Session 4: AES Gruber IRoom: Conference Theater2022-07-28 13:30 - 14:45 |
| Moderator: Michelle Passerotti |
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1. 13:30 Migratory Patterns of Female Blacktip Sharks, Carcharhinus limbatus, in the Western North Atlantic Ocean. Beth Bowers*, Florida Atlantic University; Bryan S. Frazier, South Carolina Dept. of Natural Resources; Stephen M. Kajiura, Florida Atlantic University mebowers5@gmail.com
The migratory pattern of blacktip sharks as reconstructed from the literature is inconsistent with the described range of this species. While the range extends to Massachusetts, the migratory pattern is thought not to surpass Cape Hatteras, NC. In the western North Atlantic Ocean, blacktip sharks overwinter off southeastern Florida in dense aggregations comprised almost exclusively of males. Sexual segregation is common in elasmobranchs and since females bear the energetic burden of reproduction, they may require different habitats and prey items than males, which may lead to different migratory patterns. Female blacktip sharks exhibit a synchronous, biennial reproductive cycle in which one year of reproduction is followed by a year of rest. Thus, migratory patterns may also differ between gravid and resting females. We tracked 36 female blacktip sharks using acoustic telemetry and used ultrasound to determine the reproductive state for 9 individuals. We found that resting and gravid females exhibited similar seasonal distributions in winter and spring, extending from Singer Island, FL to Cape Hatteras, NC. However, in summer and autumn resting females migrated farther north to Long Beach, NJ, whereas gravid females remained south of Cape Hatteras. The average migratory distance for resting females was 22% greater than for gravid females. The shorter migratory range of gravid females allows them to remain closer to the nursery grounds in Georgia and the Carolinas and devote more energy to their developing embryos. The distribution variability by sex and reproductive state may help to clarify some of the inconsistencies in the literature. |
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2. 13:45 An assessment of abundance and space use within a multi-species assemblage of sharks around a Georgia barrier island. Andrew Lyons*, Jacksonville University; Bryan Franks, Jacksonville University; Eric Reyier, Florida Atlantic Coast Telemetry Network; Bonnie Ahr, Florida Atlantic Coast Telemetry Network alyons3@jacksonville.edu
Understanding the reproductive habits of coastal sharks is important to develop effective management strategies. While considerable research has been conducted regarding shark nursery areas, there are still regions and species where detailed information is lacking, particularly regarding the presence, distribution, and habitat utilization of sharks between their primary and secondary nursery sites. To better understand the importance of Georgia barrier islands as nursery habitat, the shark community in the waters around Little St Simons Island was examined. This site is an isolated island with a network of tidal creeks, unaltered shoreline, and is located at the southern-most portion of the Altamaha River, the largest undammed river on the east coast of the United States. Preliminary sampling in 2018 suggested a region of potential parturition for multiple coastal shark species. In 2019 and 2020, a gillnet survey was completed within four habitat types around the island following a stratified random sampling design. Lemon (Negaprion brevirostris), finetooth (Carcharhinus isodon), blacktip (Carcharhinus limbatus), and bonnethead (Sphyrna tiburo) sharks were the most commonly caught species representing 96.5% of the catch data. Rates of recapture and supporting telemetry evidence demonstrated repeated use of areas serving as nursery sites. The presence of young-of-year (YOY) lemon sharks represents a potentially new primary nursery site for the species, one of the few identified pupping sites in US waters outside of Florida. The waterways surrounding Little St Simons offer ample protection with minimally disturbed adjacent shorelines that help to support this important summer nursery. |
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3. 14:00 Effects of Predator and Prey Distribution and Density on Habitat Use of an Intermediately Sized Marine Predator (mesopredator). Cheston Peterson*, FSU Coastal and Marine Laboratory; Ashley Dawdy, FSU Coastal and Marine Laboratory; Blake Hamilton, FSU Coastal and Marine Laboratory; Bryan Keller, FSU Coastal and Marine Laboratory; Chip Cotton, State University of New York at Cobleskill; Dean Grubbs, FSU Coastal and Marine Laboratory ctpeterson13@gmail.com
Passive acoustic telemetry and fishery-independent surveys were used to describe habitat use of bonnetheads (Sphyrna tiburo) and bull sharks (Carcharhinus leucas) in the Apalachicola Bay system and explore the relationships of predation risk and prey availability on marine mesopredator movement. Linear mixed models (LMM) were used to integrate telemetry data with blue crab (Calinectes sapidus) density data from fishery-independent otter trawl surveys conducted by FWC to explore the predator-prey dynamics of blue crabs, bonnetheads, and bull sharks. Bonnetheads and bull sharks were resident throughout the summer and exhibited site fidelity, and the proportion of the array used was positively correlated with body size in both species. Bonnetheads were not detected in habitats where blue crabs were most dense and the probability of bull shark presence was highest. Results of the LMM analyses suggested a significant negative relationship of bonnethead habitat use and bull shark presence probability, as well as a significant negative relationship in the interaction of bull shark presence and salinity (bull shark presence probability was highest at sites with the lowest average salinities). These results suggest habitat use in bonnetheads may follow predictions of optimal foraging theory and the ideal free distribution under the constraint of predation risk, which may be informative in understanding the roles of predation and prey availability in the habitat use of marine mesopredators such as small coastal sharks. |
