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Fishery Bulletin 90(1). 1992 



Geographic comparisons of seasonality in reproduc- 

 tion must be interpreted cautiously due to different 

 methods, frequency and number of observations, an- 

 nual variation, and different habitat types. For exam- 

 ple, Brownell (1977) found that egg-laying in Los 

 Roques, Venezuela, extended later into the season in 

 deep water than in shallow water. Quantitative mea- 

 sures of reproductive activity provide a basis for ex- 

 amining mechanisms of seasonality, which is more 

 useful than records of reproductive occurrence. In all 

 studies that present seasonal curves for reproductive 

 behavior or numbers of egg masses (e.g., Davis et al. 

 1984, Weil and Laughlin 1984, Corral and Ogawa 1987, 

 and this study), maximum reproductive activity was 

 reported during the warmest months of the year. 



Control of gametogenesis and the physiology of egg 

 production are still unknown for 5. gigas, but histo- 

 logical studies of queen conch from Belize showed that 

 mature eggs and sperm were in the gonads year-round 

 (Egan 1985). External factors, therefore, are likely to 

 mediate seasonality in the intensity of reproductive 

 behavior and egg-laying. 



Emphasis in the past has been placed on the poten- 

 tial role of water temperature in reproductive activ- 

 ity. Similar to observations in Los Roques, Venezuela 

 (Brownell 1977, Weil and Laughlin 1984), reproductive 

 activity at Lee Stocking Island began with rise in 

 temperature. At both locations, reproductive activity 

 intensified with increasing temperature to reach its 

 maximum during the warmest period. Brownell (1977) 

 suggested that a sharp temperature decline of 1.1°C 

 from November to December was responsible for the 

 termination of queen conch egg-laying in Los Roques. 

 Similarly, egg-laying at Lee Stocking Island ended as 

 bottom-water temperature began to decline steadily 

 from 28.6°C in late September to 25.1°C in December. 

 On the other hand, pairing, copulation, and egg-laying 

 all decreased suddenly between August and Septem- 

 ber, during a period of high and relatively-stable water 

 temperature, near 28.5°C. 



Unlike the partial (early summer) correlation be- 

 tween reproductive behavior and temperature, pairing, 

 copulation, and egg laying were all positively correlated 

 with length of day throughout the year. Photoperiod, 

 therefore, may be one of the important environmental 

 variables which mediates the timing and length of 

 reproductive season. Synergistic interaction between 

 photoperiod and water temperature is possible. 



In addition to decreasing length of day in late sum- 

 mer, increasing frequency and intensity of winds from 

 the northeast produce a surge reaching the bottom at 

 the Lee Stocking Island study site in the fall (Caribb. 

 Mar. Res. Cent., Vero Beach, FL 32963, unpubl. data). 

 The significance of wave disturbance is suggested 

 by our own anecdotal observations of short-term de- 



creases in reproductive activity concurrent with 1-2 

 day periods of reduced temperature and increased 

 surge which occurred during the survey periods in early 

 summer. Reductions in reproductive activity with in- 

 creasing water turbulence have been noted for queen 

 conch in the Caicos Islands (Davis et al. 1984) and for 

 milk conch Stromhus costatus in Puerto Rico (R.S. 

 Appeldoorn, Dep. Mar. Sci., Univ. Puerto Rico, Maya- 

 guez, PR 00709, pers. commun.. May 1990). 



As with temperature, photoperiod may influence the 

 production of mature gametes or have a direct effect 

 on the behavior of conch. It is likely that the combina- 

 tion of increasing water temperature, coupled with in- 

 creasing length of day, triggers the mass migration of 

 adult conch from hardground to sand habitats and to 

 search for mates. Decreasing length of day and increas- 

 ing wave surge appear to provide the best explanation 

 for termination of the reproductive season, as pairing 

 and copulation ended while bottom-water temperature 

 was high. Experimental analysis will be required to 

 determine the mechanisms involved in seasonal re- 

 productive rates. Temperature, rates of temperature 

 change, photoperiod, physical turbulence, and other 

 seasonally variable environmental factors will need to 

 be considered. 



Similar to the findings of several others (D'Asaro 

 1965, Robertson 1959, Brownell 1977), egg-laying oc- 

 curred primarily on clean coral sand with coarse grain 

 size. Davis et al. (1984) noted that this type substrate 

 may be critical for reproductive activity. Copulation 

 and spawning stopped when they placed conch on a 

 bottom type other than coral sand. At Lee Stocking 

 Island, mating on hardbottom was observed, but was 

 rare. Given that only one egg mass was found on sub- 

 strate other than coral sand, it is clear that this is the 

 preferred, if not critical, substrate for egg-laying. 



This study provides the first report on abundance and 

 distribution of queen conch veligers in the field. Veli- 

 gers were present in the water column from 2 June to 

 the end of September, in concordance with relatively 

 constant rates of egg-laying from April through Aug- 

 ust. Despite a spawning season spanning 7 months, 

 high numbers of larvae were present in the two inlets 

 only during a 2-month period (July and August). 



Although mechanisms involved in seasonality of 

 larval production and survival are unknown as yet, it 

 is clear that larvae were most abundant during the 

 period of warmest water conditions. Summer spawn- 

 ing in Exuma Sound has adaptive significance. First, 

 high temperatures are associated with higher develop- 

 mental rates in pelagic larvae (Thorson 1950, McEd- 

 wards 1985, Boidron-Metairon 1987), decreasing the 

 time larvae spend in the plankton and probably reduc- 

 ing larval mortality (Strathmann 1980). However, in- 

 crease in temperature needs to be coupled with a food 



