BIOLOGICAL ASPECTS OF 



THE SPRING BREEDING MIGRATION OF 



SNOW CRABS, CHIONOECETES OPILIO, IN 



BONNE BAY, NEWFOUNDLAND (CANADA) 



The occurrence of an annual (April-May) deep- to 

 shallow-water breeding migration of snow crabs, 

 Chionoecetes opilio, in Bonne Bay, on the west coast 

 of Newfoundland, has been documented by Hooper 

 (in press). In addition to being the first record of this 

 phenomenon in this species, his observations con- 

 tradict some generally accepted conclusions regard- 

 ing the species' reproductive biology. The most 

 significant of these are that females undergo a ter- 

 minal molt to maturity and do not mate in the hard 

 shell condition (Ito 1967; Watson 1972; Tkkeshita and 

 Matsuura 1980). 



Little morphometric sampling data are included 

 in Hooper's general description of the breeding 

 migration. The purpose of this paper is to provide 

 a more detailed description of various biological 

 aspects of the phenomenon, such as size difference 

 between paired males and females, and condition of 

 the external egg masses, ovaries, and spermathecae 

 during the breeding period. 



Materials and Methods 



Three hundred and three sexually paired snow 

 crabs were collected during three field trips to Bonne 

 Bay from 24 April to 29 May 1984 by scuba diving 

 (10-30 m depth). Each pair was kept in a separate 

 mesh bag. At the surface, each crab was measured 

 to the nearest millimeter (maximum carapace width 

 (CW)) and its shell condition (soft, new/hard, or 

 old/hard) determined. The eggs of females were ex- 

 amined to determine their stage of development. 

 Following this, males were tagged with Floy vinyl 

 "T-bar" tags (Tkylor 1982) and released, and females 

 were either tagged and released, or retained for later 

 examination of their ovaries and spermathecae in the 

 laboratory. 



Results 



Size Distribution 



Size distributions were unimodal for each sex but 

 with no overlap in their carapace widths (Fig. 1). 

 Males ranged from 89 to 140 mm (x = 116.4 mm) 

 CW and females from 55 to 86 mm (x = 67.8 mm). 

 Other than the fact that males were invariably larger 

 than females, there was no discernible relationship 

 between size of the male and size of the female with 



which it was paired (Fig. 2). Mean sizes of females 

 paired with small, medium, and large size males were 

 the same (P < 0.005, Bartlett's test of homogeneity 

 of variance). 



The mean difference in carapace width between 

 paired males and females increased from 21 mm at 

 89 mm male CW to 70 mm at 140 mm. Only 3 males 

 in 303 pairs were smaller than 95 mm, the legal size 

 limit. 



Female Reproductive Condition 



During the 24-27 April sampling period, 92% of 

 the females carried full clutches of eyed eggs and 

 the remainder had liberated all or most of the lar- 

 vae (Table 1). By 7-11 May, 59% had empty brood 

 pouches indicating that hatching was well advanced. 

 However, during 22-25 May, 53% of the females 

 were carrying full clutches of eyed eggs and only 

 39% had empty brood pouches. This increase in 

 relative abundance of females with eyed eggs could 

 have resulted from a return to deeper water of 

 females that had liberated larvae or an influx of new 

 animals from deeper water. Dead eggs were carried 

 by 1.4% of females examined. All females dissected 

 (77) had ripe (extrusion imminent) ovaries (Table 2); 

 however, only two with partially extruded clutches 



Table 1. — Summary of observations on external 

 egg masses of female Chionoecetes opilio col- 

 lected in Bonne Bay, Newfoundland, April-May 

 1984. 



FISHERY BULLETIN: VOL. 83, NO. 4, 1985. 



707 



