char- 
lotte Islands in northern British 
Columbia and those from Washington 
State displayed the fewest number of 
alleles compared with chum salmon 
in other regions. Differentiation 
in chum salmon allele frequencies 
among regions and populations within 
regions was approximately 18 times 
greater than that of annual varia- 
tion within populations. A regional 
structuring of populations was the 
general pattern observed, with chum 
salmon spawning in different tribu- 
taries within a major river drainage 
or spawning in smaller rivers in a geo- 
graphic area generally more similar 
to each other than to populations in 
different major river drainages or geo- 
graphic areas. Population structure of 
chum salmon on a Pacific Rim basis 
supports the concept of a minimum 
of two refuges, northern and south- 
ern, during the last glaciation, but 
four possible refuges fit better the 
observed distribution of genetic varia- 
tion. The distribution of microsatellite 
variation of chum salmon on a Pacific 
Rim basis likely reflects the origins of 
salmon radiating from refuges after 
the last glaciation period. 
Manuscript submitted 28 August 2008. 
Manuscript accepted 22 January 2009. 
Fish. Bull. 107:244-260 (2009). 
The views and opinions expressed 
or implied in this article are those 
of the author and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Population structure of chum salmon 
( Oncorhynchus keta) across the Pacific Rim, 
determined from microsatellite analysis 
Terry D. Beacham (contact author) 
John R. Candy 
Khai D. Le 
Michael Wetklo 
Email address for contact author: Terry.Beacham@dfo-mpo.gc.ca 
Fisheries and Oceans Canada, 
Pacific Biological Station, 
3190 Hammond Bay Road 
Nanaimo, B. C., Canada V9T 6N7 
Delineation of phylogenetically and 
adaptively distinct groups in the dis- 
tribution of chum salmon around the 
Pacific Rim may lead to conserva- 
tion of genetic diversity through an 
understanding of the origin and the 
evolutionary processes promoting and 
maintaining genetic differentiation. 
An evaluation of genetic variation in 
describing the population structure 
of salmonids, is a key component in 
the elucidation of management units 
or conservation units in a species and 
can be applied to manage fisheries 
exploiting specific stocks of salmon. 
Several methods of surveying genetic 
variation have been used to investi- 
gate regional and Pacific Rim varia- 
tion in chum salmon ( Oncorhynchus 
keta Walbaum). Allozymes have been 
used for a number of years to describe 
chum salmon population differentia- 
tion and structure (Okazaki, 1982a; 
Kijima and Fujio, 1982; Wilmot et ah, 
1994; Efremov, 2001; Salmenkova et 
al., 2007). Variation in mitochondrial 
(mt) DNA has also been investigated 
(Park et ah, 1993; Sato et al., 2001, 
2004), as has minisatellite variation 
(Taylor et al., 1994; Beacham, 1996). 
Non-mtDNA single nucleotide polymor- 
phisms have been examined (Smith 
and Seeb, 2008), as have microsat- 
ellites (Chen et al. 2005; Beacham 
et al. 2008a, 2008b, 2008c, 2009). 
Microsatellites are useful for evalu- 
ating fine-scale population structure 
in salmonids (Banks et al., 2000), and 
for investigating population structure 
around the Pacific Rim (Beacham et 
ah, 2006a, 2006b). 
Chum salmon display one of the 
widest spawning distributions of Pa- 
cific salmon. In Asia, chum salmon 
are distributed from Korea and Ja- 
pan in the south to the Arctic Ocean 
coast of Russia in the north; in North 
America, the distribution has histori- 
cally ranged from California in the 
south to the Beaufort Sea coast in the 
north, and as far east as the Mack- 
enzie River in the Arctic (Salo, 1991). 
After fry emerge from the gravel nest 
in the spring or are released from 
hatcheries, they generally move di- 
rectly to marine residence, first to 
estuaries, and later in the year to 
nearshore and offshore waters. Most 
individuals reside three to five years 
in the marine environment and then 
undertake spawning migrations gen- 
erally to their natal river beds. 
Chum salmon were likely fairly 
widely distributed along the Pacific 
Rim before the last major glaciation 
(McPhail and Lindsey, 1970). The 
advent of glaciation restricted the 
distribution of chum salmon to some 
major and perhaps minor refuges. 
Existing chum salmon population 
structure has been associated with 
colonization events following the last 
glaciation (Seeb and Crane, 1999). 
Modern populations were thought to 
have originated largely from a Ber- 
ing Sea refuge in the north and a 
Columbia River refuge in the south 
(McPhail and Lindsey, 1970). In Asia, 
