Nichol and Somerton: Seasonal migration of mature males of Chionoecetes opilio in the eastern Bering Sea 
319 
eas where these females resided, including 
9 of the large males (>113 mm CW) that re- 
mained at depths >120 m and did not make a 
dedicated inshore migration. Therefore, they 
all had an opportunity to mate with mul- 
tiparous females. In contrast, opportunities 
to mate with pubescent-primiparous females 
were unlikely given that these females were 
concentrated (Fig. 5) much farther to the 
east (shallower waters) and to the north. The 
two small tagged males that migrated to a 
90-m depth were the exception; however, the 
months during which these males resided at 
a depth of 90 m (June-July), were well past 
the period of pubescent-primiparous mating 
(February-March). 
Summer distributions of morphometrically 
mature and adolescent males 
Small MM males (70-100 mm CW) were 
concentrated farther north and east (shal- 
lower water) of areas where large MM males 
(>100 mm CW) of the same shell condition 
resided, and new-shell MM males were con- 
centrated farther east (shallower) than that 
where older-shell MM males of the same 
size class resided (Fig. 7, A-D). Large older- 
shell MM males were primarily distributed 
over the outer shelf (depths of 100-200 m), 
whereas new-shell MM males, from both 
size classes, were primarily distributed over 
the middle shelf (depths of 50-100 m), at 
least south of 59°N. Adolescent males of 
both size classes were distributed over the 
middle shelf (i.e., south of 59°N), and small 
individuals were distributed more to the 
northeast of areas where large individuals 
were distributed (Fig. 7, E and F). 
Discussion 
Most of the tagged MM males migrated in- 
shore either shortly after their release dur- 
ing spring or during the following winter or 
spring. These migrations were not extensive 
enough to have contributed to the spatial 
difference in distributions between large 
males observed on the middle shelf dur- 
ing the NMFS summer bottom trawl survey and those 
males targeted on the outer shelf during the winter 
fishery. A seasonal shift in distribution of large males 
would be expected because of the fall migration of re- 
cently terminally molted males to deeper water, but 
this shift should be more prominent if these and older- 
shell MM males migrate back inshore every spring. 
Although springtime inshore migrations did occur, all 
but 2 of the tagged males remained on the outer shelf 
(depths >100 m) throughout their time at liberty. 
The summer distribution of large, older-shell MM 
males (Fig. 7D) in waters deeper than 100 m con- 
firmed the supposition that few of these individu- 
als migrated back inshore to the middle shelf. The 
highest concentrations of large males found over the 
middle shelf (depths 50-100 m) during the summer 
survey (Orensanz et al., 2004; Turnock and Rugolo 4 ), 
therefore, likely were not composed of MM males 
that seasonally migrated inshore but of recently ter- 
minally molted MM males that had yet to migrate 