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4. 14:15 Depredation Rates and Spatial Overlap of Great Hammerhead Sharks (Sphyrna mokarran) and Tarpon (Megalops atlanticus) in a Recreational Fishing Hotspot. Grace Casselberry*, University of Massachusetts Amherst; Gregory Skomal, Massachusetts Division of Marine Fisheries; Lucas Griffin, University of Massachusetts Amherst; Jacob Brownscombe, Carleton University; Alex Filous, University of Massachusetts Amherst; Joseph Dello Russo, University of Massachusetts Amherst; Jeff Kneebone, Anderson Cabot Research Center; Aaron Adams, Bonefish & Tarpon Trust; Steven Cooke, Carleton University; Andy Danylchuk, University of Massachusetts Amherst gcasselberry@umass.edu
Human activities, like recreational angling, are capable of altering the behavior of individual fish within populations and facilitate predation events, causing shifts in predator-prey dynamics and posing management challenges. The Atlantic tarpon (Megalops atlanticus) fishery in Florida is primarily catch-and-release, but fishing guides in the Florida Keys are increasingly reporting the loss of hooked tarpon to depredation, particularly by great hammerhead sharks (Sphyrna mokarran). Such interactions have the potential to impact both tarpon and hammerhead populations. Previous research of hammerhead and tarpon movements in the Florida Keys revealed that the Bahia Honda region of the Florida Keys is an area of significant spatiotemporal overlap between the two species. To better understand depredation in Bahia Honda, we used visual surveys to quantify depredation rates of tarpon by sharks, and acoustic telemetry to examine spatial overlap between predator and prey. Seventeen great hammerheads were tagged with acoustic transmitters and color-coded cattle tags to aid in visual identification of individuals, and 200 tarpon were implanted with acoustic transmitters. Results from standardized visual observations of fishing activity in spring 2019 indicate ~15% of hooked tarpon suffer depredation mortality by great hammerhead sharks, and that water current direction and angling intensity contribute to depredation susceptibility. Moreover, analyses of movement patterns of both species indicate that hammerheads modify their space use in Bahia Honda channel with increasing tarpon presence. Movement data coupled with the visual survey data, will be the foundation for solutions to reduce depredation events and decrease the potential for angler-shark conflict. |
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5. 14:30 Extinction Risk, Reconstructed Catches, and Management of Chondrichthyan Fishes in the Western Central Atlantic Ocean. B Talwar; Brooke, , María del Pilar Blanco-Parra, Alejandra Briones, Diego Cardeñosa, John Carlson, Patricia Charvet, Charles Cotton, Zoe Crysler, Danielle Derrick, Michael Heithaus, Katelyn Herman, Olga Koubrak, David Kulka, Peter Kyne, Oscar Lasso-Alcalá, Paol Anderson, Arizona State University; Christopher Avalos-Castillo, Universidad de San Carlos de Guatemela; Maria del Pilar Blanco-Parra, Consejo Nacional de Ciencia y Tecnología; Alejandra Briones, Dirección de Regulaciones Pesqueras y Ciencia; Diego Cardeñosa, Florida International University
; John Carlson, NOAA Fisheries Service Southeast Fisheries Science Center; Patricia Charvet, Universidade Federal do Ceará; Charles Cotton; Zoe Crysler, Simon Fraser University; Danielle Derrick, Department of Fisheries and Oceans, Resource Management and Sustainability, Marine Conservation Targets; Michael Heithaus, Florida International University; Katelyn Herman, Georgia Aquarium; Olga Koubrak, Dalhousie University; David Kulka, Department of Fisheries and Oceans; Peter Kyne; Oscar Lasso-Alcalá, Fundación La Salle de Ciencias Naturales; Paola Mejía-Falla, Wildlife Conservation Society- Colombia; Jorge Morales-Saldaña, Smithsonian Tropical Research Institute; Beatriz Naranjo-Elizondo, Universidad de Costa Rica; Andrés Navia, Fundación colombiana para la investigación y conservación de tiburones y rayas;
Nathan Pacoureau, Simon Fraser University; Juan Peréz-Jiménez, El Colegio de la Frontera Sur (ECOSUR); Riley talwar.brendan@gmail.com
Chondrichthyan fishes are among the most threatened vertebrates on the planet because many species have slow life histories that are outpaced by intense fishing. The Western Central Atlantic Ocean, which includes the greater Caribbean, is a hotspot of chondrichthyan biodiversity and abundance, but is historically characterized by extensive shark and ray fisheries and a lack of sufficient data for effective management and conservation. To inform future research and management decisions, we analyzed patterns in chondrichthyan extinction risk, reconstructed catches, and regulations in this region. We summarized the extinction risk of 180 sharks, rays, and chimaeras using contemporary IUCN Red List assessments and found that over one-third (35.6%) were assessed as Vulnerable, Endangered, or Critically Endangered largely due to fishing. Reconstructed catches from 1950 to 2016 reached their peak in 1992, then declined by 40.2% through the end of the series. The United States, Venezuela, and Mexico were responsible for most catches and hosted large proportions of the regional distributions of threatened species; these countries therefore held the greatest responsibility for chondrichthyan management. The abundance and resolution of fisheries landings data were poor in much of the region, and national-level regulations varied widely across jurisdictions. Regional collaboration as well as effective and enforceable management informed by more complete fisheries data, particularly from small-scale fisheries, are required to protect and recover threatened species and ensure sustainable fisheries. |