FISHERY BULLETIN: VOL. 84, NO. 4 



with abdomen widths > 50 mm (corresponding to 

 carapace widths >85 mm) form a well-defined group 

 (Fig. 3) of adults. The mean carapace width for adult 

 male and female crabs in this study was 142.7 and 

 102.3 mm respectively and was compared with the 

 mean carapace widths of 148.9 and 102.5 mm for 

 females given by Pereyra (1972) for adult C. tan- 

 neri collected south of the Columbia River mouth. 

 Brown and Powell (1972) reported a similar corre- 

 spondence in adult carapace widths for C. bairdi 

 collected from locations in Alaska. The large varia- 

 tion in size of mature male C. bairdi in the eastern 

 Bering Sea was clearly related at the clinal varia- 

 tion temperature (Somerton 1981). 



Seven modes representing juvenile instars are evi- 

 dent from the size-frequency histograms (Fig. 4). 

 The mean carapace widths for each juvenile instar 

 were calculated and subsequently the increase in 

 CW per molt was computed (Table 1). The average 

 increase at each molt for instars I-VII is 39% and 

 there is no difference in growth increment of juve- 

 nile males and females In a laboratory study using 

 C. opilio, Miller and Watson (1976) reported that 

 growth per molt for immature females was signifi- 

 cantly greater than for immature males. But the 

 findings of Hilsinger et al. (1975) agree with ours. 

 They found no difference in growth rate for juvenile 



male and female C. bairdi and reported a constant 

 growth rate of 27% for juvenile females. The change 

 in the slope of the regression lines of the log-log plots 

 of the allometric measurements of C. tanneri (Fig. 

 5) indicated a change in the rate of growth only at 

 sexual maturity. Chionoecetes tanneri, like C. opilio 

 (Watson 1970), showed two growth phases, one for 

 juveniles and one for adults. 



If C. tanneri eggs hatch predominantly in winter 

 (January-March) and the total larval life is 80 d, the 

 recruitment of the smallest crab stage (CW = 4) to 

 the population in June- July is in agreement with our 

 findings. Instars can be followed from 4 mm CW 

 (instar I) in June and July 1974, to 5.5 cm CW (in- 

 star II) in August 1974, to 7.5 mm CW (instar III) 

 in January 1975 (Fig. 6). The smallest specimens 

 sampled by the trawls were about 10 mm CW, and 

 there were relatively large numbers of these instar 



IV specimens in April 1973 which molted to instar 



V by August and to instar VI in October 1973 (Fig. 

 7). No growth of these instar VI crabs is evident 

 from the November 1973 or March 1974 data. We 

 estimate approximately 20 mo from egg hatching 

 to instar VII (CW = 26.8 mm) (Fig. 8). 



Observations on general carapace condition and 

 abundance of epifauna indicate that adult male C. 

 tanneri do molt frequently enough to maintain their 



E 

 E 



T3 



CD 



E 

 o 



< 



70i 



60 



50 



2 40 



30 



20 



10 



N=851 



   



.♦♦% 





 



♦**♦ 



«♦♦ 



10 20 30 40 50 60 70 80 90 100 110 120 130 



Carapace Width (mm) 



Figure 3.— Relationship between carapace width and abdomen width for juvenile and adult female Chionoecetes tanneri. 



976 



