Integrating Ecology, Natural History, and Regional Management for Conservation of Tropical Intertidal Gastropod Fisheries
- Author(s): Meyer, Erin Leigh
- Advisor(s): Hickman, Carole S
- et al.
Overexploitation and habitat alteration are pushing individual species toward extinction and may precipitate the collapse of entire ecosystems. Fishing pressure is continuing to increase in response to rising global demand and more efficient fishing technologies. To address anthropogenic impacts on marine ecosystems, management and conservation actions must be direct, strictly enforced, and adaptable. Priority should be allotted to those species that are highly visible and easily accessible, as these will likely experience extinction first. Invertebrates, in general, suffer from a lack of awareness and knowledge, which is exacerbated by the lack funding for basic research. The status of most invertebrate fisheries is unknown, and often the basic information required to develop management plans is lacking. Efforts and funding for marine conservation should thus be concentrated on invertebrate fisheries.
Molluscs account for nearly half of the reported, marine invertebrate catch worldwide. Although gastropods do not account for a large percentage of the catch, they play an important role in structuring rocky intertidal communities and are potentially important indicators of climate change. Cittarium pica (Linnaeus, 1758) is a large gastropod with a disjunct distribution in the Tropical Northwestern Atlantic. It is an important artisanal fishery throughout its range and is commercially harvested in only the U.S. Virgin Islands and Colombia. In the mid-1800s, C. pica was fished to extinction in Bermuda due to overharvesting. It was reintroduced to Bermuda in 1982, where it is currently fully-protected. Following analysis of population growth and expansion, along with documentation of the reintroduction protocol and subsequent monitoring, this reintroduction was determined to be a success (Chapter 4). The current level of fishing pressure on C. pica is explained by a combination of socioeconomic factors and marine conservation status, including human population density, level of affluence, management rank, and coverage of marine protected areas (MPAs) (Chapter 1). Countries with a higher management rank do have lower fishing pressure, which suggests that management regulations have a positive affect on the population of C. pica, as expected. In contrast, countries with high coverage of MPAs have higher fishing pressure on C. pica. This is most likely because the majority of MPAs within the territories and countries included in this study do not extend into the rocky intertidal habitat. Thus, understanding the interactions between socioeconomic motivations for fishing and marine conservation metrics is an important step in evaluating fishing pressure on and developing management plans for C. pica.
Understanding the socioeconomic motivation for harvesting the species and whether current management is adequate are not alone sufficient. To improve current regulations, predict population growth or decline, and to target locations for MPAs, knowledge and maps of the distribution of preferred habitat are needed. Cittarium pica inhabits the rocky intertidal mostly on windward shores. The distribution of rocky intertidal and other coastal habitats in Bermuda, where it was reintroduced, had not been assessed prior to this project. High-resolution imagery was used to generate maps of the intertidal habitats of Bermuda, which indicate that most of the coastline of Bermuda consists of rocky intertidal (Chapter 2). The population of C. pica in Bermuda is projected to expand because much of the windward rocky shores are currently unoccupied. The distribution of C. pica on a local scale (within sites) is affected by the unique biological diversity and geomorphological complexity of the rocky intertidal (Chapter 3). Although extensive research has addressed community structuring in the rocky intertidal, visualization of distribution patterns on geomorphological structures is largely ignored or oversimplified. Geomorphological and topographic complexity influence local scale distributions of species and thus the broad-scale patterns. Intertidal zonation of C. pica is habitat-specific, illustrating weak zonation by size only within sites with low wave action and medium vertical relief. Classifying the rocky intertidal into habitat categories contributes to a new understanding of the observed zonation patterns. Because range boundaries of rocky intertidal species at high latitudes have reacted quickly to environmental conditions, species in the rocky intertidal may be useful as indicators of climate change and its impacts. Thus, documenting and interpreting the current distribution of rocky intertidal organisms is increasingly important.
Cittarium pica is a non-commercial, artisanal fishery throughout the Tropical Northwestern Atlantic, except in a few locations. It is managed in six territories and countries in the region, even though management is needed throughout. The species has also recently entered the aquarium trade, so exploitation rates are only going to continue to increase. To combat the high (and growing) demand for C. pica, I recommend developing a multi-faceted management plan, including maximum harvest size (1-gallon per day, per person), minimum landing size (62 mm), seasonal closure of the fishery (variable by location), and establishment of marine protected areas targeting the rocky intertidal habitat. Enforcement is of extreme concern, so involvement of the local fishers, community, and other stakeholders is vital throughout the process of development and implementation of management plans.