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Fishery Bulletin 93(4). 1995 



means ranged from a low of 0.1°C in March 1992 to a 

 high of 3.0°C in August 1992 (daily records: low of- 

 0.3°C and high of 6.5°C). Photoperiod was controlled 

 to correspond to natural light rhythms. Individual 

 crabs were identified by a plastic tag tied around the 

 basipodite of one of the fourth or fifth pereiopods. 

 Crabs were fed frozen shrimp (Pandalus borealis) 

 semi weekly. Beginning in January 1992, tanks were 

 checked twice daily for molting individuals. 



Less than 12 hours after molting to maturity, each 

 female was placed in a 120-L tank that was either 

 empty or contained one male. Male mates were hard- 

 shelled adult crabs in either of three size categories, 

 40-60, 80-100, and 120-140 mm CW, or hard-shelled 

 adolescent crabs of 80-100 mm CW. Actual size 

 ranges were 48.6-59.8, 82-99.4, and 120.3-138.3 mm 

 CW for adult males, and 80.1-99.8 mm CW for ado- 

 lescent males. The female was left in the tank until 

 either eggs were extruded or 24 hours had elapsed. 

 The female was then allowed to harden her shell for 

 5-6 days in isolation and was monitored daily to de- 

 tect delayed egg extrusion. Finally, the female was 

 retagged and transferred to a communal holding tank 

 for females. Males were used once only and then held 

 in communal tanks for up to 14 months after mat- 

 ing, to determine whether they would moult. 



Egg color of each primiparous female was moni- 

 tored at least every 2-3 months in order to evaluate 

 development of the clutch. About one month before 

 the anticipated period of hatching, i.e. May to June 

 1993, females bearing ripe eggs were isolated in ei- 

 ther 90- or 120-L tanks with flowing seawater. One 

 hard-shelled adult male of 78.8-119.5 mm CW was 

 introduced into the tanks of randomly selected fe- 

 males in each of two groups, representing those fe- 

 males that had initially mated either with adoles- 

 cent (3 females remated) or with adult (17 females 

 remated) males. The tanks were monitored once a 

 day to detect the onset of hatching and, where ap- 

 propriate, mating behavior. 



Ten to 12 weeks after the second clutch was ex- 

 truded, a sample of at least 25 eggs was taken at the 

 base of each of the eight pleopods of 58 females. Pleo- 

 pods on the right-hand side were assigned numbers 

 1 to 4, and those on the left-hand side were assigned 

 numbers 5 to 8, from front to rear. During sampling, 

 females did not shed or lose more than =50 eggs in 

 excess of those removed by the observer. Samples of 

 eggs from each pleopod were fixed and stained to 

 reveal nuclear DNA by means of a technique adapted 

 from Dube et al. (1985) and Dufresne et al. (1988). 

 Eggs were fixed for one hour in a solution of 97% 

 glucamine-acetate (GA) buffer, 2% formaldehyde, and 

 1% Triton, and then rinsed in GA buffer. The GA buffer 

 was composed of 250 mM N-methyl glucamine, 250 mM 



potassium gluconate, 50 mM Hepes, and 10 mM EGTA, 

 adjusted to pH 7.4 with glacial acetic acid. Eggs were 

 then stained for one hour in a solution of 0.5 ug Hoescht 

 dye per mL of GA buffer and were then rinsed twice 

 and preserved in GA buffer at 4°C. The numbers of 

 divided and undivided eggs in each pleopod sample were 

 determined by epifluorescent microscopy. 



Females were examined to evaluate clutch size one 

 week after eggs were sampled from second clutches. 

 Female abdomens were indexed for repleteness with 

 eggs on a scale of (empty) to 4 (very full). The index 

 of clutch size is similar to the more refined percent 

 clutch statistic, where actual clutch size is rated as 

 a percentage of the largest clutch a female decapod 

 of a given size can hold (Blau, 1986). The egg replete- 

 ness index and the percent clutch statistic both cor- 

 relate significantly with the actual number of eggs 

 held by a female decapod (Shields et al., 1990; Sainte- 

 Marie, unpubl. data). 



Results and discussion 



Females molted to maturity from 8 January to 12 

 April 1992 and ranged in size from 49.7 to 74.4 mm 

 postmolt CW. Only females that survived until Au- 

 gust 1993 were analyzed in this study. Overall mor- 

 tality of females from time of maturity molt until 

 August 1993 was 50.3% (of 155) but was unrelated 

 to mating status (mated or unmated) or to the mate's 

 identity (maturity, CW). Of the 11 adolescent males 

 that were mated, eight molted 3-57 days ( x =30 d) 

 after mating, one molted 384 days after mating, and 

 two died within 14 months of mating. No adult male 

 molted over the 14-month period, consistent with the 

 hypothesis that adult males are in anecdysis 

 (O'Halloran, 1985; Conan and Comeau, 1986). 



Of the nine females that were initially unmated, 

 only four extruded a first clutch (Table 1 ) four or more 

 days after their molt to maturity. All of the 68 fe- 

 males that initially mated extruded a first clutch: 

 56 did so while in the presence of their mate and 12 

 extruded later, i.e. 1-5 days after separation from 

 their mate. First clutches did not develop and hatch 

 on the four females that were unmated and on the 

 12 females that were mated but slow to spawn. 

 Sainte-Marie and Lovrich (1994) reported that de- 

 layed spawning occurred in C. opilio when few or no 

 sperm were delivered to females at mating. These 

 authors hypothesized that females can gauge the 

 contents of their spermathecae and, when insuffi- 

 ciently inseminated, postpone extrusion in expecta- 

 tion of a more fecund mate. By comparison, only two 

 females that extruded eggs while in the presence of 

 their mate failed to hatch their first clutch. Clutches 



