DRILLING, SNATCHING, AND CONCHSERVATION: ASSESSING PREDATION OF QUEEN CONCH BY OCTOPUS USING DRILLING FREQUENCIES

Queen conch, (Lobatus gigas), has been a major emphasis of conservation initiatives withinThe Bahamas. To demonstrate the utility of using drilling traces for estimating the impact ofoctopus predation on queen conch, we looked at the drilling rates of infaunal juveniles (3-5 cmin length) and epifaunal juveniles (6-12 cm in length). Results from our preliminary data,based on shells representing 27 infaunal juveniles, and 21 epifaunal individuals, collected from2015-17 on San Salvador Island, indicate an important trend. First, infaunal individuals hadan octopi drilling frequency of 0.074. Other drilling traces can be attributed to naticids (0.037)and muricids (0.111). For epifaunal indiviudals, the successful octopus drilling frequencyincreases to 0.381 successfully drilled individuals and 0.143 for individuals with aborted drilling by octopi. Muricid drilling frequency was 0.238. Clearly, once infaunal juveniles move into the cohort of epifuanal juveniles, they are subject to high rates of predation by drilling molluscan predators. Rates of drilling calculated by the shells from this study, obtained from strand deposits, present a better estimation of predation by octopi in comparison to middens. Because marine species of hermit crabs quickly obtain discarded, predated gastropod shells, the frequency of conch shells associated with middens is skewed. Drilling can be used as a signal, or proxy, for estimating predation of conch. However, these estimates are still low since we are not able to effectively estimate rates of predation of species that chip the shells (e.g. tulip shells), shell crushing predators, and harvesting of undersized conchs.