Somerton and Donaldson. Biology of Chionoecetes tanneri and C angulatus 



355 



the high incidence of barrenness was due simply to our 

 sampling between times of molting and egg extrusion. 



For mature male C. tanneri and C. angulatus, the 

 relative abundance of the four shell condition cat- 

 egories differed significantly between species 

 <X 2 =21.4, P<0.001), primarily because there were 

 considerably more C. angulatus males in a recently 

 molted condition (Table 3). The high incidence of re- 

 cently molted C. angulatus males was not due to the 

 chance capture of a large molting aggregation, be- 

 cause recently molted individuals were found at 

 many of the sampling sites. Therefore, it is likely 

 that the timing of the male molting season differs 

 between species. 



For both species, however, the relative abundance 

 of the four shell conditions differed between sexes 

 (C. tanneri,x 2 =104.1,P<0.001;C. angulatus, x 2 =130.0, 

 P<0.001) primarily because males had lower shell- 

 condition scores than did females. Such between-sex 

 differences in shell condition scores could reflect dif- 

 ferences in the timing of the molt relative to sam- 

 pling, differences in preferred habitat, or differences 

 in adult mortality rate. Alternatively, such differ- 

 ences in shell condition could indicate that mature 

 males have molted more recently, on average, than 

 adult females, raising the question of whether males 

 cease molting at maturity. Jamieson et al. (1990) 

 believed that male C. tanneri undergo a terminal 

 puberty molt and are therefore similar to C. opilio, 

 for which a male terminal molt has been clearly es- 

 tablished (Conan and Comeau, 1986). However, 

 Tester and Carey (1986) also found a between-sex 

 difference, similar to our study, in the index of 

 postmolt age for C. tanneri off Oregon; mature males 

 exhibited considerably lower incidence of exoskeleton 

 damage from chitonoclastic bacteria than did mature 



females. This sexual difference in exoskeleton dam- 

 age was interpreted as an indication that male C. 

 tanneri continue to molt after maturity. Although our 

 shell-condition data were consistent with the obser- 

 vations of Tester and Carey (1986), we are not con- 

 vinced that this indicates that males contintue to 

 molt. 



Weight-carapace-width relationship 



The increase in male body weight with carapace 

 width ( Fig. 8 ) was not significantly different between 

 the two species (ANCOVA, P=0.92; Table 4), there- 

 fore a single function was fitted to the combined data. 

 This similarity in the weight-width relationship re- 

 flects a remarkable similarity in the shape of 

 C. tanneri and C. angulatus compared with shallow- 

 water species of Chionoecetes. For example, the pre- 

 dicted weight at 120 mm CW is 505 gm for both 

 C. tanneri and C. angulatus males. The weight of a 

 similar-size C.japonicus, another slope-dwelling spe- 

 cies, is 588 gm ( Watanabe and Suzuuchi, 1983), fairly 

 close to C. tanneri and C. angulatus. However, the 



