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    AES Behavior, Movements & Habitat Use II

    2021-07-22   10:45 - 12:15

    Moderator: Jeremy Vaudo

    1.  10:45  IN-PERSON    Region-specific movements of oceanic whitetip sharks in the western North Atlantic Ocean revealed by long-term satellite tracking. Jeremy Vaudo*, Guy Harvey Research Institute, Nova Southeastern University; Bradley Wetherbee, Guy Harvey Research Institute, Nova Southeastern University; Guy Harvey, Guy Harvey Research Institute, Nova Southeastern University; Mahmood Shivji, Guy Harvey Research Institute, Nova Southeastern University

    The oceanic whitetip shark (Carcharhinus longimanus) is a widely distributed species capable of long-distance travel, but relatively little is known about its long-term horizontal movements. We examined the seasonal movements and space use of oceanic whitetip sharks at two locations in the western North Atlantic using satellite telemetry. Twenty-three sharks (7 tagged off the Bahamas, 16 tagged off the Cayman Islands) were tracked for periods up to 929 d (Bahamas: 49–740 d; Cayman Islands: 314–929). Sharks displayed region-specific movements, with little distributional overlap between the Caribbean Sea and the outer western North Atlantic. Sharks tagged off the Bahamas showed a considerable individual variation in the timing of movements, but in general ranged over a larger area and made excursions as far north as Virginia, USA, during the summer and autumn. Movements of sharks tagged off the Cayman Islands were more restricted, with these sharks rarely leaving the northern Caribbean Sea. During these restricted movements, sharks in the Caribbean experienced little change in productivity and front index over time, but temperature fluctuated seasonally. Productivity and front index at the Bahamas tagging location were also relatively constant and similar to those experienced by sharks in the Caribbean, however, conditions to the north were more dynamic. During the summer, temperatures of the northern waters used by sharks tagged in the Bahamas approached those near the tagging site. The seasonally warming temperatures allow the sharks to expand their range northward where they experience stronger fronts, which may provide increased foraging opportunities.

    2.  11:00  VIRTUAL    Movement Patterns of the Tiger Shark, Galeocerdo cuvier, around Tahiti and Moorea, French Polynesia, South Pacific. Benjamin Marsaly*, University of Rennes 1; Eric Clua, PSL Research University: EPHE-CNRS-UPVD USR 3278 CRIOBE

    Even if French Polynesia is the world's biggest shark sanctuary, movements of the shark species distributed there remain poorly understood. Here we use acoustic telemetry to study the movement patterns of tiger sharks around the islands of Tahiti and Moorea, French Polynesia, during the 2014-2016 period. Acoustic transmitters were ingested or externally attached at the base of the shark's dorsal fins and provided acoustic data on 10 individuals during the study period. Preliminary analysis suggests seasonal and strong spatial variability in the use of the Tahitian coastal area. Two sites stand out by their high numbers of detection and their high level of residency: the “Vallée Blanche” site (NW of Tahiti) and the Papenoo outer reef (N of Tahiti). However, temporal patterns of activity at these two sites are different. If the regular practice of shark-feeding likely explains the presence of tiger sharks at the Vallée Blanche during the day, the intense activity at the Papenoo acoustic station suggests the presence of a natural aggregation site in this area. In addition to increasing our knowledge about their ecology, understanding tiger sharks movement patterns in French Polynesia is crucial to assess the effects of shark-feeding practices and the efficiency of the sanctuary implementation.

    3.  11:15  IN-PERSON    Preliminary insights into the movements of pregnant Porbeagles (Lamna nasus) in the Northwest Atlantic. Brooke Anderson*, School of Mathematical and Natural Sciences, Arizona State University; Neil Hammerschlag, Rosenstiel School of Marine and Atmospheric Science, University of Miami; Austin Gallagher, Beneath the Waves; Lisa Natanson, Northeast Fisheries Science Center, National Marine Fisheries Service; Heather Bowlby, Bedford Institute of Oceanography, Fisheries and Oceans Canada; James Sulikowski, School of Mathematic and Natural Sciences, Arizona State University

    The Northwest Atlantic Porbeagle (Lamna nasus) is overfished and effective management and recovery will depend on a comprehensive understanding of the population’s movements and habitat use. Knowledge of movements of pregnant females will be of particular conservation importance, yet such information is limited and often precluded by logistical constraints of determining reproductive status in live sharks. The current study confirmed pregnancy using a combination of the presence of fresh mating scars, ultrasonography, and plasma reproductive hormone concentrations (estradiol, progesterone, and/or testosterone), in four mature female Porbeagles captured off of Cape Cod, MA, USA, in late October 2020. These sharks were double-tagged with finmount satellite tags and year-long pop-off satellite archival tags (PSATs) to provide the first insight into three-dimensional movements and habitat preferences of confirmed pregnant Porbeagles throughout gestation. Based on preliminary analysis of movements for three individuals who provided adequate finmount satellite tag data, pregnant Porbeagles remained in continental shelf waters southeast of Cape Cod during early gestation and then moved off of the continental shelf in February 2021, when finmount tags ceased transmission for multiple months. Interestingly, two of these pregnant Porbeagles have returned to more northern waters on or near the continental shelf in late April and early May. Additionally, premature pop-off of one PSAT indicates pregnant Porbeagles may be swimming to maximum daily depths of up to over 1000 m. Pupping is expected to occur in late May or June, and information on movements and location around the time of pupping will be provided.

