Somerton and Donaldson Biology of Chionoecetes tanneri and C angulatus 



351 



Depth distribution 



Both species occurred in the deeper por- 

 tion of the survey area; few individuals of 

 either species were encountered shallower 

 than 300 m (Fig. 4). For C. tanneri, the 

 mean depth of mature males (752 m) was 

 not significantly different from the mean 

 depth of mature females (709 m; /-test, 

 P=0.38). This is in contrast to the summer- 

 time depth distributions of C. tanneri re- 

 ported off British Columbia (males 580- 

 670 m, females 670-720 m, Jamieson et 

 al., 1990) and off Oregon (males 640-686 

 m, females 503-549 m, Pereyra, 1966) 

 where mature males were found at dis- 

 tinctly shallower depths than those for 

 mature females. Thus in the eastern 

 Bering Sea, C. tanneri does not show a 

 clear depth segregation of males and fe- 

 males as is seen in more southerly lati- 

 tudes, and the depths occupied by both 

 sexes are greater. 



For C. angulatus, the mean depth for 

 mature males (647 m) was significantly 

 less than the mean depth for mature fe- 

 males (748 m; /-test, P<0.001>, indicating 

 that this species does appear to have the 

 same pattern of sexual segregation by 

 depth as that displayed by C. tanneri in 

 more southerly latitudes (Pereyra, 1966). 

 The depth distribution reported for C. 

 japonicus (Yosho and Hayashi, 1994) in- 

 dicates that the greatest abundance of 

 both sexes occurs at about 1,000 m. Al- 

 though this finding suggests that C. 

 japonicus may occur deeper than C. 

 angulatus, it is clear (Fig. 4) that the dis- 

 tribution of C. angulatus extends into deeper water 

 than was covered in our survey and that our esti- 

 mates of mean depth are low (C. angulatus has been 

 reported as deep as 2,974 m [Hart, 19821; in fact, the 

 type specimen of C. angulatus was taken quite near 

 our sampling site in 2,549 m [Rathbun, 1932]). 



Juvenile male C. tanneri were found in signifi- 

 cantly shallower waters than were mature males la- 

 test, P<0.001), whereas juvenile male C. angulatus 

 were not significantly different (P=0.30) in mean 

 depth from mature males. This is in contrast to the 

 depth distribution reported for C. tanneri from Brit- 

 ish Columbia to Oregon where there is a strong depth 

 segregation by size, where juveniles are found in 

 deeper water than are adults (Pereyra, 1968; Jamie- 

 son et al., 1990). The observed between-area differ- 

 ence in vertical distribution indicates that the fac- 



Carapace width 



Figure 3 



Carapace width distribution for male and female Chionoecetes tanneri 

 and C. angulatus. The total number of individuals measured (rc ) in each 

 category is indicated for each sex and species. 



tors producing the size variation with depth at more 

 southerly latitudes do not function similarly in the 

 Bering Sea. Pereyra (1968) hypothesized that C. 

 tanneri larvae are advected offshore by Ekman trans- 

 port and settle to the bottom in deep water. The 

 strong variation in size with depth then results from 

 a shoreward ontogenetic migration of the young 

 crabs. In the region where we surveyed, however, 

 advection of the near-surface water is either quite 

 weak or onshore, 2 rather than strongly offshore. Thus 

 the difference in the observed size variation with 

 depth between the Bering Sea and Oregon may be due 

 to differences in the local oceanographic conditions. 



2 Pease, C. 1995. Pacific Marine Environmental Laboratory, 

 Seattle, Washington. Personal commun. 



