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    AES Ecology

    2021-07-23   09:15 - 10:15

    Moderator: James Anderson

    1.  09:15  VIRTUAL    Community and Trophic Ecology of Elasmobranchs and Large Teleost Fishes in the Apalachicola Bay System, Florida. Blake Hamilton*, FSUCML

    Coastal ecosystems, especially estuaries, are highly productive systems that often provide essential habitat for many marine species while also experiencing elevated anthropogenic stress due to their proximity to human activity. These stressors can be direct (e.g. overexploitation of fisheries resources) or indirect (e.g. upstream water diversions for human consumption or agriculture) and have the capability of altering ecosystem functioning and trophic dynamics, the understanding of which are essential for proper ecosystem management. The Apalachicola Bay system (ABS) is a large, river-dominated estuary in the northeastern Gulf of Mexico that spans wide environmental gradients due to substantial spatiotemporal variation in fluvial influence, thus supporting diverse habitats and species assemblages. We employed fishery-independent gillnet and longline surveys to describe communities of elasmobranchs and large teleost fishes throughout the ABS. Non-metric multidimensional scaling followed by environmental fitting delineated two distinct regions of the system and identified the environmental parameters as well as fish species that contributed most to the observed variation. Ongoing investigation of trophic structure among the 5 most common shark species in the system will work in conjunction with results from community analysis to provide a current baseline of elasmobranch communities and trophic ecology in the ABS. Modelling of nutrient source contributions to consumer biomass will be explored for these species to infer relative importance of fluvial-based nutrients. We intend to characterize the impact of river-input on fish communities and the importance of allochthonous nutrient sources to elasmobranch biomass, with implications for watershed and fisheries management.

    2.  09:30  IN-PERSON    Defining Sex-specific Habitat Suitability for a Northern Gulf of Mexico Shark Assemblage. Marcus Drymon*, Mississippi State University; Simon Dedman, Stanford; Amanda Jefferson, Mississippi State University; Sean Powers, University of South Alabama

    Understanding factors that influence species’ distributions is crucial for implementing effective management and conservation practices, yet difficult for highly vagile species like sharks. Many shark species demonstrate spatial and/or temporal sexual segregation, further confounding accurate quantification of habitat suitability. We sought to quantify sex-specific abiotic factors that influence seasonal variation in a coastal shark assemblage using data from a long-term fisheries-independent bottom longline program in the northern Gulf of Mexico. Catch data were coupled with a suite of potentially predictive variables and analyzed using boosted regression trees. Between May 2006 and November 2018, we conducted 1,226 bottom longline sets and caught 13,742 individuals encompassing 67 species. Two species from each of the following three categories were selected for further analyses: small coastal sharks (Atlantic sharpnose shark Rhizoprionodon terraenovaeand blacknose shark Carcharhinus acronotus), large coastal sharks (blacktip shark C. limbatus and sandbar shark C. plumbeus), and shelf-associated sharks (smoothhound sharks, Mustelus spp. and scalloped hammerhead Sphyrna lewini). Depth and distance from shore were the strongest predictors of distribution and relative abundance, followed by longitude and bottom salinity. For the six species examined, predictive factors were often the same for males and females, although the range of preferred values varied. Surprisingly, the importance of these predictors varied little across seasons. Collectively, our findings demonstrate that sexual segregation is the norm for sharks in the northern Gulf of Mexico. Long-term fishery-independent monitoring to further quantify these sex-based differences in habitat use should be prioritized, particularly in light of impending climate change.

    3.  09:45  IN-PERSON    Drivers of Community Structure of Coastal Sharks in Everglades National Park and the Florida Keys. Ashley Dawdy*, Florida State University; Cheston Peterson, Florida State University; Dean Grubbs, FSU Coastal & Marine Laboratory

    The Florida Keys and Everglades National Park serve as critical habitat to many taxa and provide a structurally complex ecosystem used for reproduction, development, and feeding by many species, including those that are endangered or vulnerable to overexploitation. A coastal longline survey targeting large juvenile and adult smalltooth sawfish (Pristis pectinata) was established in the Florida Keys in 2011, with fishing locations spanning Everglades National Park, Keys Edge, Coastal Keys, and North Florida Bay. Between January 2011 and April 2021, a total of 681 longline sets were conducted in the Florida Keys across all seasons. A total of 3046 elasmobranchs were captured, including 14 shark species and 2 batoid species, with the most abundant being blacktips (Carcharhinus limbatus), blacknose (Carcharhinus acronotus), and lemon sharks (Negaprion brevirostris), respectively. Elasmobranchs of all life stages and a wide size range were captured, ranging from a young-of-year Atlantic sharpnose (Rhizoprionodon terraenovae) at 38cm to a mature smalltooth sawfish at 468cm. Multivariate analyses were performed to describe the spatial and temporal variation in shark communities in the Florida Keys. Permutational analysis of variance was used to assess differences in shark community structure and sex ratio across season and habitat, and general additive models were used to identify abiotic effects on community structure. An indicator species analysis was performed to identify potential indicator species for each sampling region. Quantifying drivers of community structure is crucial for evaluating changes in communities over time, as well as implementing effective management and species protection strategies for ecologically significant areas.

    4.  10:00  VIRTUAL    Great Blue Heron (Ardea herodias) Predation on an Abnormal California Butterfly Ray (Gymnura marmorata) and its Ecological Implications. Victor Bach Muñoz*, University of Miami

    A Great Blue Heron (Ardea herodias) was observed killing a California Butterfly Ray (Gymnura marmorata) with a morphological abnormality off coastal California. Even though this heron species has previously been reported actively hunting batoids, this observation is the first documenting of an attack by a bird (or any other predator) on a butterfly ray. The behavior observed in this event adds butterfly rays as potential prey items of A. herodias and provides further insights on both this bird’s ecology as a nearshore predator and that of ray species like G. marmorata as important prey. Additionally, this is the first record of a rostral anomaly on G. marmorata, which is consistent with morphological abnormalities previously observed on similar species.

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