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Fishery Bulletin 92|2). 1994 



ery-reared and 30 wild conch (tagged individuals) at 

 each outplant site. Burial frequency was quantified 

 as the percentage of conch that had at least part of 

 the shell buried in the sediment, detritus, or algae. 

 Counts for the two sites were pooled for each of the 

 conch types. General observations on locomotory ac- 

 tivity were also recorded. 



Data from the tag recovery surveys provided in- 

 formation on the movements of free-ranging conch. 

 During each tag recovery the type (wild or hatchery- 

 reared), initial site of transplant (CI or C2), and 

 number of tagged conch found in different regions 

 around the initial release sites (Fig. 2) were recorded. 

 The total number of conch found in each survey was 

 used to calculate the percentage of hatchery or wild 

 conch from site CI or C2 in each area surveyed. 



Enclosure experiments 



Experiment I Enclosure experiments were designed 

 to determine the significance of density-dependent 

 growth and survival of hatchery-reared and wild 

 conch in identical habitats. The first 3-month experi- 

 ment was conducted from 7 April to 9 July 1990. At 

 each site (CI and C2) 12 circular pens (30 cm high, 

 20 m 2 ) without covers were constructed of vinyl 

 coated wire mesh (2.5 x 5.0 cm). Prior to the experi- 

 ment (23 February-12 March) three haphazardly 

 placed 25 x 25 cm quadrants per cage were sampled 

 for Thalassia testudium components to ensure habi- 

 tat similarity among the pens, both within and be- 

 tween stations. In each quadrant, seagrass shoot den- 

 sity was estimated, and all above-ground parts were 

 collected into 3-mm mesh nylon bags. Living blades 

 and detritus were separated in the laboratory, dried 

 at 80°C and weighed. Detritus measurements were 

 made again at the end of the experiment (9-13 July 

 1990) to test for potential depletion of this impor- 

 tant food source. 



At each site tagged hatchery and wild conch were 

 placed in pens at three different densities, in two 

 random blocks. Stocking densities, spanning the high 

 range of natural densitites in the wild, were 0.5, 1.0, 

 and 2.5 conch-m -2 (10, 20, 49 conch-pen -1 ). The size 

 ranges for hatchery-reared and wild conch were 90- 

 109 mm SL (mean=100, SD=3) and 92-115 mm SL 

 (mean=102, SD=3), respectively. Before stocking the 

 pens with experimental conch, all visible epibenthic 

 predators such as tulip snails, Fasciolaria tulipa, 

 apple murex, Murex pomum, and the giant hermit 

 crab, Petrochirus diogenes, and sea urchins Trip- 

 neustes esculentus were removed. Every two weeks 

 throughout the experiment, dead conch were replaced 

 to ensure constant density; replacements were not used 

 in growth and survivorship measurements. 



Cumulative mortality was calculated by subtract- 

 ing the number of live conch remaining from the ini- 

 tial loading number. Mortality was examined statis- 

 tically at the midpoint (day 37) and at the end (day 

 93) of the experiment. Shell length was measured at 

 the start, near the middle (day 37), and at the end 

 (day 93) of the experiment, and growth rates were 

 calculated for the two periods. 



Experiment II A second 3-month enclosure experi- 

 ment was conducted at sites CI and C2 to compare 

 survival and growth of hatchery-reared and wild 

 conch in the winter (29 November 1990-21 Febru- 

 ary 1991). Enclosures built for experiment I were 

 reused in this experiment after having been clear of 

 conch since July 1990. Four enclosures at each site 

 were stocked with 10 hatchery-reared and 10 wild 

 conch (1.0 conch-m -2 ) gathered from the surround- 

 ing free-ranging populations. This density was cho- 

 sen because highest mean growth rates frequently 

 occurred at this density in enclosure experiment I. 

 The initial size of the hatchery-reared conch ranged 

 from 104-130 mm SL (mean=118, SD=5) and the wild 

 conch ranged from 109-134 mm SL(mean=122, SD=5). 

 Dead conch were replaced with similar sized free- 

 ranging conch every two weeks. As in the first ex- 

 periment cumulative mortality and growth rates 

 were determined only for the original stock, not the 

 replacements. Mortality was calculated five times 

 throughout the experiment, and analyzed statisti- 

 cally at the midpoint (day 35) and end (day 84) of the 

 experiment. Growth rates were calculated for two 

 growth periods, 29 November 1990 to 3 January 1991 

 and 3 January to 21 February 1991. 



Tether experiments 



Experiment I The first three-month tethering ex- 

 periment was conducted during the summer ( 12 April 

 to 11 July 1990) at sites CI and C2 to examine 

 survivorship, tag effects, and growth rates. The size 

 ranges for hatchery-reared and wild conch were 82- 

 116 mm SL (mean=100, SD=9) and 89-115 mm SL 

 (mean=101, SD=6), respectively. Each conch was se- 

 cured to a 0.5-m long stainless steel welding rod by a 

 1 m length of 20-lb test monofilament line that was 

 attached to the shell spire with a clear nylon cable 

 tie. The tether rods were marked with uniquely num- 

 bered tags and pushed 40 cm into the substratum 

 approximately 2 m apart. Conch were tethered in 

 four rows of 20 individuals. Each row contained 10 

 hatchery-reared conch and 10 wild conch in an al- 

 ternating pattern. For each type of conch, the shell 

 of every second individual was tagged to determine 

 potential tagging effects on conch mortality in the 

 free-ranging experiment. 



