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Fishery Bulletin 90(4), 1992 



shows, this difference is sometimes negUgible. How- 

 ever, BKC were readily distinguished from RKC by 

 their proportionately shorter rostrums, larger eyes, 

 and larger bodies, but the differences were not as great 

 as those seen in the Pribilof Islands. Zoeae in both loca- 

 tions appeared to gain additional telson spines with lar- 

 val stage, a pattern noted previously for other lithodid 

 larvae by Kurata (1964). While rostrum length alone 

 was not reliable for separating the two species (due to 

 intraspecific variation between the two areas), the pro- 

 portion of rostrum length to carapace length remained 

 constant and appears to be a useful method of differen- 

 tiating the two. Whether this is reliable in other areas 

 is not known, but it is consistent with illustrations in 

 published descriptions of the two species (Fig. 9). 



Of particular interest is the intraspecific variability 

 exhibited both between the two areas and within the 



population in Herendeen Bay. While there were no 

 significant differences between populations of RKC, all 

 linear measurements of BKC zoeae from Herendeen 

 Bay averaged 10-12% smaller than those of conspe- 

 cifics from the Pribilof Islands. The cause of this varia- 

 tion is not known, but environmental factors such as 

 temperature can affect both the number of decapod 

 larval stages (Knowlton 1974) and their morphology 

 (Shirley et al. 1987). Temperatures differed con- 

 siderably between the two areas at the time of larval 

 collection. At the Pribilof Islands in May 1983 the water 

 was 2-4°C, and -1-1.5°C in April 1984 (Armstrong 

 et al. 1985). In Herendeen Bay larvae stayed above a 

 40m thermocHne in water 2.5-8.5°C, and develop- 

 mental times were exceptionally fast (Wainwright et 

 al. 1991). 



BKC have an extremely disjunct distribution (Somer- 

 ton 1985), and it is also possible that size differences 

 could be related to their reproductive isolation. But 

 although local environmental features or isolation may 

 explain differences between the two populations, they 

 are unlikely to account for the variation seen within 

 the relatively small scale of Herendeen Bay. The eyes 

 of BKC zoeae having a 7 -i- 7 spine pattern were inter- 

 mediate in length between the 8 -i- 8 or 8 -i- 7 BKC larvae 

 and RKC from Herendeen Bay (Fig. 7). The cause of 

 such differences cannot be known without appropriate 

 experiments and genetic studies, but the recent report 

 of an adult RKC-BKC hybrid from the Sea of Okhotsk 

 (Nizyayev 1991) raises the possibility that some inter- 

 breeding may occur within the confines of Herendeen 

 Bay. 



Because all larvae were collected from the plankton 

 rather than hatched in captivity, we cannot state un- 

 equivocally that these differences in spine count are 

 due to intraspecific variation of BKC rather than a mix- 

 ture of other lithodid species. However, megalopae, 

 juveniles, and adults of RKC and BKC were collected 

 within Herendeen Bay during the course of this study; 

 despite extensive trawling, pot fishing, dredging, and 

 intertidal surveys, the only other lithodid found was 

 Hapalogaster grehnitzkii. Larvae matching the descrip- 

 tion for H. grebnitzkii were also the only other lithodid 

 zoeae occurring in the plankton samples. The large size, 

 shape, and position of the posterolateral carapace 

 spines, coupled with a lack of carapace sculpturing, 

 readily distinguish RKC and BKC zoeae from other 

 described species of Bering Sea lithodids. We believe 

 it is extremely unlikely that the variation is due to a 

 fourth, undescribed species. 



No single character for reliably separating BKC and 

 RKC zoeae was observed, but since the number of 

 telson spines is useful for differentiating the two 

 species in some areas (e.g., Pribilof Islands), we sug- 

 gest using this count along with the rostrum/carapace 



