Ecology And Management Of The West Indian Topshell Cittarium Pica (l) (gastropoda: Trochidae) Of The Exuma Islands, Bahamas

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Biology and Living Resources


The West Indian topshell, Cittarium pica (L.), is fished throughout its range. While the need for management of the snails' fisheries has been indicated, this large, rocky-intertidal species has remained ecologically poorly known. In this study, aspects of the population dynamics of unexploited Bahamian stocks from the Exuma Land and Sea Park were quantified so as to recommend size limits for management in terms of maximum yields.Population size-frequency data and tag-release experiments demonstrated that at high wave-stress sites, natural mortality was highest while growth rates were lowest. Population densities of Cittarium and its gastropod predators were highest at high wave-stress sites. High Cittarium abundance and small average size at these sites indicate higher levels of recruitment than at low wave-stress sites. Total edible biomass was most concentrated in high wave-stress habitat but spawnable biomass was not, due to low fecundity. The high habitat and site dependence of the topshell's ecology demonstrate complexities to be expected in reaching sound management understanding for other similarly sedentary invertebrates. Spawnable biomass and snails larger than the minimum commercial size of 60 mm were most abundant at scattered sites of optimal habitat on intermediate wave-stress coasts. Such sites, possibly of special importance for regional stock maintenance are also targeted for harvest in fished stocks.High catchability and other aspects of the topshell's biology and fisheries indicated size limitation as the most effective management option available. Minimum size of capture for maximum yield-per-recruit at high fishing mortality differed greatly between habitat types. A single, 70-mm minimum size of capture is recommended for management purposes since it will maximize yields at the commercially targeted sites. With proper enforcement this size limit would only ensure regional protection of between about 45% and 75% of the potential unexploited-stock spawn production. With significant fishing at smaller sizes, much less spawn potential is protected and Cittarium stocks may thus easily experience recruitment overfishing.


Biology, Oceanography; Agriculture, Fisheries and Aquaculture

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