Session 46: AES Environmental Contaminants (first 2)/ Ecology (last 6)Room: Conference Theater2022-07-31 10:00 - 12:00 |
| Moderator: Bryan Frazier |
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1. 10:00 What do plasma mercury levels tell us about mercury exposure and uptake in sharks and rays? James Gelsleichter*, University of North Florida jim.gelsleichter@unf.edu
Because of its tendency to accumulate in upper trophic-level predators and potential toxicity, the non-essential metal mercury (Hg) poses significant threats to elasmobranch populations as well as humans that consume products from these fishes. Due to this, there have been many studies on Hg accumulation in elasmobranchs, most of which have focused on levels in edible tissues (i.e., muscle, fin) and/or internal targets of xenobiotic metabolism and/or toxicity (e.g., liver, kidney, brain). However, recent studies have reported on Hg levels in elasmobranch plasma; a sample matrix that may hold special value because of the largely non-invasive nature by which it can be collected, but also one that may be limited in its use by low accumulation of Hg. Therefore, this study examined the effectiveness of using plasma Hg levels as an indicator of Hg exposure and internal Hg burden in elasmobranchs. To accomplish this, we measured and compared Hg concentrations in plasma and muscle from a variety of coastal shark species to determine if plasma Hg levels could be used to predict internal Hg burden. We also explored the range of plasma Hg concentrations in ~25 shark and ray species from a range of habitats. We argue that plasma Hg levels may only be suitable for predicting internal Hg burden in a limited number of “high exposure” species. We explored ways to improve on the value of this approach, as it may have use for differentiating between environmental Hg exposure and long-term patterns of Hg accumulation. |
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2. 10:15 The Quantification of Young-of-the-Year Shark Microplastic Ingestion in South Carolina Estuaries. Morgan Lattomus*, College of Charleston; Bryan Frazier, South Carolina Department of Natural Resources; Ashley Galloway, South Carolina Department of Natural Resources; Gorka Sancho, College of Charleston; Barbara Beckingham, College of Charleston lattomusme@g.cofc.edu
Coastal cities around the world have been recorded with elevated microplastic pollution concentrations in their respective waterways. South Carolina urban estuaries are no exception, with documented elevated concentrations of consumed microplastics in planktivorous filter feeding fishes such as the Atlantic Menhaden (Brevoortia tyrannus). While there has been some work internationally documenting microplastic ingestion in sharks, very little is known about adult sharks in South Carolina estuaries and even less is known regarding young-of-the-years. South Carolinian estuaries are important birthing grounds for several species of Atlantic sharks, yet there is insufficient information how South Carolina’s urbanized coastal centers affect these vital estuarine ecosystems. In this study, microplastic ingestion is documented for the first time in Atlantic blacktip (Carcharhinus limbatus), finetooth (Carcharhinus isodon), scalloped hammerhead (Sphryna lewini) and carolina hammerhead (Sphryna gilberti) sharks, and for the first time in Atlantic sharpnose (Rhizoprionodon terraenovae) young-of-the-years. The most abundant microplastics ingested were fibers, which is reflective of recorded environmental abundance obtained through sediment and water samples. The highest amounts of microplastic were found in sharks with diets of mainly planktivorous fishes, averaging 0.01111 ± 0.00412 microplastics per gram of fresh weight (MPs/g FW) per shark, with the average across all species being 0.00504 ± 0.00091 MPs/g FW per shark. These results are similar to the concentrations found in adult sharks, suggesting that juveniles ingest similar quantities to mature sharks within the first several weeks of their lives. |
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3. 10:30 Multi-year provisioning reduces the local space use of a marine apex predator. Vital Heim*, Department of Environmental Sciences, Zoology, University of Basel; Maurits P. M. van Zinnicq Bergmann, Institute of Environment, Department of Biological Sciences, Florida International University; Matthew J. Smukall, College of Fisheries and Ocean Science, University of Alaska Fairbanks; Tristan L. Guttridge, Saving the Blue vital.heim@gmail.com
