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    V: SSAR Seibert Award I

    2021-07-21   11:00 - 11:45

    Moderator: Rulon Clark

    1.  11:00  VIRTUAL    Developing Alternative Control Strategies for Invasive American Bullfrogs to Protect Threatened Giant Gartersnakes and Their Native Anuran Prey. Richard Kim*, University of California, Davis

    Conservation interventions, such as invasive species removal, must proceed carefully to avoid unanticipated consequences. While culling invasive predators like American bullfrogs (Lithobates catesbeianus) could benefit some native herpetofauna, it could deplete juvenile and larval bullfrogs that threatened giant gartersnakes (Thamnophis gigas) rely on as prey. If adult bullfrogs cannibalize young, insufficient removal of adults could result in an overcompensatory increase of juveniles. Thus, accounting for important biotic drivers like trophic interactions can facilitate the recovery of native prey, like sierran treefrogs (Hyliola sierra), and giant gartersnakes. To quantify how predator-prey interactions influence the efficacy of culling strategies, we developed a continuous-time model of stage-structured reciprocal intraguild predation with alternative prey. We explored the recovery trajectory of gartersnakes and treefrogs after culling each stage or both stages of bullfrogs at different rates and how competition for treefrogs and bullfrogs’ cannibalism affect the recovery trajectories. We found that adult-specific culling can yield the fastest recovery for both gartersnakes and treefrogs. However, when bullfrogs display high cannibalism, 1) insufficient culling of the adults can result a transient overcompensation of juvenile bullfrogs and 2) both-stage culling can result a shorter transient period until native-species equilibrium, with the caveat that transient overcompensation of juvenile bullfrogs is possible. Although culling bullfrogs can promote the recovery of both gartersnakes and treefrogs, nuanced strategies based on system-specific predator-prey interactions can increase its efficacy and reduce the risk of unintended consequences.

    2.  11:15  VIRTUAL    Gillnet Illumination as an Effective Measure to Reduce Sea Turtle Bycatch. Phil Allman, Florida Gulf Coast University; Andrews Agyekumhene, University of Ghana; Leyna Stemle*, University of Ghana

    The growing demand for fish around the world is an immediate threat to marine megafauna that are unintentionally captured in fishery operations. Bycatch mitigation strategies have successfully reduced this risk. We explored the effectiveness of gillnet illumination to reduce sea turtle captures in 2 artisanal fisheries in Ghana, under normal fishing conditions. We quantified catch of targeted species and turtle bycatch from 20 boats for 15 months. For 10 of these boats, we placed green LED lights at each 10-m interval on the net. We also quantified target catch and turtle bycatch from 30 boats for 8 months. In 15 of these boats, green LED lights were installed at 15-m intervals. Both lights exhibited an 81% decrease in turtle captures (W = 1, p <0.001, n = 20; W = 215, p <0.001, n = 30) compared with control boats. Illuminated nets resulted in fewer turtle catches for leatherback (Dermochelys coriacea), olive ridley (Lepidochelys olivacea), and green turtles (Chelonia mydas) (p <0.05 for all species). Target catch (mass) (W = 53, p= 0.853 n = 20; W = 76, p= 0.449, n = 23) and value (W = 50, p= 1, n = 20; W = 69, p= 0.728, = 23) were not different across treatments. Our study affirms net illumination can reduce capture rates of 3 species of sea turtles, including the imperiled leatherback. Gear modification methods can successfully reduce bycatch and have broad applications for multiple species in different fisheries.

    3.  11:30  VIRTUAL    The tadpole or the fungus: How host and pathogen condition drive infection dynamics. Spencer Siddons*, Purdue University; Catherine Searle, Purdue University

    Environmental stressors can influence host and pathogen condition in ways that impact their susceptibility and infectivity, ultimately driving disease outcomes. Studies commonly focus on host condition as the driving factor in disease outcomes, with little focus on the pathogen condition which is exposed to the same stressor as the host. Therefore, we influenced the condition of the pathogenic fungus Batrachochytrium dendrobatidis (Bd), and tadpole hosts (Lithobates clamitans) prior to combing them, to better understand whether the host condition or pathogen condition is driving infection patterns. We separately exposed Bd and tadpoles to NaCl, or a commercially available road salt at one of two concentrations for two weeks and measured growth and survival factors. We then combined the Bd with tadpoles for three weeks, and measured infection outcomes via qPCR. We found that Bd zoospore densities were reduced in both salt types and concentrations compared to controls, but found no differences between salt types. Throughout the entire experiment, tadpole mortality was higher when tadpoles were exposed to the road salt. Further, lower infection prevalence was found to be driven by treatments where tadpoles were exposed to salt and Bd was unexposed to salt. This is counter to other studies that propose environmental stressors increases infection risk, and suggests tadpoles predisposed to poor conditions brought on by environmental stressors may cause them to be low competent hosts. Our study highlights the importance of incorporating host and pathogen condition when investigating impacts of environmental stressors.

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