The Fishery and Ecology of Cittarium pica in the West Indies

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MacFarlan, Reuban James-Allen
thesis / dissertation description
Cittarium pica, the West Indian Top Shell or “whelk,” is an understudied but culturally and ecologically important intertidal gastropod in the Caribbean. The species faces overexploitation and possible extirpation in much of its range due to a confluence of factors including life-history traits, a diffuse artisanal fishery, and lack of basic scientific knowledge. The undocumented, unregulated, and unreported nature of artisanal and small-scale commercial harvesting of this species renders its study quite different from that of other more recognizable species such as conch or spiny lobster. Here I have compiled four manuscripts that address specific questions related to the ecology and fishery of whelks in contemporary, historic, and pre-historic time periods. The first chapter addresses whether there is variation in shell shape and attachment strength related to sea conditions. The second and third chapters are sequential and in chapter 3 I first decouple the contributions of harvesting and wave exposure as drivers of size and abundance of whelks. The second part of that study expands the number of sites, introduces land development as a factor and tests the confounding roles of harvesting, waves, or and development in structuring size and abundance of whelks. In the final manuscript I describe how whelks have been impacted by exploitation pressure during three different occupations of coastal people in the past 1500 years. Based on shell materials excavated from pre-Columbian and colonial era middens I rebuild present a simple time series of body size and abundance metrics to contrast with contemporary size distributions from manuscripts two and three. This collection of projects has been multidisciplinary and involved fisheries science, marine ecology, and zooarchaeological techniques. Field research was conducted in the British Virgin Islands and Puerto Rico where intertidal surveys and experiments were performed on live whelk along with the processing of archaeological faunal remains. I found that whelks on wave-exposed shores have greater attachment strength and shorter more compact shells than on sheltered shores. I determined that access by fishers to sites was by far the most potent selective factor in structuring the size and abundance of whelks in the region and likely contributing to the general perception that the species is in decline. And in the final chapter I infer, based on the body size and abundance of whelk specimens from middens, that exploitation histories vary substantially through space and time in the archaeological record.