Ecological geography of the hawksbill turtle (Eretmochelys imbricata) in the West Atlantic

Peter Meylan^1*F. Alberto Abreu-Grobois²Anne Meylan^3,4Beth Brost⁴Whitney Bullock¹Genaro Castillo⁵Liza J. Conrad¹Denise Flaherty¹Arcelio Gonzalez Hooker⁵Jennifer Gray⁶Cristina Ordoñez⁵Sue Schaf^4,7Kaj Schut⁸Ximena Velez-Zuazo⁹

• ¹Natural Sciences, Eckerd College, St. Petersburg, United States
• ²Universidad Nacional Autonoma de Mexico Instituto de Ciencias del Mar y Limnologia Unidad Academica Mazatlan, Mazatlan, Mexico
• ³Florida Fish and Wildlife Conservation Commission, Tallahassee, United States
• ⁴Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, Saint Petersburg, United States
• ⁵Sea Turtle Conservancy, Gainesville, United States
• ⁶Bermuda Zoological Society, Flatts, Bermuda
• ⁷Florida Fish and Wildlife Conservation Commission, Fish and Wildlife Research Institute, Marathon, United States
• ⁸Sea Turtle Conservation Bonaire, Kralendijk, Bonaire, Sint Eustatius and Saba
• ⁹Smithsonian Conservation Biology Institute, Front Royal, United States

Understanding the geographic distribution of genetic diversity of imperiled species across all life history stages and identifying the factors that shape those distributions are key to maintaining long-term genetic diversity and the health of populations. This knowledge is particularly important for highly mobile marine organisms, whose extensive movements can obscure patterns of population structure. We substantially expand the genetic dataset for the critically endangered hawksbill turtle, Eretmochelys imbricata, in the West Atlantic, focusing on the southwest Caribbean. Our dataset comprises nearly 3,000 mtDNA control region sequences (740 bp) assigned to 60 haplotypes: 41 found in rookeries and 47 in foraging grounds, including 17 orphan haplotypes. The Panama metapopulation represents a major center of genetic diversity for hawksbills, with one of the highest recorded diversity values for the species (h = 0.749, π = 0.00782), nine endemic haplotypes, and four additional haplotypes that are endemic to the Southwest Caribbean. Rarefaction analyses indicate that a sample size of at least 100 is necessary to reveal true haplotype richness at most rookeries. Many-to-many mixed stock analyses, incorporating rookery size and distance priors for 19 rookeries and 15 developmental foraging grounds, suggest that hatchlings from rookeries in the southwest Caribbean are distributed among multiple, widely-spaced foraging grounds across the West Atlantic. These results support a groups-to-soups analogy, in which genetic variability across foraging grounds represents a continuum of genetic diversity that can best be explained by a "current conveyor" model. The dataset shows that philopatry in hawksbills is not absolute, resulting in true biological dispersal and geneflow on local, regional, and ocean-basin scales, likely facilitated by dispersion during the epipelagic stage. The important contribution of oceanographic features to genetic variation at rookeries and foraging grounds is corroborated, as is the concept of oceanographic "dispersal shadows" that limit geneflow between rookeries. This study reinforces the assertion that all range states share responsibility for the recovery of the hawksbill, because foraging grounds, that are often at distant locations, are the source of future generations of reproductive adults. We also document significant movement by hawksbills between regional management units (RMUs) 29 and 30 in the West Atlantic.