    4.  11:30  VIRTUAL    Migration and movement behavior of juvenile cownose rays (Rhinoptera bonasus) from Chesapeake Bay inferred from acoustic telemetry. Charles Bangley*, Dalhousie University; Ariana Baldwin, Smithsonian Environmental Research Center; Robert Fisher, Virginia Institute of Marine Science; Matthew Ogburn, Smithsonian Environmental Research Center

    The consistent use of nursery habitats is widespread among juvenile elasmobranchs, which are thought to constrain their movements to these nurseries in comparison to the more wide-ranging adults. However, nurseries with seasonally-changing conditions may require juveniles to undertake long-distance migrations for part of the year. The Chesapeake Bay functions as such a nursery for cownose rays (Rhinoptera bonasus) during the first summer and fall following birth. Adults migrate south along the U.S. east coast to overwintering grounds off Cape Canaveral, Florida before returning to nurseries in the spring. In order to determine whether juveniles undertake similar migrations, we tagged 32 young-of-year rays with acoustic transmitters and tracked them through collaborative receiver networks, which allowed us to observe their entire migratory range. We used hidden Markov modeling to identify areas where juveniles transitioned between migratory and non-migratory behavior and assessed seasonal site fidelity to non-migratory habitats. The migratory range of juvenile cownose rays was comparable to that of the adults, ranging from Port St. Lucie, Florida to Sandy Hook, New Jersey. Juvenile rays consistently showed non-migratory behavior in the vicinity of Cape Canaveral during winter and across a broad length of the U.S. Mid-Atlantic region during summer. The tagged rays showed evidence of site fidelity to their Florida overwintering habitat, but there was no evidence of site fidelity to summer habitats. While adults seem to show regional philopatry to the same nurseries during the summer, juveniles may range widely across different summer habitats until reaching maturity.

    5.  11:45  IN-PERSON    The Use of UAVs to Quantify Encounter Rates Between Humans and Juvenile White Sharks (Carcharodon carcharias) in Southern California. Patrick Rex*, California State University Long Beach; Dr. Chris Lowe, California State University Long Beach

    Southern California beaches serve as seasonal juvenile white shark (JWS) nursery habitats, and year-round human recreation areas. Anecdotal evidence of an increasing white shark population in the northeastern Pacific Ocean, along with rising popularity of beach-related recreation may increase human-JWS encounters. Developing an understanding of nearshore distributions, and quantification of human-JWS encounter rates may help manage beach safety concerns. Furthermore, determining if environmental conditions increase or decrease encounter rate may allow for predictions of times and locations that may be high risk for human-JWS encounters. Drone surveys are a cost-effective tool for gathering georeferenced census data for marine recreation groups (e.g. waders, surfers etc.) and JWS. High-resolution GPS and 4k resolution cameras on drones allow for geolocation of encounters and methods for observing shark behavior during encounters. From 2019 to present, over 1000 aerial surveys were flown, across 34 beach locations from San Diego to Santa Barbara. Environmental variables drawn from publicly available datasets (e.g. sea surface temperature, wave height etc), were used to look for patterns or trends in environmental conditions associated with human-JWS encounters. We show that of all classified recreational groups, surfers have the highest observed abundance, and have the highest rate of human-JWS encounters. Encounters appear spatially restricted to 5 distinct beaches, where large aggregations of JWS are present. Human-JWS encounter rates were further observed to correlate with specific environmental variables associated with peak ocean recreationalist numbers. This indicates the probability of human-JWS encounters is driven by human behavioral patterns, rather than JWS behavioral patterns.

    6.  12:00  IN-PERSON    Age, Growth, and Maturity of the Bonnethead, Sphyrna tiburo, in the Gulf of Mexico. Bryan Frazier*, SCDNR; Elizabeth Vinyard, SCDNR; Douglas Adams, FL-FWC; Dana Bethea, NOAA Fisheries; William Driggers III, NMFS; Marcus Drymon, MSU; Andrew Fields, TAMU-CC; Dean Grubbs, FSU; Jill Hendon, USM; Eric Hoffmayer, NMFS

    The bonnethead (Sphyrna tiburo) occurs in the western Atlantic Ocean from North Carolina to southern Brazil, including the Gulf of Mexico. The bonnethead is placentally viviparous and unique among coastal sharks in the region, as its gestation period lasts for only five months and parturition occurs in the late summer/early fall. Published estimates of growth suggest large differences in life histories between the waters off the southeastern US coast (Atlantic) and eastern Gulf of Mexico (GOM), with no life history estimates generated for the western GOM. The objectives of this study are to (i) generate population-specific growth estimates for the eastern and western GOM, (ii) compare growth within and between populations in the GOM and Atlantic, and (iii) investigate whether clinal variation in growth exists in the eastern and western GOM. Estimated age and length data will be used to generate population-specific growth and maturity models. Models will be compared to previously published growth models in the Atlantic and GOM to examine differences in growth among and between regions.

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