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    P1: AES posters

    2021-07-26   16:00 - 18:00

    To view the posters go to You will be able to chat one-on-one during the Monday poster session, the e-poster platform.

    1.  16:00  Mechanical Properties of Shark Skin. Madeleine Hagood*, Florida Atlantic University; Marianne Porter, Florida Atlantic University

    Shark skin may act as an exotendon altering swimming performance. Shark skin is composed of dermal denticles embedded in the stratum compactum, where an elastic network is formed between denticles and collagen fibers. This network stretches in two distinct orientations of uniaxial stress (longitudinal and hoop, or circumferential), transmitting forces during swimming, and the denticles and collagen fiber networks impact shark skin mechanics. Here, we quantify the anisotropic mechanical properties of shark skin and the impacts of the collagen fiber network and dermal denticle density among five shark species (N=14). Skin was dissected along the body as a grid of 5x5cm squares. We quantified the denticle density and collagen fiber angles for each skin square with ImageJ using stereoscopic microscopy. Four skin pieces, two per orientation (longitudinal and hoop), were dissected from each grid square, and tested in tension until failure at a 2 mm/s strain rate on an Instron E1000. We generated stress-strain curves for each tensile test and calculated mechanical properties: ultimate strength (MPa; maximum tensile stress), toughness (MPa; ability to absorb energy until failure), and Young’s Modulus (MPa; ability to resist tension). For each mechanical property, we found significant differences among species, and skin was stronger and stiffer in the hoop compared to longitudinal orientation. We did not find an effect of testing orientation on toughness; however, as dermal denticle density increases, skin toughness decreases. These data show differences in mechanical properties between testing orientations, providing support for the exotendon hypothesis of shark skin.

    2.  16:00  Are Bull Sharks from Florida Rivers Exposed to Harmful Levels of the "Forever Chemicals?" James Gelsleichter*, University of North Florida

    Per- and polyfluorinated alkyl substances (PFAS) are a large family of human-produced chemicals used in a variety of commercial products such as stain-resistant fabrics, non-stick cookware, and fire-fighting foams because of their water- and oil-repelling properties and high heat resistance. There has been growing concern about the occurrence of PFAS in the environment because of their high stability, a feature that has led many to refer to them as the “forever chemicals.” There is special concern about PFAS accumulation in top marine predators; however, very few studies have examined PFAS uptake in sharks despite their tendency to accumulate higher levels of environmental pollutants than most other fish. We examined concentrations of 24 PFAS in plasma of juvenile bull sharks from the Caloosahatchee River, a wastewater-impacted estuary in southwest Florida that represents a critical habitat for this species. We detected only 1 PFAS consistently in bull shark plasma; the chemical perfluorooctanesulfonic acid (PFOS), which was once used extensively in stain repellents and other products until its primary U.S. manufacturer voluntarily phased out its production beginning in 2002 due to concerns about its widespread occurrence in the environment. Plasma PFOS concentrations were low in juvenile bull sharks compared to other FL wildlife that have been tested, suggesting minimal potential for toxic effects in this population. Additional work will be conducted on juvenile and adult bull sharks from other Florida sites to compare PFAS contamination levels and explore the possibility that larger individuals are exposed to greater, potentially toxic levels due to bioaccumulation.

    5.  16:00  Validating the Use of Tethered Accelerometry Data Loggers to Study White Shark Predatory Behavior in the Western North Atlantic. Samantha McPherson*, University of New England; Megan Winton, Atlantic White Shark Conservancy; Kathryn Ono, University of New England; John Mohan, University of New England; James Sulikowski, Arizona State University; Gregory Skomal, Massachusetts Division of Marine Fisheries

