Evidence of Survival Value Related 

 to Burying Behavior In Queen 

 Conch Strombus gigas 



Edwin S. Iversen 

 Scott P. Bannerot 



Division of Marine Biology and Fisheries 



Rosenstiel School of Marine and Atmospheric Science, University of Miami 



4600 Rickenbacker Causeway. Miami, Florida 33149-1098 



Darryl E. Jory 



Centre de Investigaciones Cientfficas, Universidad de Oriente, Nucleo de Nueva Esparta 

 Boca de Rio, Apartado 147, Porlamar, Isia de Margarita, Venezuela 



Interest in queen conch Strombus 

 gigas aquaculture and more efficient 

 management of fished stocks has in- 

 creased due to the declining catches 

 of this species throughout its range 

 (Brownell and Stevely 1981). lOiowl- 

 edge of conch survival is critical to the 

 success of extensive and intensive 

 aquaculture, and also to management 

 of the exploited stocks. Information 

 on survival, including predation rates 

 during the period after larval conch 

 have left the planktonic (drifting) 

 stage and settled onto the bottom un- 

 til the time they emerge and graze 

 about on the bottom, is very limited. 

 Despite field searches conducted by 

 numerous researchers in different 

 areas, very few small conch (< 1 year- 

 old; ~5 cm in length) have been found 

 in nature (Robertson 1959, Randall 

 1964, Hesse 1979, Davis and Hesse 

 1983). Research by Iversen et al. 

 (1986) in the Berry Islands (Bahamas) 

 using a variety of devices to sample 

 the substrate and the substrate-water 

 interface confirmed the paucity of 

 young conch on or near the substrate 

 surface in areas adjacent to aggi-ega- 

 tions of > 1-year-old juveniles. It 

 seems reasonable that these very 

 young conch do not migrate over 

 long distances to the cays where we 

 find the large juveniles, but are car- 

 ried during their planktonic life by 

 currents to these locations. These 

 findings suggest that conch may be 



buried almost continuously until 

 they reach a shell length of ~5 cm. 

 The purpose of this study is to use 

 tag-recapture data to examine the 

 relationship between survival of juve- 

 nile conch and their burying activity. 



Methods and materials 



The data used in this study were col- 

 lected in the Berry Islands (Bahamas) 

 about 190 km east of Miami, Florida 

 (Fig. 1). A wide range of conch sizes 

 (3.5-22.0 cm) was tagged during 

 these exTDeriments at all seasons and 

 at several different cays to account 

 for the effects of different habitats, 

 conch sizes, and seasonal variation. 



The sampling area, consisting of 

 shallow sand flats with abundant 

 turtle grass Thalassia testudinum, 

 is described in more detail by Iver- 

 sen et al. (1987). 



Individual conch were tagged with 

 thin, numbered plastic tags affixed 

 to the spire vdth underwater epoxy. 

 Shell length was taken using a mea- 

 suring board (Iversen et al. 1987). 

 Shallow intertidal waters were sam- 

 pled by wading and the deeper off- 

 shore water by snorkeling. Counts 

 of tagged conch were made on 23 

 sampling trips lasting 4-5 days made 

 approximately every 5 weeks be- 

 tween May 1980 and February 1983. 

 A conch was considered to be buried 

 when it was not found on one or 



more sampling trips, but was found 

 alive on subsequent visits (Table 1). 

 We believe this to be a reasonable 

 assumption, because the aggrega- 

 tions of conch we studied remained 

 in close proximity to the cays and 

 when not buried were easOy located. 

 Conchs as large as 10-15 cm in length 

 which we placed in 25-m2 pens 

 would bury and were not found on 

 some visits despite intensive search- 

 ing. On subsequent visits a month 

 or more later, they would reappear 

 on the surface of the substrate. For 

 example, of 27 tagged conch in one 

 pen, seven were buried on at least 

 one visit between April and Decem- 

 ber 1980. Tagged individuals released 

 at various cays that were not subse- 

 quently found were considered to 

 have fallen prey to predators; large 

 juveniles (^16 cm) were assumed to 

 have migrated offshore to deep 

 water (Iversen et al. 1987). 



Results 



Our tagging data show a significant 

 positive correlation (Fig. 2) between 

 survival and percent buried for conch 

 released in the subtidal region of 

 about-2 m depth south of Vigilant 

 Cay (shell length range, SLR, 3.5- 

 16.5 cm; r = 0.80; P<0.01), and for 

 conch from intertidal zones at Cat 

 Cay (SLR 4.5-18.0 cm; r = 0.56; 

 P<0.05) and Little Cockroach Cay 

 (SLR 8.0-22.0 cm; r = 0.81; P<0.05). 



Discussion 



Predation is probably the most im- 

 portant cause of natural mortality 

 on stocks of > 1-year-old juvenile 

 conch. Based on our searches for 

 parasites in juveniles and adult 

 conch, and our field observations, 

 we do not believe that parasites or 

 diseases play an important role in 

 conch survival. There are reports of 

 isolated mass mortalities of conch 



Manuscript accepted 28 December 1989. 

 Fishery Bulletin, U.S. 88:383-387. 



383 



