166 



Fishery Bulletin 90(1). 1992 



in sand-filled depressions on the mounds. Some were 

 almost entirely covered with sand and the shells were 

 devoid of algae. It is possible that conch in the sand 

 habitat were underestimated during winter months 

 because of burial behavior; however, tag return data 

 (Stoner and Sandt 1992) suggest that most adult conch 

 move to hardground or rubble for the winter months. 



The mean shell length of pairing, copulating, and 

 egg-laying females (i 226mm, SD 23.6, n 180) was 

 2.3% larger than that for males in reproductive be- 

 havior (x 221mm, SD 17.4, n 180). However, pairwise 

 ANOVA, using female-male pairs as statistical blocks, 

 indicated no significant differences in shell length 

 among pairs (F 1.155, p 0.358), or between females and 

 males (F 0.847, p 0.366). Results were similar in the 

 case of copulating conch (among pairs, F 1.105, p 0.430; 

 between females and males, F 0.112, p 0.743). 



Reproductive activity in Stromhus gigas was rare on 

 hardbottom substrata (i.e., mounds, rubble and boulder 

 areas). Ninety-four percent of the pairing conch were 

 observed on sand, none were observed on rubble, and 

 only 5.6% were found on hardbottom (Table 1). Eighty- 

 five percent of copulating conch were found on sand, 

 with small percentages found on rubble and hard- 

 bottom. 



A total of 149 egg-laying females were observed be- 

 tween April and October 1988; except for one female 

 found laying eggs on hardbottom in area Bl, all were 

 found spawning on sand (Table 1). Nine observations 



100 



UJ 90 

 < 



> se- 



ct: 

 < 



o 

 a: 



LU 

 CD 



70 

 60-1- 

 50 

 40 

 30 

 20 

 10 

 



N = 397 



h _ 



SHELL LENGTH (urn) 



Figure 5 



Length-frequency distribution for veligers collected near Lee 

 Stocking Island, Bahamas, May-September 1988 (n 397). 



of simultaneous pairing and egg-laying were made; only 

 one simultaneous copulation and egg-laying was ob- 

 served. All 148 females on sand were oriented perpen- 

 dicular to sand waves, with the anterior end of the shell 

 elevated near the crest of the wave and the egg mass 

 near the trough. Mean grain size of sediments collected 

 immediately adjacent to egg-laying females was 0.389 

 B (774/im) (SD 0.248, n 8), which is in the coarse-sand 

 classification. Sediments were poorly sorted as indi- 

 cated by a mean sorting coefficient of 0.967 Q (SD 

 0.302, n 8). Organic content was 3.45% of dry weight 

 (SD 0.69, n 8). 



Larval abundance 



Conch larvae were first collected at the Reproductive 

 Site on 2 June 1988 at a density of 0.26 larvae/10 m^ 

 (Table 2), 5 weeks after the first egg mass was dis- 

 covered (Fig. 3B). Surface- and bottom-water temper- 

 atures were 27.5°C and 25.8°C, respectively. Veliger 

 density at the Reproductive Site ranged from 0.04 

 larvae/10 m'^ on 6 June to 0.99 larvae/10 m^ on 16 

 June. No plankton collections were made at this site 

 between 29 June (0.30 larvae/10 m^) and 23 August 

 (0.77/10 m^); during this interval, emphasis was 

 shifted to the Children's Bay Cay site on Exuma Bank. 

 Larvae were not found until 6 June in Rat Cay cut 

 and 20 June in Adderley Cay cut (Fig. 3C). By the end 

 of June, surface-water temperature was near maximum 

 (29.5°C and 29°C) in the two inlets. Highest density 

 in the tidal passes was 4.46 larvae/10 m^ on 21 July at 

 the Rat Cay cut, concurrent with maximum egg-laying 

 frequency (13%) and surface and bottom temperatures 