Wildlife tourism provisioning is a rapidly growing global industry that has the potential to alter target species behavior and movement, which has consequences for individual fitness and ecosystem dynamics. While short-term impacts on the target species are relatively well described, long-term effects have received considerably less attention. Here, we used passive acoustic telemetry with dynamic Brownian bridge movement models (dBBMMs) to investigate multi-year changes in movement between provisioned and naïve great hammerhead sharks, Sphyrna mokarran, at a known provisioning site in Bimini, The Bahamas, where shark-feeding has been conducted since 2012. Dynamic BBMMs revealed clear differences between provisioned and naïve sharks with provisioned sharks having a smaller space use than naïve sharks. Further, the space use of provisioned sharks became increasingly focused towards the dive site over time and provisioned sharks displayed a high degree of overlap in their core activity spaces compared to naïve sharks. Naïve sharks showed stable space use patterns over time that differed spatially from the patterns observed in provisioned sharks. Our results may serve as a foundation for better understanding downstream fitness costs for individuals and potentially broader ecosystem effects resulting from wildlife tourism provisioning. Our findings also demonstrate the potential of combining individual-based behavioral observations with multi-year movement data sets to investigate long-term effects of wildlife tourism provisioning on the movement behavior of target species. |
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4. 10:45 Maternal Provisioning and Isotopic Influence on Young-of-Year Hammerheads Along the Southeast US Coast. Ashley Galloway*, South Carolina Department of Natural Resources; Kady Lyons, Georgia Aquarium; Douglas Adams, Florida Fish and Wildlife Conservation Commission; Eric Reyier, Kennedy Space Center Ecological Program; Christine Bedore, Georgia Southern University; Jim Gelsleichter, University of North Florida; Amanda Barker, Texas A&M Corpus Christi; David Portnoy, Texas A&M Corpus Christi; Bryan Frazier, South Carolina Department of Natural Resources gallowaya@dnr.sc.gov
Scalloped (Sphyrna lewini) and Carolina Hammerheads (S. gilberti) are sympatric cryptic species, and neonates and young-of-year (YOY) of both species use overlapping coastal and estuarine nursery areas along the US southeast coast. Condition metrics and stable isotope signatures from multiple tissues were investigated to explore maternal investment and trophic differences between species after genetic confirmation of identity. Muscle tissue was used as a proxy for maternal isotopic signatures while fast turnover tissues better reflected the YOY resource use. Hepatosomatic index and liver lipid content metrics indicate that neonate Scalloped and Carolina Hammerheads rely heavily on prenatal maternal provisioning during their first weeks of life, presumably to support them energetically until exogenous feeding begins. Evidence of maternal investment was also reflected in neonatal isotopic tissue signatures which differed by species and were more variable in YOYs depending on tissue type and turnover rate. While these two hammerhead species are sympatric, multiple metrics suggest differences in maternal resource use and individual embryonic provisioning that may reveal differences in ecology. |
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5. 11:00 The diet of tiger sharks on Norfolk Island inferred from biochemical markers. Lauren Meyer*, Flinders University; Lisa Hoopes, Georgia Aquarium; Charlie Huveneers, Flinders University lauren.meyer@flinders.edu.au
Norfolk Island is a small island in the Pacific Ocean, ~1,400 km east of Australia that supports a broad diversity of temperate and tropical marine life, including many shark and pelagic fish species. In particular, Norfolk Island is home to a large aggregation of mature female tiger sharks Galeocerdo cuvier, with unknown diet, foraging ecology, and movement patterns. While the reliability of this aggregation makes Norfolk Island an ideal site to uncover the ecology of these top predators, no work to date has quantitatively explored what tiger sharks consume in this region, or how long they spend in these coastal waters. The local community has also raised concerns about the disposal of cow offal, rubbish, and fish frames, which are presumed to attract the tiger sharks that are observed feeding at the disposal sight. Here, we used stable isotopes and fatty acids from 60 tiger shark blood and muscle samples collected in 2020 and 2021 to quantify the role of cow offal in the diet of these generalist predators. Despite the frequent observation of tiger sharks consuming cow offal, isotope models suggest that local seabirds are the predominate prey source for these large tiger sharks sampled around Norfolk Island. |
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6. 11:15 Environmental Influences on Planktivorous Elasmobranchs at Cocos Island, Costa Rica. Julia Saltzman*, University of New Hampshire; Easton White, University of New Hampshire juliasaltzman21@gmail.com
