Using Aerial Photogrammetry to Assess Stock-Wide Marine Turtle Nesting Distribution, Abundance and Cumulative Exposure to Industrial Activity

Abstract

The lack of accurate distribution maps and reliable abundance estimates for marine species can limit the ability of managers to design scale-appropriate management measures for a stock or population. Here, we tested the utility of aerial photogrammetry for conducting large-scale surveys of nesting marine turtles at remote locations, with a focus on the flatback turtle (Natator depressus) in the Pilbara region of Western Australia. Aerial surveys were conducted between 29 November and 6 December 2016 to overlap with the peak nesting season for flatback turtles and collected imagery was used to examine marine turtle distribution, abundance, and cumulative exposure to industrial activity relative to overlap with protected areas. Two observers independently reviewed aerial georeferenced photographs of 644 beaches and recorded turtle tracks and other evidence of turtle nesting activity. A total of 375 beaches showed signs of nesting activity by either flatback, green (Chelonia mydas) or hawksbill (Eretmochelys imbricata) turtles. Most of these beaches (85.3%) were located on islands, and the rest (14.7%) on the mainland. Half (n = 174) of the active beaches showed evidence of fresh (0–36 h. old) flatback nesting activity, with track abundance varying from 1.0 to 222.0 tracks.night−1. Six rookeries accounted for 62% of the Pilbara flatback stock. Remarkably, 77% of identified flatback rookeries occurred within protected areas. However, one-third (34%) of those were also located within 5 km of a major industrial site, including eight of the highest abundance beaches (50–250 tracks.night−1). Several key rookeries were also identified as being relatively unexposed to industry-related pressures but currently unprotected, highlighting the need for a cumulative impact assessment to be completed for this flatback stock. Finally, our aerial tallies and multiple ground-survey flatback track tallies were highly correlated and together with low intra- and inter-observer errors suggested that reliable data can be collected via aerial photogrammetry for nesting marine turtles. Such large-scale digitized surveys can therefore be used to assess the cumulative exposure of marine turtles to pressures, and to reveal new conservation opportunities.

Vulnerability of sea turtle nesting sites to erosion and inundation: A decision support framework to maximize conservation

“…The model calculated an exposure index for each shoreline section within an area of interest (AOI) using the geometric mean of the ranks for each variable (Appendix S1: Equation S1) (Arkema et al, 2013;Cunha et al, 2021;Sharp et al, 2014). The geometric mean is a Beaches with an unquantified number of old flatback turtle tracks and/or tracks from green and/or hawksbill turtles (Fossette et al, 2021).…”

“…We did this by calculating an exposure index for the region's coastline and coupled this with information on the distribution and abundance of sea turtle nesting activity. Globally, flatback turtles have the smallest nesting distribution relative to other extant sea turtle species (Pike, 2013), and their nesting sites in the Pilbara region are potentially exposed to industry‐related pressures, such as artificial light and coastal development (Fossette et al, 2021; Kamrowski et al, 2012; Pendoley, 2005). These pressures, coupled with an anticipated increase in the frequency and severity of extreme weather events under future climates (Bernstein et al, 2008; Knutson et al, 2020), mean that predicting the vulnerability of these important nesting sites is a vital step toward maintaining the ongoing viability of this species.…”

First Assessment of Mercury (Hg) Concentrations in Skin and Carapace of Flatback Turtles (Natator depressus) (Garman) From Western Australia

“…Flatback turtles nest on Thevenard Island from November to February. The island represents a medium-size nesting site for flatback turtles (Whittock et al, 2016;Fossette et al, 2021) and has been declared a Nature Reserve. The Department of Biodiversity, Conservation and Attractions (DBCA) in WA started the North West Shelf Flatback Turtle Conservation Program in 2011, which implements population studies through track counts and mark-recapture.…”

“…In Western Australia (WA), Thevenard Island and Eighty Mile Beach are important nesting rookeries (nesting sites) for flatback turtles (Fossette et al, 2021). In the last decade, the mining sector has committed to an ongoing structured program of exploration and production activity in parts of WA (Keesing et al, 2018), including the Pilbara region, where Thevenard island is located.…”

Reducing the Impact of Tagging on Flatback Turtles Using Double Passive Integrated Transponder Tags

“…Seven genetic stocks have been identified, with 5 of them located in Western Australia (FitzSimmons et al 2020). In Western Australia, nesting extends from the Muiron Islands in the southwest to Cape Domett in the northeast, with most islands and large parts of the mainland coastline used as rookeries (Pendoley et al 2016; Fossette et al 2021; Tucker et al 2021). Flatback turtles are being monitored and tagged by 4 monitoring groups at 8 locations encompassing 7 rookeries from 2 different stocks and 1 foraging ground.…”