    Accelerometry data loggers (ADLs) placed on white sharks can provide insight into their predatory behavior and energetic requirements during the seasonal feeding aggregation at Cape Cod, Massachusetts. In sharks, ADL packages are typically secured to the dorsal fin, but a towed ADL tethered to an intramuscular dart has been developed for attachment with minimal stress to the animal. These data may include noise attributable to independent tag motion, and accuracy of motion and body posture data collected by the tag has not been systematically assessed. This study compares ADL-derived estimates of tailbeat frequency (TBF) to video observations of swimming behavior collected by the tag to validate use of tethered ADLs for studying shark behavior. We deployed tethered ADLs (CatsCam, CATS, Germany) on 14 free-swimming white sharks off the coast of Cape Cod during June-November, 2019 and 2020. Data collected by triaxial accelerometers and gyroscopes were processed using continuous wavelet transformation and spectral analysis to extract TBF. For a subset of sharks, CatsCam footage was annotated to visually estimate TBF throughout the duration of the videoed track for comparison, to determine whether data from tethered ADLs accurately reflects the shark’s observed swimming behavior. Resulting estimates of TBF will be used to model metabolic rate and daily energy expenditure of individual white sharks; combining this information with available data on energy content of gray seal tissue will allow us to estimate white sharks’ daily feeding requirements, toward an understanding of their role in modulating seal populations during the Cape Cod aggregation.

    7.  16:00  Metal heads: Physiological and neurological effects of methylmercury on a small coastal elasmobranch, Mustelus canis. Maria Auxiliadora Sabando Plaza*, University of Delaware; Mi-Ling Li, University of Delaware; Aaron Carlisle, University of Delaware

    As mid to upper trophic level predators, elasmobranchs are well known to have elevated levels of mercury and its more toxic, organic form methylmercury (MeHg). However, the sublethal effects of exposure to MeHg, which are known to impact animal behavior, cognitive ability, and physiology, remains largely undescribed. In this study, we establish baseline information on how thephysiology ofa small, demersal, elasmobranch species (Mustelis canis, smooth dogfish)is impacted by chronic, sublethal exposure of this widespread and potent contaminant. We assess sublethal effects of different levels of exposure using different physiological parameters including aerobic scope measured via oxygen consumption and swimming speed, growth rate, and food consumption.As a secondary objective we will use a novel approach where we assess cognitive impacts by measuring learning ability and memory through operant conditioning. The lethality of methyl mercury across different taxa has been well researched, and its sublethal effects have only primarily been investigated in relationship to human health with little focus on fish that carry substantial mercury burdens. Contaminants may impact fundamental behaviors such as foraging, prey capture, swimming behavior, memory, and learning, traits which are critical to the survival of elasmobranchs. Filling this current knowledge gap through assessing effects on physiology and behavior following sublethal exposure to contaminants can give us an idea of how the fitness of elasmobranchs, which play important roles in marine ecosystems, may change in an ocean increasingly challenged by anthropogenic contaminants.

    4.  16:00  The Effect of Terminal Gear Modifications on the Total Mortality of the Shortfin Mako, Isurus oxyrinchus. Bryan Keller*, NOAA Fisheries - Office of International Affairs and Seafood Inspection; James Reinhardt, NOAA Fisheries - Office of Habitat Conservation - Restoration Center; Yonat Swimmer, NOAA Fisheries - Pacific Islands Fisheries Science Center; Craig Brown, NOAA Fisheries - Southeast Fisheries Science Center

    The shortfin mako, Isurus oxyrinchus,is a highly mobile, pelagic species globally distributed throughout tropical and temperate seas. Due to its conservative life history, this species is vulnerable to population depletion, with the North Atlantic shortfin mako stock being overfished and undergoing overfishing. TheInternational Commission for the Conservation of Atlantic Tunas (ICCAT) has therefore identified the need to better understand the effect of terminal gear modification as a bycatch mitigation measure in longline fisheries. Here we update two meta-analyses as one of the referenced studies was found to have a confounding variable that resulted in interpreting a bait effect as a hook effect. In both cases, significant differences in catchability are lost between hook types. For at-haulback mortality, the cited sources from the two meta-analyses were combined to maximize sample size; an updated model demonstrates a significant reduction of 10% in at-haulback mortality due to circle hook use. In review of additional publications, shortfin mako caught with circle hooks vs. J-hooks were twice as likely to be mouth hooked vs. foul or gut hooked, with the latter two being at least 4.5 times more lethal than mouth hooking. Overall, our paper demonstrates circle hook use is effective for reducing total mortality of the species and improves the probability of survival of shortfin mako incidentally captured in longlining fishing operations.

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