Many species of charismatic marine megafauna are globally threatened. Planktivorous elasmobranchs are no exception to this. A key life history trait of planktivorous elasmobranchs is their seasonal aggregations in tropical environments. These aggregations make it difficult to separate population trends from fluctuations. In order to make this separation, we use data obtained over the last 30 years by a small group of divers at Cocos Island, Costa Rica, one of the oldest marine reserves in the world. We expand past work at Cocos by focusing on planktivorous elasmobranchs, to determine whether the observed fluctuations in elasmobranch sightings correspond with environmental variability or if they can be used to better understand long-term population trends. White et al. 2015 found that at Cocos, the odds of occurrence for whale sharks has increased by 4.5% each year and peaks in whale shark presence occurred every 3 years. However, the reasons for this remain unknown. Is this because of environmental conditions and food availability? In other locations, aggregations, abundance, behavior, and movement of planktivorous elasmobranchs is based on predictable food-pulses of zooplankton. In this study, we employ a set of quantitative approaches to determine if this is the case at Cocos. Specifically, we use a set of generalized linear mixed models to analyze over 30,000 records of frequency of occurrence for three planktivorous elasmobranchs (whale sharks, manta rays, and mobula spp.) We found that, in general, for planktivorous elasmobranchs, environmental conditions have clear influences on their occurrence and relative abundances. |
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7. 11:30 The Effect of Temperature and Association with Benthic Structure on White Shark Movements in the WNA using Acoustic Telemetry. Jackson Hooten*, Jacksonville University; Bryan Franks, Jacksonville University; Robert Hueter, OCEARCH; Chris Fischer, OCEARCH; Nigel Hussey, University of Windsor jax@environmentservices.com
The white shark (Carcharodon carcharias) is an apex predator with a wide-ranging distribution in temperate and tropical waters. While there is amassing knowledge regarding white shark movements and migration, population dynamics, foraging ecology, and reproductive biology throughout its global range; the white shark population in the western North Atlantic (WNA) is generally understudied particularly regarding the drivers of seasonal movements and habitat use. To that end, we first used automated acoustic telemetry to: 1) refine seasonal residency and migration patterns using long-term transmitters. We then examine: 2) coarse and fine-scale space use within and between residency areas in response to water temperature, and 3) determine if sharks disproportionately associate with structure when in winter residency areas to potentially exploit richer foraging areas in the region. From 2016-2021, forty-one white sharks were tracked in the WNA for up to four years. Acoustic telemetry data reinforced previous results, including satellite derived data, demonstrating that white sharks in the WNA exhibit strong regional fidelity and seasonal residency with distinct periods of migratory movements. The variability in large-scale shark movements was at least partially driven by water temperature over temporal scales. While there was evidence of association with submerged structures, the pattern was unclear. These findings add to existing knowledge on the species particularly by furthering understanding of the drivers of movement patterns and space use of the WNA population. A thorough knowledge of the space use, particularly habitat preferences and drivers of movement, provides critical information to manage this species in the region. |
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8. 11:45 Does the Oxygen Minimum Zone Constrain Shortfin Mako Shark Distribution in the Eastern North Pacific? Michael Byrne*, University of Missouri; Jeremy Vaudo, Nova Southeastern University; Heidi Dewar, NOAA, Southwest Fisheries Science Center; Bradley Wetherbee, University of Rhode Island; Mahmood Shivji, Nova Southeastern University byrneme@missouri.edu
For fishes, temperature and dissolved oxygen concentration can play an important role in determining species distributions. Oxygen minimum zones (OMZ) form in eastern tropical regions of the world’s oceans and are characterized by high stratification as narrow warm surface layers sit atop cold hypoxic waters. The shoaling of cold hypoxic waters in OMZs may effect the movements of pelagic sharks with high oxygen consumption requirements. To test this, we compared the distributions of shortfin mako sharks (Isurus oxyrinchus) tracked via satellite telemetry in the western north Atlantic (WNA, n = 27), where dissolved O2 is unlikely a limiting factor, and the eastern north Pacific (ENP, n = 87) ocean, with an extensive OMZ. Makos in the WNA consistently inhabited tropical regions with warmer sea surface temperature (SST) than those used by makos in the ENP. Dissolved O2 concentrations in areas used by mako sharks in the ENP decreased rapidly at SST > 25o C, which was not observed in the WNA. This suggests the tropical distribution of makos in the ENP is limited by a combination of warm temperature and low O2 concentrations at depth. The southern pelagic distribution of makos in the ENP corresponds to the boundary of the North Equatorial Current (NEC), which acts as a conduit extending the OMZ westward into the Pacific, and thus the NEC may function as a soft ecology boundary. These results have implications for the potential effects of climate change which are expected to increase the extent of OMZs. |