Elasmobranch Use of Nearshore Estuarine Habitats Responds to Fine-Scale, Intra-Seasonal Environmental Variation: Observing Coastal Shark Density in a Temperate Estuary Utilizing Unoccupied Aircraft Systems (UAS)

Alexandra E Digiacomo,Justin T Ridge,David W Johnston,Walker E Harrison

doi:10.3390/drones4040074

Alexandra E Digiacomo, Justin T Ridge + Show 2 more

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https://doi.org/10.3390/drones4040074

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Journal: Drones	Publication Date: Dec 8, 2020
Citations: 4	License type: CC BY 4.0

Affiliation: Marine Conservation Institute, Duke University

Abstract

Many coastal shark species are known to use estuaries of the coastal southeastern United States for essential purposes like foraging, reproducing, and protection from predation. Temperate estuarine landscapes, such as the Rachel Carson Reserve (RCR) in Beaufort, NC, are dynamic habitat mosaics that experience fluctuations in physical and chemical oceanographic properties on various temporal and spatial scales. These patterns in abiotic conditions play an important role in determining species movement. The goal of this study was to understand the impact of environmental conditions around the RCR on shark density within the high-abundance summer season. Unoccupied Aircraft System (UAS) surveys of coastal habitats within the reserve were used to quantify shark density across varying environmental conditions. A combination of correlation analyses and Generalized Linear Modelling (GLM) revealed that density differs substantially across study sites and increases with rising water temperatures, conclusions that are supported by previous work in similar habitats. Additionally, density appears to increase moving towards dawn and dusk, potentially supporting crepuscular activity in coastal estuarine areas. By describing shark density dynamics in the RCR, this study provides new information on this population and presents a novel framework for studying elasmobranchs in temperate estuaries.

Highlights

Estuarine and coastal ecosystems of the southeastern United States are rich in both species’diversity and abundance [1]
By describing shark density dynamics in the Rachel Carson Reserve (RCR), this study provides new information on this population and presents a novel framework for studying elasmobranchs in temperate estuaries
This study provides new information about shark density dynamics within the RCR, an area frequented by tourists and locals for recreation

Summary

Introduction

Estuarine and coastal ecosystems of the southeastern United States are rich in both species’diversity and abundance [1]. Salt marshes and oyster reefs characteristic of southeastern coastlines support the maintenance of commercial and recreational fisheries by providing reproductive space, nursery grounds, and plentiful foraging habitat for fish. Coastal areas only account for 4% of earth’s total land surface area, they are inhabited by more than 30% of the world’s human population [3]. Considering that these areas are twice as densely populated as their inland counterparts, marine coastal zones and the resident species are vulnerable to anthropogenic effects, including increased direct human interactions with marine wildlife [3].

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