Nichol and Somerton: Seasonal migration of mature males of Chionoecetes opilio in the eastern Bering Sea 
315 
mercial-size MM male snow crab, we examined the sea- 
sonal inshore and offshore migrations of these males to 
determine if their migrations contribute to the report- 
ed differences between distribution of MM male snow 
crab during summer and their distribution during win- 
ter. Second, by examining the summer distribution of 
mature females, we attempted to infer the components 
of the female stock that are associated with and mate 
with large MM males. Finally, we compared the distri- 
bution of both large and small MM males with that of 
mature females to assess the potential for size-specific 
male-female mating associations. 
Materials and methods 
Tagging 
A total of 277 morphometrically mature male snow 
crab (96-134 mm CW) were tagged and released with 
pressure-and-temperature-recording DSTs on 18-22 
April 2010 (n=120) and 7-8 March 2011 (n=157), near 
the end of each fishing season to ensure that tagged 
crab were not recaptured until the following year. Tag- 
ging operations occurred on the winter snow crab fish- 
ing grounds northwest of the Pribilof Islands at ap- 
proximately 57°35 N in 2010 and about 100 km farther 
north at 58°30 N in 2011 (Fig. 1). DSTs were attached 
to spaghetti tags that were wrapped around the cara- 
pace of the crab between the first and second walking 
legs. Because male snow crab do not molt after they 
reach maturity, the effect of tagging on their behavior 
and mortality was assumed to be negligible. In April 
2010, an additional 221 snow crab were tagged and 
released with numbered spaghetti tags without an at- 
tached DST as a control to determine whether the ad- 
ditional DST attachment affected capture rate, as well 
as to help examine site fidelity. 
Crabs were captured and tagged aboard commercial 
crab pot fishing vessels Kiska Sea (in 2010) and Pacific 
Sun (in 2011) during normal commercial fishing opera- 
tions, and they were released within 10 min of capture 
at the same location. All tagged male crabs had large 
claws and had new to slightly worn hard shells, condi- 
tions that predominated in the catches during the time 
of tagging. Only crabs that possessed all their limbs 
were selected for tagging. Tagged crabs were recap- 
tured by commercial crab pot vessels during the fol- 
lowing winter and spring snow crab fisheries in 2011 
and 2012, and a tag reward program was implemented 
to provide an incentive to return tags. Locations where 
crabs were recaptured were documented by the fisher- 
men who returned tags. 
The DSTs, Cefas G5 Long Life 5 tags with 2 MB of 
memory (Cefas Technology Limited, Lowestoft, UK), 
measured depth (pressure) at 1-min intervals, with an 
5 Mention of trade names or commercial companies is for iden- 
tification purposes only and does not imply endorsement by 
the National Marine Fisheries Service, NOAA. 
accuracy of ±2 m and precision of <0.08 m, and temper- 
ature at 30-min intervals, with an accuracy of ±0.1°C 
and precision of 0.03°C. DSTs were bullet-shaped with 
dimensions of 8x31 mm and weighed 1 g in water. 
Analyses of snow crab depth and ambient temperature 
The shelf of the eastern Bering Sea slopes down gradu- 
ally from northeast to southwest from the Alaska main- 
land ( i.e. , north of 58°N) out to the shelf break (bottom 
depth: approximately 200 m); therefore, changes in tag 
depth were used as proxies or indicators of inshore and 
offshore movements (Fig. 1). Because migrations likely 
included movements parallel to bottom depth contours 
(i.e., movements in northwest and southeast directions), 
exact migration pathways could not be determined. 
For each recaptured crab, the recorded tag depths 
were plotted against time (e.g., month) to determine 
whether seasonal inshore and offshore migrations were 
made and whether migrations were consistent among 
all individuals. Temperatures also were plotted against 
time to document the temperatures of areas inhabited 
by snow crabs in the eastern Bering Sea. In a few cas- 
es, tag temperatures were compared with temperatures 
collected during the NMFS summer bottom trawl sur- 
vey, to corroborate the position of a crab from release 
and recapture positions and to indicate their proximity 
to the cold pool. 
Distribution of mature females 
The distributions of primiparous and multiparous fe- 
males were plotted with data from the 2010 and 2011 
NMFS summer bottom trawl surveys (Foy and Ar- 
mistead, 2013; Lauth and Nichol, 2013) to examine 
the extent to which their distributions overlapped with 
tagged MM males and to infer whether the migration 
of large MM males would be necessary to create mat- 
ing opportunities. A critical assumption for this com- 
parison was that the mature (i.e., primiparous and 
multiparous) female distributions observed during the 
summer survey were representative of the mature fe- 
male distributions during the preceding winter-spring 
mating period. Primiparous females were identified as 
those females with uneyed eggs, clutch sizes 1/8 to 3/4 
full, and soft to clean hard shell conditions. Multipa- 
rous females were identified as those females with ei- 
ther uneyed or eyed eggs, full clutch sizes, and hard 
shells with scratches or wear. 
Distribution of morphometrically mature males 
Broad-scale geographic distributions of MM male snow 
crabs during summertime were analyzed with data col- 
lected annually (1989-2011) during the NMFS summer 
bottom trawl survey (Foy and Armistead, 2013; Lauth 
and Nichol, 2013), where stations were fixed and posi- 
tioned 37 km apart from each other. Distributions were 
plotted for 4 male categories; that is, for 2 different 
size classes (70-100 mm CW and >100 mm CW), each 
