Nichol and Somerton: Seasonal migration of mature males of Chionoecetes opilio in the eastern Bering Sea 
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Figure 6 
Relationship between the extent of inshore migrations and carapace 
widths of tagged morphometrically mature snow crabs (Chionoecetes 
opilio) released in the eastern Bering Sea in 2010 and 2011 (n= 33). 
Inshore migration extent is defined as the minimum depth (y-axis) 
recorded while a tagged male was at liberty. Numbers next to the 
symbols indicate the month during which tagged males reached their 
minimum depth. 
offshore (Fig. 7B), as well as adolescent 
(small-clawed) males (Fig. 7F). 
Regardless of the extent of inshore mi- 
grations among tagged MM males, most 
males traversed depths at which multip- 
arous females resided, therefore, creating 
the potential for multiparous mating. As- 
suming that observed multiparous sum- 
mer distributions do not differ significant- 
ly from their distributions during spring, 
when most of the multiparous mating 
occurs (Rugolo 2 ), we conclude that there 
was broad spatial overlap between large 
MM males and multiparous females over 
the outer shelf during the mating period. 
In contrast, it is highly unlikely that pu- 
bescent-primiparous females mated with 
large older-shell MM males because of 
the lack of spatial overlap. Even for the 
2 small tagged males that migrated to a 
depth of 90 m, a cross-shelf distance of 
approximately 100 km, the period when 
they occupied the shallowest waters oc- 
curred well after pubescent-primiparous 
mating (February-March; Ernst et ah, 
2005). 
The reasons why 2 of the small tagged 
males migrated such long distances are 
debatable, particularly if a reason is 
related to mating because these males 
reached their shallowest water depth 
during June and July when multiparous mating is al- 
most over. Still, an argument can be made that, because 
some multiparous females were still in a receptive con- 
dition during June and July (Chilton et ah, 2011), the 
small tagged MM males underwent more extensive 
inshore migrations to breed with these females and 
avoid competition from large MM males. The exclusion 
of small MM males by large MM males during mating 
has been observed for snow crabs in waters of eastern 
Canada (Moriyasu and Comeau, 1996; Sainte-Marie et 
ah, 1997; Comeau et ah, 1998) as well as for south- 
ern Tanner crabs in the laboratory (Paul et ah, 1995). 
Lovrich et ah (1995) documented the inshore movement 
of 60-68-mm-CW MM male snow crabs from the Gulf 
of St. Lawrence, and they interpreted this movement 
as a migration of these males early in the season (De- 
cember) in order that they could mate with pubescent- 
primiparous females when there was no competition 
from large MM males. They also reported that some 
intermediate-size (~85 mm CW) MM males migrated 
inshore later in the season (May), the presumption be- 
ing that they would mate with multiparous females 
while benefiting from reduced competition. As reported 
here, Lovrich et ah (1995) found that large MM males 
underwent some inshore movement during spring, but 
generally remained in deeper waters to mate with mul- 
tiparous females. 
A potential extension to this argument is that the 
2 small tagged males engaged in grasping and carry- 
ing behavior (i.e., precopulatory embrace) and carried 
multiparous females from the main multiparous mat- 
ing area to shallower waters, again, to reduce mating 
competition from larger MM males. Paired spring- 
time migrations reportedly occur among snow crabs 
in Bonne Bay, Newfoundland, where MM males carry 
multiparous females from deeper to shallower waters 
(i.e., over a depth range from 150 to 10 m) for mating 
(Taylor et ah, 1985; Hooper, 1986; Ennis et ah, 1990; 
Comeau et ah, 1991). In these studies, the peak of in- 
shore multiparous spawning and mating occurred lat- 
er in the season than the multiparous spawning and 
mating that occurred in deeper waters (Ennis et ah, 
1990), perhaps lending support to the idea of late in- 
shore multiparous spawning and mating in the east- 
ern Bering Sea. 
That the 2 small tagged males in this study were 
among the earliest to migrate inshore (i.e., to make a 
20-m depth change) during the first month after release 
in April, followed by more gradual inshore movement 
into June and July (Fig. 2A), could be interpreted as 
males initially migrating earlier than the other males 
to pick among the receptive multiparous females, and 
as males subsequently migrating slower with a female 
in grasp. Such a scenario, however, is still hypothetical 
considering the long distances (>100 km) migrated and 
that the interpreted periods of grasping and carrying 
(>2 months) are longer than those reported in the lit- 
erature (Sainte-Marie et ah, 2008). 
