Session 10: AES Gruber IIRoom: Conference Theater2022-07-28 15:30 - 16:45 |
| Moderator: Jim Gelsleichter |
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1. 15:30 Multi-channel feeding by migratory sharks in a fluvial-dominated estuary – Implications for natural resource management. Blake Hamilton*, FSU; Oliver Shipley, UNM; Dean Grubbs, FSUCML blakerhamilton@gmail.com
Rivers can transport a substantial amount of allochthonous nutrients into coastal marine ecosystems. These nutrients are a significant contributor to estuarine productivity, resulting in increased fishery production. However, for migratory marine predators, the importance of nutrients from fluvial-dominated estuaries is unclear. We used carbon (? 13C) and sulfur (? 34S) stable isotope mixing models to identify the contribution of prey sources in fluvial-dominated estuarine habitat relative to nearby seagrass and offshore reef habitats to five shark species. We explored how the contribution of these sources varied as a function of shark length. Sharks generally exhibited a strong reliance on prey from fluvial-estuarine energy channels, with the youngest individuals displaying the highest reliance relative to larger individuals. Models suggested that sharks rely increasingly on nutrient sources from nearby seagrass or offshore reef habitats with age, potentially acting as vectors of nutrient transport across systems. These findings illustrate the importance of a fluvial-dominated estuarine system to migratory marine predators and suggest that these individuals may connect inshore and offshore food-webs. Estuarine systems with high fluvial-influence offer important nutrient subsidies for migratory species, which can transport that energy to adjacent, nutrient-limited systems. Changes to river-flow regimes could disrupt the channeling of fluvial nutrients to coastal marine systems, affecting migratory predator populations and their role in transporting these nutrients across the seascape. Managing water resources to encourage connectivity may buffer various aquatic systems from the effects of a changing climate while also maintaining healthy fisheries resources by protecting important coastal fish habitat. |
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2. 15:45 Linking Mercury Bioaccumulation and Feeding Ecology in Eight New York Bight Shark Species. Lisa Crawford*, Stony Brook University; Oliver Shipley, University of New Mexico; Jill Olin, Michigan Technical University; Anne McElroy, Stony Brook University; Michael Frisk, Stony Brook University lisa.crawford@stonybrook.edu
Sources and pathways of pollutant bioaccumulation in the marine food web can be assessed by combining measurements of chemical tracers with contaminant analysis. We evaluated resource partitioning using carbon (?13C) and nitrogen (?15N) stable isotopes and assessed the trophic transfer and spatial sources of total mercury (THg) in New York Bight (NYB) sharks. Muscle samples were harvested from 92 sharks (blacktip, N=3, blue, N=8, common thresher N= 14, dusky N=4, sand tiger N=12, sandbar N=39, shortfin mako N=8, white N=4) from New York Bight between 2018-2020 and analyzed for ?3C, ?15N, and THg. Median THg was highest in white sharks, followed by dusky, blue, shortfin mako, sandbar, blacktip, sand tiger, and common thresher. Though THg bioaccumulation is associated with trophic position, ?15N was only significantly correlated with THg in shortfin makos, likely due to the limited ranges of shark body sizes and life stages sampled. Blue sharks and shortfin makos occupied highly variable isotopic niches and tended to rely on offshore prey, compared to the other six species that tended to consume nearshore prey and occupied lower variance niches. Sharks occupying similar NYB habitats and trophic positions may have highly variable diets that lead to differential patterns of THg bioaccumulation. These results provide fundamental understanding of the feeding ecology and ecotoxicology of ecologically, recreationally, and commercially important New York Bight sharks, of which several are vulnerable or endangered. |
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3. 16:00 Organic Contaminants in Two Species of Thresher Sharks. Piper Rackley*, Georgia Institute of Technology; Aaron Carlisle, University of Delaware; Antonella Preti, Southwest Fisheries Science Center; Kady Lyons, Georgia Aquarium piperrackley@gmail.com
While Common Thresher Sharks (Alopias vulpinus) and Bigeye Thresher Sharks (Alopias superciliosus) are members of the same genus, they occupy spatially distinct habitats. Common Thresher Sharks are typically found in coastal waters over continental shelves. Bigeye Thresher Sharks tend to occupy deeper ocean regions in the mesopelagic zone. We aimed to test if known differences in these species’ ecological niches, specifically their proximity to areas of anthropogenic influence, would result in differences in their accumulation of persistent organic pollutants (POPs) and stable isotopes. Liver tissue from both species were obtained through fisheries-dependent and -independent methods and were extracted and analyzed for a suite of POPs. Mean polychlorinated biphenyl (PCBs), dichlorodiphenyltrichloroethane (DDT), and non-DDT-pesticide contaminants were higher in Common Thresher Sharks than Bigeyes. We were able to identify distinct differences in contaminant levels between the two species, which was in support of our hypothesis that there would be species-specific differences in the accumulation of POPs. This difference could be a result of the spatial proximity of Common Thresher Sharks to nearshore areas where anthropogenic activities (i.e. run-off, historic pollutant dumping, etc.) are more prevalent, increasing the potential that Common Thresher Sharks may be exposed to contaminants. The analysis of POPs present in each species of thresher sharks furthers our understanding of how each species segregates in the marine environment and implications for their anthropogenic exposure. |
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4. 16:15 Effects of Artificial Light at Night on Nurse and Blacktip Sharks. Abigail M Tinari*, Rosenstiel School of Marine and Atmospheric Science, University of Miami; Neil Hammerschlag, Rosenstiel School of Marine and Atmospheric Science, University of Miami; Austin Gallagher, Beneath the Waves; Steven J. Cooke , Fish Ecology and Conservation Physiology Laboratory, Department of Biology and Institute of Environmental and Interdisciplinary Science, Carleton University a.tinari@umiami.edu
Artificial light at night (ALAN) is a pervasive pollutant extending far from the original source, even into the water column in coastal waters. Previous studies have shown ALAN can suppress hormones, alter growth patterns, and cause tumors in teleost fishes. However, the effects of ALAN on elasmobranch physiology have yet to be investigated. To address this knowledge gap, we examined the potential effects of ALAN on melatonin levels in nurse and blacktip sharks sampled off Miami, Florida. We hypothesized that individuals occupying areas exposed to high ALAN would exhibit suppressed melatonin levels compared to conspecifics in adjacent areas with low ALAN. We further predicted species-specific differences in melatonin given known differences in mobility that would be expected to influence spatial exposure to ALAN (i.e., nurse sharks are highly resident versus blacktips which are highly mobile). Consistent with our predictions, nurse sharks sampled in high ALAN areas exhibited significantly lower melatonin levels compared to individuals sampled in low ALAN areas, whereas melatonin levels measured in blacktips did not differ between individuals sampled in areas exposed to high versus low ALAN. These results demonstrate, for the first time in sharks, that ALAN can suppress melatonin levels in wild sharks. Moreover, results suggest the effects of ALAN on shark physiology may be influenced by species-specific mobility; specifically, species that are highly resident to areas of high ALAN will be more prone to this anthropogenic pollutant compared to highly mobile species that readily move between areas of high and low ALAN. |