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    AES Gruber II

    2021-07-21   10:45 - 11:45

    Moderator: Bryan Frazier

    1.  10:45  IN-PERSON    CANCELLED - Potential Exposure of Young Bull Sharks to Multiple Algal Toxins in an Important Florida Nursery. Michelle Edwards*, Harbor Branch Oceanographic Institute, Florida Atlantic University; Michael McCallister, Harbor Branch Oceanographic Institute, Florida Atlantic University; Charles Bangley, Smithsonian Environmental Research Center; Matthew Ogburn, Smithsonian Environmental Research Center; Adam Schaefer, Harbor Branch Oceanographic Institute, Florida Atlantic University; Matthew Ajemian, Harbor Branch Oceanographic Institute, Florida Atlantic University

    2.  11:00  VIRTUAL    Growth, Habitat Use and Movement Patterns As Drivers of Mercury and Methylmercury Tissue Concentrations of Bull Sharks. Laura Garcia Barcia*, Florida International University; Gina Clementi, Florida International University; Kirk Gastrich, Florida International University; Valerie Hagan, Mote Marine Lab; Jack Morris, Mote Marine Lab; Heather Moncrief-Cox, NOAA Fisheries SEFSC; Yaniela Lorenzo, Florida International University; Bradley Strickland, Virginia Institute of Marine Science; Philip Matich, Texas A&M; Demian Chapman, Mote Marine Lab

    Mercury in surface ocean waters has nearly tripled in the last century. This pollutant biomagnifies through the food web mostly in the form of methyl-mercury, a potent neurotoxicant. Methyl-mercury can have detrimental effects on wildlife health including visual impairment, inhibited growth, lethargy, and lower reproductive success.Sharks are considered slow-growing species with low fecundity and late maturation. When paired with their upper-level trophic position, these characteristics allow for them to accumulate elevated concentrations of mercury and methyl-mercury. Estuarine and coastal species such as the bull shark (Carcharhinus leucas) are species of concern in terms of toxicant exposure since they exploit estuarine areas that are directly adjacent to contaminant runoffs entering marine environments. This study aims to determine which stages in the life of coastal sharks are more vulnerable to mercury accumulation and its potential negative effects. To do so, we assessed the total mercury, methyl-mercury and selenium levels of 140 bull sharks of different life stages throughout the Gulf of Mexico and Atlantic coast of Florida. Concomitantly, we implanted acoustic tags on a subset of juvenile sharks which, combined with stable isotope data, provide novel insights into the behavioral and dietary decisions that have a significant effect on mercury exposure at a young age. In light of worldwide population declines in apex predators, understanding the ecological factors that regulate exposure of contaminants is vital due to lethal and sub-lethal effects of pollution.

    3.  11:15  VIRTUAL    Habitat use of the daggernose shark Isogomphodon oxyrhynchus (Müller & Henle, 1839) based on microchemistry analysis. Leonardo Feitosa*, Bren School of Environmental Science and Management, University of California; Rosangela Paula Lessa, Laboratório de Dinâmica de Populações Marinhas (DIMAR), Universidade Federal Rural de Pernambuco

    Habitat use information is crucial for discovering key areas for population maintenance and effective conservation efforts. While most of habitat use research with elasmobranchs has focused on telemetry methods, vertebrae microchemistry has demonstrated to be an important technique, especially considering that we can access individual lifelong data. Here, we report habitat use patterns of the daggernose shark, Isogomphodon oxyrhynchus, one of the most endangered shark species in the world, from 19 samples collected in the Brazilian Amazon coast (BAC) in two periods: in the 1990s and 2010s. Vertebrae were analyzed in a laser ablation inductively coupled mass spectrometry (LA-ICP-MS) for 24Mg, 55Mn, 86Sr, 138Ba and 43Ca for element:Ca ratios. We used one-way PERMANOVAs on multi and single-element settings comparing life stages, sexes, and decades of sample collection. We obtained significant differences (p < 0.05) for sexes for multi-elements and Sr:Ca ratios. Moreover, life stages differed for Mg:Ca and Mn:Ca ratios, and decades differed for multi-element and Ba:Ca ratios. Furthermore, an NMDS analysis based on all elements investigated demonstrated little overlap between samples from different decades regardless of life stage and sex. Nevertheless, the results obtained highlight that individuals tend to have little variation in habitat use across life stages, which means that they likely fulfill their whole life cycle in the same area. Therefore, the BAC should be considered critical habitat for this species, especially given its small geographic range that goes from Trinidad & Tobago to the eastern BAC.

    4.  11:30  VIRTUAL    Using Integral Projection Models to Estimate Population Growth Rates in Elasmobranchs. Brian Moe*, Florida State University; Charles Cotton, SUNY Cobleskill; Dean Grubbs, Florida State University Coastal and Marine Lab

    Traditionally, estimates of population growth derived from life-history parameters come in the form of discrete models like the Leslie Matrix, categorizing individuals based on age classes, or the Euler-Lotka model, typically presented as a generalization across the entire lifespan. While these methods estimate population growth quite well, they fall short of depicting the population from an accurate biological perspective. Elasmobranchs do not grow in discrete time, but rather, continuously. Maturity does not occur at abrupt, discrete moments in life, but instead as a fluid transition taking place over a range of sizes and ages. As such, using discrete models to describe the growth of populations with continuous traits fails to capture the true nature of their biology. Integral projection models (IPMs) describe traits using probability density functions and regression models. Thus, these models depict population growth and life-history as smooth continuous processes, which is far more applicable for elasmobranchs than discrete models. The use of IPMs is commonly applied in plant studies in which growth and reproduction does not occur in discreet stages. However, this approach is rare among studies of vertebrates, save a few recent studies. Here, we propose an IPM based on both age and size related aspects of life-history to model elasmobranch population growth. While IPM generated mean parameter estimates are not very different from those generated by traditional discrete models, the margin of deviation around IPM estimates is far smaller than their discrete counterparts. More importantly, IPMs describe growth from a far more biologically intuitive framework.

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