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Fishery Bulletin 92(2). 1994 



and not all free-ranging survivors were recovered. 

 High mortality of conch on tethers at site C2 was 

 probably a result of the low density of conch sur- 

 rounding the tethers, lack of protection provided by 

 enclosures, and reduced ability to avoid predators. 

 Where the density of ambient conch was high (site 

 CI), mortality rates in enclosures and on tethers were 

 nearly identical, suggesting the significance of alter- 

 native prey, already discussed. 



Comparisons of growth rates among experimental 

 treatments in this study are difficult to make because 

 of different times and durations of the growth peri- 

 ods. For example, high growth rates in free-ranging 

 conch calculated for April to September 1990 reflect 

 the high temperature season. Best comparisons are 

 provided by enclosure and tether experiments run 

 concurrently between April and June 1990, and by 

 growth rates for free-ranging and enclosed conch 

 measured between December 1990 and February 

 1991. In both cases the conch had relatively similar 

 growth rates within stock type and site, suggesting 

 that caging and tethering did not affect the nutri- 

 tional state of experimental animals. 



Given potential artifacts of enclosures and tethers 

 on survivorship, measurements made on free-rang- 

 ing conch will be preferred for certain questions, par- 

 ticularly those related to behavioral patterns and 

 natural mortality (as opposed to relative mortality 

 measured with tethers). On the other hand, it is im- 

 possible to recover all free-ranging conch and tag 

 recovery can not be translated directly into survi- 

 vorship. Mark-recapture data can be used to estimate 

 population changes, with certain inherent limitations 

 (Skalski and Robson, 1992); this may be a good ap- 

 proach for those primarily concerned with 

 survivorship in large outplants. Those more inter- 

 ested in the role of habitat, stocking densities, and 

 mechanisms of mortality will probably wish to main- 

 tain more control over the experimental animals. 

 Covered enclosures, such as those used by Ray and 

 Stoner (in press), offer the best means for testing 

 growth potential in different habitats; meanwhile teth- 

 ers give good information on relative rates of mortality 

 for comparison of different sites, conch sizes or types. 



Conclusions 



One of the most striking implications of Appeldoorn's 

 ( 1988) estimates of natural mortality in queen conch, 

 is that juvenile mortality is very high. For example, 

 survivorship in the first two years of life (to approx. 

 130 mm SL) may be as low as 35%. Our results on 

 recovery of free-ranging wild conch over a 7-month 

 period corroborate Appeldoorn's calculations. One 



may conclude from such survivorship curves that it 

 will take a very large number of seed conch to en- 

 hance a local stock size. The problem would be exac- 

 erbated by poor seed stock quality, releases in sub- 

 optimal habitats, or release procedures which place 

 the conch at unusual disadvantage (e.g. poor han- 

 dling and acclimation, season of release, stocking 

 density, and seed stock size). 



Success in enhancing molluscan populations with 

 hatchery-reared stocks has been variable. For ex- 

 ample, Tegner and Butler (1985) recovered only 1% 

 of their outplanted red abalone, Haliotis rufescens, 

 one year after release. With the same species, Ebert 

 (1989) reported high growth coupled with modest 

 survivorship and some individuals reached sexual 

 maturity with ripe gonads. In Japan, considerable 

 success has been documented with the ezo abalone, 

 Haliotis discus lannai (Saito, 1984). Hatchery-reared 

 bay scallops, Argopecten irradians, released into the 

 field at 20 mm were all lost within a month in one 

 year; however, in another year the scallops lived to 

 reproduce (Tettelbach and Wenczel, 1991). Despite 

 failures, success is usually achieved as a result of 

 adequate research. Stock rehabilitation via aquac- 

 ulture may be the only viable means of restoring 

 populations depleted to near-extinction levels, as is 

 the case for queen conch in some regions of the Carib- 

 bean (Appeldoorn et al., 1987; Berg and Olsen, 1989). 



Several steps will be required for restoration of 

 queen conch stocks in the field: 



1 The quality of hatchery-reared stock must be high 

 and consistent. Morphology, physiology, and be- 

 havior must be considered, and stock quality 

 should be field tested before major releases. Mod- 

 els of the effects of hatchery stock releases on a 

 fishery (e.g. Madenijian et al., 1991; Polovina, 1991) 

 will be useful only if hatchery-reared and wild stocks 

 are identical in growth and mortality. 



2 Sites for releases should be chosen with respect to 

 information on historically significant nursery 

 grounds, and preliminary tests for habitat suit- 

 ability must be run with juvenile conch of the sizes 

 to be seeded. 



3 Release techniques must be developed to optimize 

 conch survivorship. Factors which require further 

 research are animal size, stocking density, mini- 

 mum numbers to be released, release timing (sea- 

 son and time of day), and animal handling and 

 acclimation. High numbers of individuals will need 

 to be released given natural mortality rates and 

 success might be improved by making releases at 

 several sites. 



4 Released conch and natural stocks will need to 

 be managed in a comprehensive, multidisciplinary 



