Population Composition of an Exploited Hawaiian Fishery
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Overharvesting has been implicated in altering the population structure of marine organisms, reducing genetic diversity and adaptive capacity. Overharvested fisheries can be particularly vulnerable to environmental and anthropogenic stressors due to the loss of advantageous mutations. The Hawaiian broadcast-spawning limpet, Cellana exarata, is subject to varying levels of harvesting pressure on different islands, ranging from no harvest on the uninhabited island of Nihoa in the Papahānaumokuākea Marine National Monument, to a reduction in population density on Maui and Kaua‘i, to near extirpation on O‘ahu, the most populous of the Hawaiian Islands. In this study, we use genome-wide surveys of genetic variation (ezRAD, >21,000 loci) on C. exarata from the islands of Nihoa, Kaua‘i, Maui, O‘ahu, and Hawai‘i to test for relationships between genetic diversity, population size, island age, and harvest pressure. Global estimates of genetic differentiation among islands are greater than those estimated with mtDNA. Pairwise comparisons among islands indicate a substantial difference in genetic composition between the inhabited Main Hawaiian Islands and the uninhabited island, Nihoa. Estimates of nucleotide diversity (π) were greatest on Nihoa (π = 2.05 × 10−3), despite having the smallest estimated population size (without harvesting); estimates of nucleotide diversity on the Big Island of Hawai’i are the lowest of all the islands in this study (π = 1.71 × 10−3), despite having the largest estimated population size. This difference in genetic diversity, while initially counter intuitive, is correlated with island age and indicates that C. exarata populations within the MHI experienced a recent bottleneck. Overall, these results suggest that the PMNM harbors a stockpile of genetic diversity for C. exarata, despite relatively small population sizes when compared to the MHI.
Cockett, Patricia Malamalama (2015). Population Composition of an Exploited Hawaiian Fishery. Master's thesis, Texas A & M University. Available electronically from