AbStfclCt.— Habitat association, 

 growth, and burrowing behavior 

 were examined for a population of 

 young-of-the-year juvenile queen 

 conch, Strombus gigas L., in the 

 southern Exuma Cays, Bahamas, 

 during the winter 1988-1989. These 

 early juveniles (35-54 mm siphonal 

 shell length) primarily inhabit shal- 

 low unvegetated zones where they 

 burrow in the sediment during the 

 day and surface at night. Labora- 

 tory experiments showed that the 

 burrowing rhthym was endogenous. 

 Highest densities of 1- and 2-year- 

 old juveniles (80-140mm) conch 

 were observed in adjacent, deeper 

 seagrass beds, suggesting that queen 

 conch make an ontogenetic shift in 

 habitat. Results of an enclosure ex- 

 periment revealed that growth rates 

 of early juvenile conch were higher 

 in seagrass (0.11 mm/day) and in 

 rubble (0.09 mm/day) than in bare 

 sand (0.01 mm/day I where they were 

 initially found. These observations 

 suggest that emergence of juvenile 

 conch and movement to vegetated 

 habitats at 35-54 mm shell length 

 is associated with changes in nutri- 

 tional requirements. Changing habi- 

 tat association with age may also be 

 related to predator avoidance and 

 burrowing capabilities. Habitat re- 

 quirements of early juvenile conch 

 are different from those of 1-year- 

 old juveniles and stock enhancement 

 programs will need to consider on- 

 togenetic habitat shifts. 



Ontogenetic shift in habitat by 

 early juvenile queen conch, 

 Strombus gigas: patterns and 

 potential mechanisms 



Veronique J. Sandt 

 Allan W. Stoner* 



Caribbean Marine Research Center 



805 E 46th Place 



Vero Beach. Florida 32963 



Manuscript accepted 6 April 1993 

 Fishery Bulletin 91:516-525 (1993) 



Declining populations of queen conch 

 (Strombus gigas L. ), usually attrib- 

 uted to overfishing, have been re- 

 ported for numerous areas in the 

 Caribbean region (Brownell and 

 Stevely, 1981; Appeldoorn et al., 1987; 

 Berg and Olsen, 1989). Hatchery pro- 

 duction and field release of juvenile 

 conch have been suggested as a 

 means of restoring depleted stocks 

 (Berg, 1976; Brownell, 1977; Davis 

 and Hesse, 1983; Iversen et al, 1986) 

 but release methods have not been 

 perfected (Stoner, unpubl. data). Al- 

 though survival in small juvenile 

 conch is low in natural populations 

 (Appeldoorn, 1984), mass rearing of 

 large juveniles (1- and 2-years-old) 

 is costly (Siddall, 1983) and releases 

 will need to be made with 0+ year 

 class conch. Unfortunately, pilot re- 

 leases of small conch have resulted 

 in very low survival (Appeldoorn and 

 Ballantine, 1983; Siddall, 1983; 

 Appeldoorn, 1985), probably because 

 of the lack of ecological information 

 on early stage juveniles and problems 

 associated with the identification of 

 suitable habitats (Iversen et al., 1986; 

 Stoner and Sandt, 1991; Stoner, 

 unpubl. data). 



Despite high densities (1— 2/m 2 ) of 

 1- and 2-year old conch (80-140 mm 

 shell length) in certain seagrass 

 meadows (Alcolado, 1976; Weil and 

 Laughlin, 1984; Stoner and Waite, 

 1990; Wicklund et al, 1991; Stoner 

 et al., 1993), individuals less than 



50-60 mm in shell length (called 

 early juveniles in this study) have 

 rarely been seen in the field. Iversen 

 et al. (1986) suggested that these 

 early juvenile conch probably spend 

 a large part of their time buried in 

 the sediment. Attempts have been 

 made to find them using suction 

 dredges (Iversen et al., 1987; Stoner, 

 unpubl. data) but few early juveniles 

 have been collected and, to date, no 

 quantitative data exist. 



An opportunity to gather informa- 

 tion on the distributional ecology and 

 behavior of early juvenile queen 

 conch was provided by the fortuitous 

 discovery of a 0+ year class popula- 

 tion near Neighbor Cay, in the cen- 

 tral Bahamas, in January 1989. 

 The subsequent investigation was 

 designed: 1) to quantify habitat- 

 specific distribution and abundance 

 patterns, 2) to examine habitat- 

 specific growth rates, and 3) to ex- 

 amine buiTowing behavior in relation 

 to time of day and light cues. The 

 findings are discussed in terms of 

 stock rehabilitation and management. 



Study site 



The distribution and behavior of 

 early juvenile queen conch was in- 

 vestigated near the north shore of 



*To whom correspondence should be ad- 

 dressed. 



516 



