164 



Fishery Bulletin 90|l). 1992 



Figure 3 



(A) Bottom- water temperature at 17 m depth 

 with 7-day averages (soHd line) and photo- 

 period in number of hours between sunrise 

 and sunset (dashed line). (B) Number of 

 queen conch Strombus gigas females on 

 sand engaged in various reproductive activ- 

 ities. (C) Number of conch larvae in Rat Cay 

 and Adderley Cay passes, January 1988- 

 February 1989. 



30 minutes; 7-day averages were 

 generated and plotted (Fig. 

 3A). Surface-water temperature 

 and weather conditions were re- 

 corded each time that plankton 

 was collected. 



To examine potential correla- 

 tion between reproductive sea- 

 sonality and photoperiod, a year- 

 long photoperiod curve (Fig. 3A) 

 was constructed for the study 

 site. Numbers of hours and min- 

 utes between sunrise and sunset 

 were calculated for local latitude 

 at 9-day intervals using the Nau- 

 tical Almanac. 



Plankton collections 



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 29 

 28 

 27 

 26 

 25 

 24 

 23 



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FMAMJJ A SO NDJF 



-•ADDERLEY CUT 



-O RAT ISLAND "? 



Daytime plankton collections 

 were made for queen conch veli- 

 gers from mid-March to October 

 1988. For seasonal analysis of 

 larval abundance, collections 

 were made every 2 to 3 weeks in 

 the pass between Lee Stocking 

 Island and Adderley Cay (Adder- 

 ley Cay cut) and in the pass be- 

 tween Rat Cay and Children's 

 Bay Cay (Rat Cay cut) (Fig. 1). 

 Additionally, collections were 

 made over the area surveyed for 

 reproductive activity (Reproduc- 

 tive Site) with the primary pur- 

 pose of detecting low densities of conch larvae at the 

 onset and end of the reproductive season. Collections 

 were not made at the Reproductive Site during peak 

 reproduction, between July and mid-August. To ex- 

 amine densities and size-frequency of larvae on Exuma 

 Bank, four collections were made over a known nursery 

 for S. gigas, west of Children's Bay Cay (Fig. 1). This 

 site is approximately 3.4 m deep and vegetated with the 

 seagrass Thalassia testudinum. 



•m» « i» I 



c 



—1 1 r- 



FMA MJ JA SON DJF 



1988 1989 



MONTH 



In the passes, plankton were sampled during the first 

 2 hours of the flood tide; on the bank, tows were 

 scheduled during the last 2 hours of flood tide. Plankton 

 collections were made by tovvang a 0.5m diameter con- 

 ical net, 5 m long, with 202 ^m mesh. Two tows were 

 made at each site. Because the location of larvae in the 

 water column was unknown, collections at the Repro- 

 ductive Site were made by towing the net at 9 m depth 

 (midwater column) for 10 minutes, then raised near 



