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    AES Gruber III

    2021-07-21   13:45 - 14:30

    Moderator: Marcus Drymon

    1.  13:45  IN-PERSON    Delineation of Blacktip Shark Genetic Stock Structure in the Northern Gulf of Mexico. Dominic Swift*, Texas A&M University-Corpus Christi; Shannon O'Leary, Saint Anselm College; Dean Grubbs, Florida State University; Bryan Frazier, South Carolina Department of Natural Resources; Jayne Gardiner, New College of Florida; Marcus Drymon, Mississippi State University; Dana Bethea, NOAA Fisheries; David Portnoy, Texas A&M University-Corpus Christi

    The blacktip shark (Carcharhinus limbatus) is a large coastal shark distributed throughout the western North Atlantic Ocean and Gulf of Mexico. In U.S. waters, blacktip sharks are managed as Atlantic and Gulf stocks, but catch quotas in the eastern and western Gulf sub-regions vary by close to an order of magnitude. In general, appropriate management increases sustainability and long-term persistence of exploited stocks by limiting localized overfishing which can lead to population collapse and loss of adaptive genomic variation. Blacktip shark females are thought to faithfully return to coastal sites within their region of birth for parturition, known as regional philopatry, which could limit dispersal and gene flow while enabling the sorting of localized adaptive variation. Population genomic approaches can inform fisheries management by describing the spatial partitioning of genomic variation to facilitate genetic stock delineation. These approaches also enable assessment of the relationship between environment and putatively adaptive variation, as well as robust identification of close-kin that are often used to infer philopatric behavior. We sampled more than 300 young-of-the-year blacktip sharks from coastal sites throughout the northern Gulf of Mexico to delineate stock structure among the eastern and western sub-regions. We examined genomic variation among sites and sub-regions, assessed for sibship and genomic diversity within sites, and investigated associations between environmental parameters and portions of genomic variation. Our results suggest the presence of two genetically distinct stocks which have implications for management of the blacktip shark and other coastal sharks in U.S. waters of the Gulf of Mexico.

    2.  14:00  VIRTUAL    Map-like Use of Earth’s Magnetic Field in Sharks. Bryan Keller*, Florida State University Coastal and Marine Laboratory; Nathan Putman, LGL Ecological Research Associates; R. Dean Grubbs, Florida State University Coastal and Marine Laboratory; David Portnoy, Marine Genomics Laboratory, Texas A&M University; Timothy Murphy, Florida State University, National High Magnetic Field Laboratory

    Migration is common in marine animals, and use of the map-like information of Earth’s magnetic field appears to play an important role. While sharks are iconic migrants and well known for their sensitivity to electromagnetic fields, whether this ability is used for navigation is unresolved. We conducted magnetic displacement experiments on wild-caught bonnetheads (Sphyrna tiburo) and show that magnetic map cues can elicit homeward orientation. We further show that use of a magnetic map to derive positional information may help explain aspects of the genetic structure of bonnethead populations in the northwest Atlantic. These results offer a compelling explanation for the puzzle of how migratory routes and population structure are maintained in marine environments, where few physical barriers limit movements of vagile species.

    3.  14:15  VIRTUAL    Caught On The Net: Quantifying the Online Trade of a CITES-Listed Elasmobranch. Jennifer Pytka*, Bangor University; Adel Heenan, Bangor University; Alec Moore, Bangor University

    Sustainable wildlife trade provides vital support to human communities but unregulated trade has led to increased global extinction risks for many taxa of plants and animals. Despite national and international regulation, endangered and protected species continue to be traded illegally and at unsustainable levels. Online research methods are increasingly used in conservation science to monitor illegal online trade, collecting data for neglected markets, countries, and species, but elasmobranchs continue to be largely ignored from studies on trade, outside fins and meat. The shark-like rays (Rhinopristiformes) are among the most threatened species of marine fishes and prized for their high value fins, but other uses for their derivatives is largely unrecognised in the literature. The bowmouth guitarfish (Rhina ancylostoma,Rhinidae) is characterized by ridges of enlarged thorns, which are sold as amulets for cultural and spiritual purposes. Until now, the market for their thorns has been ignored and undocumented. Using systematic online searches, we found a significant quantity of thorns for sale, often marketed as amulets, overwhelmingly based in Thailand where trade is prohibited. Here we used unobtrusive and accessible research methods which can be applied internationally and across species. Continued monitoring of online platforms can illuminate trade patterns essential for informing policy, and data from such studies can fill critical gaps needed to inform species-specific management plans.

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