Using a Stereo-video Camera System to Remotely Measure Sea Turtle Morphometrics in Situ

Emma Roberto

Sea turtle morphometrics have long been studied to yield insight into demography, life history, and conservation status. While collecting manual morphometric data is imperative to provide insight in conserving sea turtle species globally, methods in obtaining manual parameters are often invasive and not generally standardized due to measurement variation. One way to solve this issue is by using remote sensing technology, such as a stereo-video camera (SVC) system, as it is an advantageous tool in the collection of accurate, remote data and allows for obtaining morphometric parameters non-intrusively. This study focused on examining various sea turtle morphometrics and biomass data of green sea turtles (Chelonia mydas), loggerhead sea turtles (Caretta caretta), and Kemp’s ridley sea turtles (Lepidochelys kempii) within the northern Gulf of Mexico (nGoM) by remotely measuring body lengths using a SVC system. First, a revised morphometric guide was provided that suggests manual and remote techniques to measure and standardize non-conventional sea turtle morphometric parameters. In order to validate that all non-conventional morphometrics were accurate relative to their manual lengths, the accuracy of each parameter was tested by measuring 70 juvenile (n = 41), subadult (n = 22), and adult (n = 7) sea turtles across three species that resided in marine and rehabilitation facilities in Florida. Then, species-specific models were formulated to determine which morphometrics contribute to accurate remote estimations of sea turtle biomass using the generalized linear models (GLM) and information theoretic approach to model selection. For all sea turtle species, the results indicated that straight carapace length (SCL) and head depth (HD) were important parameters for estimating biomass, as each of these explanatory variables were included in the species-specific top-ranked models. For L. kempii, body depth (BD) was an additional parameter included in the top-ranked model, and the width of the left rear flipper (WRFL) was included as an additional parameter for C. caretta. Mean percent bias across all remote measurements for all species ranged from -21.08% (± 6.03 SE) - 11.12% (± 1.41 SE), with a mean of -1.74%. Then, the SVC system was used to assess the three species of sea turtle biomass in situ across shallow artificial reef sites located along the Florida panhandle. Sea turtle biomass, across all three species, was greatest at Topsail Hill, but lowest at Park East. Patterns of sea turtle biomass tended to diverge from body length; however, mean body length was greatest at Topsail Hill. Based on the GAM analysis, sea turtle mean total biomass generally remained the same with increasing mean reef depth, but increased with mean water temperature. Data suggest that sea turtles from the juvenile to adult life stages are often frequenting the artificial reefs, with site fidelity extremely low (based on photo identification) and biomass high at locations that are located farther away from public beach access (based on measuring the distance from the beach entrance to the reef). However, more long-term data needs to be collected to understand biomass trends in relation to sea turtle ecology and health status. This research highlights the value of SVCs as a tool to non-invasively study sea turtles in situ across a variety of habitats in the nGoM to estimate biomass.

Using a Stereo-video Camera System to Remotely Measure Sea Turtle Morphometrics in Situ

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Using a Stereo-video Camera System to Remotely Measure Sea Turtle Morphometrics in Situ

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