313 
NOAA 
National Marine 
Fisheries Service 
Abstract— Seasonal migration of 
commercial-size (>102 mm carapace 
width [CW]), morphometrically ma- 
ture (MM) snow crabs (Chionoecetes 
opilio ) from the eastern Bering Sea 
was examined in relation to the sum- 
mer distribution of mature females 
to identify spatiotemporal overlap 
of males and females and determine 
the likelihood of mating associations 
for specific reproductive stages. 
Depth variation associated with this 
migration was examined to deter- 
mine whether seasonal migrations 
contribute to previously recognized 
spatial differences in distributions 
of commercial-size males caught in 
the winter fishery and in the Na- 
tional Marine Fisheries Service sum- 
mer bottom trawl survey. Depth data 
from 33 data storage tags attached 
to commercial-size MM males dur- 
ing 2010 and 2011 indicated that 
most males moved inshore during 
spring — a movement that would al- 
low them to mate with multiparous 
females but not with pubescent-pri- 
miparous females. Smaller tagged 
males (100-102 mm CW) underwent 
more extensive inshore migrations, 
and several of them traveled more 
than 100 km in one direction. Both 
tagging and distribution data indi- 
cated that most commercial-size MM 
males remained predominantly on 
the outer shelf throughout the year 
(despite some inshore movements 
during spring) and, therefore, these 
males did not contribute greatly to 
the spatial differences observed be- 
tween winter and summer. 
Manuscript submitted 13 November 2014. 
Manuscript accepted 15 May 2015. 
Fish. Bull. 113:313-326 (2015). 
Online publication date: 4 June 2015. 
doi: 10. 7755/FB. 113.3.7 
The views and opinions expressed or 
implied in this article are those of the 
author (or authors) and do not necessarily 
reflect the position of the National 
Marine Fisheries Service, NOAA. 
Fishery Bulletin 
nr established 1881 
Spencer F. Baird 
First U S. Commissioner 
of Fisheries and founder 
of Fishery Bulletin 
Seasonal migrations of morphometrically 
mature male snow crab ( Chionoecetes opilio ) 
in the eastern Bering Sea in relation to 
mating dynamics 
Daniel G. Nichol (contact author) 
David A. Somerton 
Email address for contact author: dan.nichol@noaa.gov 
Resource Assessment and Conservation Engineering Division 
Alaska Fisheries Science Center 
National Marine Fisheries Service, NOAA 
7600 Sand Point Way NE 
Seattle, Washington 98115 
Migrations of snow crabs (Chionoece- 
tes opilio ) differ between sexes and 
among different size classes, result- 
ing in distributions that are highly 
structured and complex (Ernst et 
al., 2005). In the eastern Bering Sea, 
these migrations depend partially on 
bottom temperature gradients (Ernst 
et al., 2005) and can vary annually 
depending on the extent of the “cold 
pool” (Kotwicki and Lauth, 2013), 
a near bottom layer of cold (<2°C) 
water that forms across mid-depths 
(50-100 m) of the eastern Bering Sea 
shelf. On the basis of data from the 
eastern Bering Sea shelf collected 
during the National Marine Fisher- 
ies Service (NMFS) annual summer 
bottom-trawl survey, immature crabs 
of both sexes undertake down-slope 
ontogenetic migrations that are 
generally from the northeast to the 
southwest (Otto, 1998; Zheng et al., 
2001; Ernst et al., 2005). Upon reach- 
ing full maturity, both sexes undergo 
a terminal molt in the spring, after 
which they are thought to continue 
to migrate into deeper water (Ore- 
sanz et al., 2004; Ernst et al., 2005; 
Parada et al., 2010). For commer- 
cial-size males, >102 mm in cara- 
pace width (CW), this migration is 
assumed to culminate on the outer 
shelf (depths of 100-200 m), where 
the winter commercial fishery is con- 
centrated (Orensanz et al., 2004). 
Less is known about smaller termi- 
nally molted males, but they are as- 
sumed to reside inshore of the com- 
mercial-size males. 
Male migrations likely differ be- 
fore and after the terminal molt. 
Because the transformation from a 
small-clawed “adolescent” stage to a 
large-clawed morphometrically ma- 
ture (MM) stage coincides with the 
terminal molt for males, these stages 
have been distinguished by using the 
relationship of carapace width (CW) 
to chela height (CH) (Comeau and 
Conan, 1992; Stevens et al., 1993; 
Rugolo et al. 1 ; Tamone et al., 2007). 
Because members of a cohort can 
reach maturity over multiple ages, 
the size distribution of MM males 
overlaps that of adolescent males. 
Although adolescent males are some- 
times capable of mating, MM males 
1 Rugolo, L., D. Pengilly, R. Macintosh, 
and K. Gravel. 2005. Reproductive po- 
tential and life history of snow crabs in 
the eastern Bering Sea. In Bering Sea 
snow crab fishery restoration research: 
final comprehensive performance report. 
(D. Pengilly and S. E. Wright, eds.), p. 
57-323. NOAA Cooperative Agreement 
NA17FW1274. Div. Commer. Fish., 
Alaska Dep. Fish Game, Juneau, AK. 
