NOTES Iversen et al : Survival related to burying behavior in Strombus gigas 



385 



lOOi VIGILANT CAY 

 r = 0.80 

 N = 9 



80 



H 



w 

 u 



02 

 W 



60 



40 



20 



"20 40 60 80 



PERCENT SURVIVAL 



100 



Figure 2 



Relationship between Strongii.s gigas burying 

 activity and survival. Vigilant Cay: oi^shore, 171 

 conch tagged 3 October 1980; SLR 6.7-9.3 cm. Cat 

 Cay: 455 conch tagged 27 May 1980; SLR 8.9-19.1 

 cm. Little Cockroach Cay: 84 conch tagged 8 April 

 1981; SLR 9.2-15.5 cm. N = number of months 

 the experiment lasted. 



during the summer on tide flats when temperatures 

 reached extremely high levels (Weil and Laughlin 

 1984). 



In the few trials made to date, survival of hatchery- 

 reared small conch (2.0-7.0 cm in length) released in 

 different locations in the Bahamas and the Caribbean 

 has been extremely low. For example, in St. Croix, 



Coulston et al. (1987) reported that unprotected 

 juvenile conch did not survive. And in a small-scale 

 preliminary trial, Iversen et al. (1986) reported com- 

 plete mortality of 1.3-3.7 cm long, hatchery-reared 

 conch placed under protective screens laid on the 

 substrate and held in place by rocks. 



To fully interpret our results and put them in con- 

 text with what is known about mortality and predation 

 in juvenile queen conch, it is necessary to consider the 

 factors affecting both burying behavior and mortality/ 

 predation. Concerning the former, we first note that 

 very small conch are almost never found unburied. 

 Although emphasis of our research was on animals 

 larger than 5 cm in length, we searched for small conch 

 during all field trips. Of the 491 small conch (1-9 cm) 

 we found, all but a few (~3%; A''= 15) were buried, 

 some as deep as 20 cm, while others were barely 

 covered by broken shells and rubble in shallow depres- 

 sions on a large tidal flat. With only a few exceptions, 

 those found on the substrate were larger than ~5 cm. 



Iversen et al. (1987) showed significant differences 

 in burying activity within a tidal cycle at various sites 

 in the Berry Islands. Significantly more conch buried 

 on high tides than on low tides, which they suggested 

 may be a response to possible increased predator ac- 

 tivity during high tides when large swimming predators 

 can reach the upper intertidal zone. This apparent tidal- 

 height behavioral response should not be triggered in 

 the deeper (subtidal) water offshore of Vigilant Cay 

 where we released tagged conch. Our results showing 

 a relationship between survival and burying behavior 

 suggest that conch over a wide range of sizes are less 

 vulnerable to predation when buried. This may explain 

 why the highly vulnerable, thin-shelled young-of-year 

 bury for extended periods. 



In addition to the effects of conch size and tide stage, 

 burying behavior may be affected by time of year (a 

 proxy which encompasses a number of environmental 

 circumstances, such as water temperature and wind 

 and sea conditions). According to Hesse (1979), sea- 

 sonal variation in burying behavior is also a factor, with 

 more active burying during the winter when the waters 

 are cooler and the winds stronger than during the re- 

 mainder of the year. However, no clear-cut seasonal 

 trend in burying activity is evident from our data. 

 Rather, there are generally wide variations in the num- 

 ber of animals buried, which we believe are possibly 

 related to different environmental conditions in the dif- 

 ferent habitats of the cays where we collected our data. 

 Our size-frequency data suggest that burying activity 

 is not related to the size of the animals, after they at- 

 tain a shell length of ~5-6 cm. 



With respect to mortality, Appeldoorn (1985) showed 

 that juvenile queen conch mortality rates were highest 

 during summer and lowest during winter in Puerto 



