Fertilization of the second clutch of 

 eggs of snow crab, Chionoecetes 

 opilio, from females mated once or 

 twice after their molt to maturity 



Bernard Sainte-Marie 



Direction des Sciences des Peches, Institut Maurice-Lamontagne 

 Mmistere des Peches et des Oceans, 850 Route de la Men C.P. 1 000 

 Mont-Joli. Quebec, Canada G5H 3Z4 



Chantal Carriere 



Departement d'Oceanographie. Universite du Quebec a Rimouski, 

 Rimouski, Quebec, CANADA G5L 3A1 



Females of the commercially impor- 

 tant genus Chionoecetes (Brachyura: 

 Majidae) copulate and extrude eggs 

 for the first time soon after a ter- 

 minal molt to maturity (Watson, 

 1972; Adams, 1982). Females pre- 

 paring for the molt to maturity are 

 termed "pubescent," those bearing 

 a first clutch are "primiparous," and 

 those bearing a second or subse- 

 quent clutch are "multiparous." 

 Spermathecae allow females to 

 store sperm that is not expended at 

 spawning (Watson, 1970; Adams and 

 Paul, 1983; Beninger et al., 1988). 



The importance of sperm stored 

 from the first mating to reproduc- 

 tive output is partially documented 

 for the Tanner crab, Chionoecetes 

 bairdi (Adams and Paul, 1983; Paul 

 and Paul, 1992), but remains 

 largely unknown for the snow crab, 

 Chionoecetes opilio (Elner and 

 Beninger, 1992). Watson (1970) ob- 

 served that some female C. opilio 

 hatched a clutch and then extruded 

 a new clutch of fertilized eggs with- 

 out remating. Assuming that copu- 

 lation occurs only at the molt to 

 maturity, he concluded that female 

 C. opilio can produce more than one 

 batch of fertile eggs from a single 

 mating (also see Watson, 1972). 

 Subsequently, field and laboratory 

 studies have shown that multipa- 

 rous females of C. opilio and of C. 



bairdi can, and often do, mate be- 

 fore extruding a new clutch 

 (Adams, 1982; Paul, 1984; Taylor 

 et al., 1985; Conan and Comeau, 

 1986; Hooper, 1986; Claxton et al., 

 1994; Moriyasu and Conan 1 ). Be- 

 cause the female C. opilio that Wat- 

 son observed spawning were of un- 

 known reproductive history (i.e. 

 number of matings and clutches), 

 the conclusion that one mating is 

 sufficient to produce more than one 

 viable clutch is suspect and war- 

 rants further investigation. 



In C. bairdi, the viability of 

 stored sperm apparently decreases 

 over time, and some multiparous 

 females may fail to spawn or may 

 extrude unfertilized eggs when iso- 

 lated from males for more than one 

 breeding season (Paul, 1984). Fur- 

 thermore, in laboratory experi- 

 ments with C. bairdi, Paul and 

 Paul ( 1992) found that 10 out of 11 

 females did not receive enough 

 sperm at the first mating to fertil- 

 ize more than one clutch. These in- 

 vestigators suggested that this may 

 also be the case for C. opilio. How- 

 ever, Sainte-Marie and Lovrich 

 ( 1994) estimated that primiparous 

 C. opilio usually have enough 

 stored sperm to fertilize at least one 

 additional clutch. Therefore, we 

 compared the size of the second 

 clutch and the proportion of divided 



(i.e. fertilized) eggs for female C. 

 opilio mated only at the molt to 

 maturity with those values ob- 

 tained for females with access to 

 males at a second spawning. 



Materials and methods 



Males and pubescent females were 

 collected in Baie Sainte-Marguer- 

 ite (ca. 50°06'N, 66°35'W), north- 

 west Gulf of Saint Lawrence, from 

 September through October 1991, 

 and in March 1992. Carapace width 

 (CW) of females and males, and 

 right chela height (CH) of males, 

 were measured to the nearest 0.1 

 mm as described in Sainte-Marie 

 and Hazel (1992). Males >40 mm 

 CW were classified on the basis of 

 chela allometry into either of two 

 sperm-producing forms (Comeau 

 and Conan, 1992), designated ado- 

 lescent or adult following terminol- 

 ogy in Sainte-Marie et al. (in press). 

 (Other investigators have used the 

 terms "small-clawed," "morpho- 

 metrically immature," or "juvenile" 

 to designate adolescent males, and 

 "large-clawed" or "morphometri- 

 cally mature" to designate adult 

 males.) Classification was initially 

 done by visual comparison of indi- 

 vidual male measurements with 

 scatterplots of CH on CW for a large 

 sample of males from the source 

 site, and verified a posteriori by 

 using a site-appropriate discrimi- 

 nant function from Sainte-Marie 

 and Hazel (1992). 



Crabs were segregated by sex in 

 tanks of either 1,400 or 2,000 L 

 with flowing seawater. The mean 

 temperature of seawater over the 

 year following the first mating of 

 females was 1.5°C, and monthly 



1 Moriyasu, M., and G. Y. Conan. 1988. 

 Aquarium observation on mating behav- 

 ior of snow crab, Chionoecetes opilio. Int. 

 Counc. Explor. Sea CM. (Council meet- 

 ing) 1988/k:9, 14 p. 



Manuscript accepted 27 March 1995. 

 Fishery Bulletin 93:759-764 (1995). 



759 



