525 
Abstract .—We used allozyme 
analyses to investigate genetic varia- 
tion among commercially exploited 
populations of Chionoecetes bairdi 
(Tanner) and C. opilio (snow) crabs in 
Alaskan waters. Data were collected 
from 34 presumptive loci in 1002 C. 
bairdi and 539 C. opilio sampled 
throughout the commercially important 
range of each species in Alaska. Aver- 
age observed heterozygosities were 
0.027 for C. bairdi and 0.013 for C. 
opilio. Low levels of geographic differ- 
entiation were detected among popula- 
tions of C. bairdi and C. opilio , and our 
data suggest that subpopulations of C. 
bairdi exist within the Bering Sea. Fur- 
ther, evidence of gene introgression was 
found between C. bairdi and C. opilio 
in the Bering Sea. We also included a 
geographic isolate, North Atlantic C. 
opilio, in the analyses. Little differen- 
tiation was found, and no private alle- 
les were detected in North Atlantic C. 
opilio despite significant geographic 
separation from Alaskan C. opilio. 
Manuscript accepted 24 October 1997. 
Fishery Bulletin 96:525-537 ( 1998). 
Low levels of genetic diversity in highly 
exploited populations of Alaskan 
Tanner crabs, Chionoecetes bairdi, 
and Alaskan and Atlantic snow crabs, 
C. opilio* 
Susan E. Merkouris 
Lisa W Seeb 
Genetics Laboratory 
Commercial Fisheries Management and Development Division 
Alaska Department of Fish and Game 
333 Raspberry Road, Anchorage, Alaska 995 1 8-1 599 
E-mail address (for S E Merkouris): SueMOfishgame. state. ak. us 
Margaret C. Murphy 
PO. Box 25526 
Juneau, Alaska 99802-5526 
Five species of the genus Chio- 
noecetes , Majidae, are described 
from the North Pacific region 
(Rathbun, 1925; Garth, 1958). The 
nearly circumpolar range of C. 
opilio (snow crab) includes the 
Bering Sea, the Arctic Ocean, the 
western North Pacific coast of Asia, 
and the northern Atlantic Ocean. 
Chionoecetes bairdi , C. angulatus, 
and C. tanneri are widespread in 
the eastern North Pacific (Garth, 
1958). Chionoecetes japonicus is 
found only in the western North Pa- 
cific along the coast of Asia. In the 
Alaskan waters of the Bering Sea, 
the distribution of C. bairdi is 
strongly associated with the conti- 
nental slope areas along the coast 
of the Alaska Peninsula, and the 
Pribilof Islands (Otto, 1982), and 
there is considerable overlap in the 
distribution of C. bairdi and C. 
opilio (Karinen, 1974). 
Commercial fisheries for male C. 
bairdi and C. opilio in Alaska, along 
with king crabs ( Paralithodes and 
Lithodes) have long been the world’s 
most abundant sources of crabs and 
have considerable current and his- 
torical commercial importance in 
Alaska (Otto, 1990). Chionoecetes 
bairdi are faster growing, larger, 
and more valuable than C. opilio. 
Commercial harvests of C. bairdi in 
the Bering Sea and Gulf of Alaska 
fisheries peaked in the late 1970s, 
declined throughout the 1980s, and 
although some populations of C. 
bairdi have recently rebounded, 
many fisheries remain closed owing 
to low abundance (Kruse, 1993). 
Rapid development of the Bering 
Sea C. opilio fishery coincided with 
the decline of C. bairdi fisheries, 
and although C. opilio have domi- 
nated landings of Bering Sea crabs 
since the mid-1980s, catches have 
also declined dramatically in recent 
years (ADF&G, 1994). 
Declining abundances of Bering 
Sea and Gulf of Alaska crab popu- 
lations have intensified competition 
for the remaining resources and 
have lead to re-evaluation of crab 
fishery management practices. Gen- 
* Contribution number PP-123 of the Alaska 
Department of Fish and Game, Commer- 
cial Fisheries Management and Develop- 
ment Division, Juneau, Alaska. 
