Using a photogrammetric mark-recapture approach to denote sea turtle encounters within the northern Gulf of Mexico

Link To Share This Poster: https://cdmcd.co/kgyPzM
Live Discussion Link: https://cdmcd.co/WkzLAJ

Emma Roberto, Jackson Reimer, Tabitha Siegfried and Susan E. Piacenza, Biology, University of West Florida, Pensacola, FL

Background/Question/Methods
Identifying sea turtles individually is vital to understand their ecological importance within shallow environments, and aids towards conservation efforts for these endangered species. In-water intraspecific surveying indicates re-sightings, which allows us to understand site fidelity and habitat preference. Photogrammetry is one method that intraspecifically identifies individuals by denoting unique markings along their body. In this study, we used photogrammetry to target loggerhead (Caretta caretta), green (Chelonia mydas), and Kemp’s ridley sea turtles (Lepidochelys kempii) from May 2019-July 2020 to contribute to a mark-recapture database, as these species are commonly encountered during stereo-video camera system surveys (SVCS) in the northern Gulf of Mexico. We conducted in-water surveys along 13 shallow natural habitats and artificial reefs within the Florida Panhandle via snorkeling using a handheld action camera to collect footage of facial scales to establish individual identity. We concurrently conducted stereo-video camera surveys to estimate straight carapace length (SCL). Still images of each individual’s facial profile were obtained to characterize scale shape, size, and pigmentation. We utilized freely available online programs for photo identification (Internet of Turtles, I3S). The re-sighting data was analyzed to understand site fidelity, how individuals may be using multiple sites, and to detect differences in habitat type usage.
Results/Conclusions
Out of 54 turtle encounters from May 2019-July 2020, a total of 4 were re-sighted: 2 individuals were re-sighted once, and 2 individuals were re-sighted with two encounters at Navarre and Park East reef. Based on SCL measurements, which ranged between 47.6-59.5 cm, all turtles re-sighted were juveniles. Three of the individuals were green sea turtles, which were re-sighted at the same reef in which they were originally encountered. However, the timespan in which each individual demonstrated site fidelity ranged from one day to 5 months. The fourth individual was a Kemp’s ridley sea turtle, which migrated 12.2 miles between Navarre reef to Park East reef within one day. Navarre reef appears to be a favored site, as 6 out of the 10 re-sighting events occurred there. The ratio of turtle encounters to re-sighted individuals (54:4) demonstrates that site fidelity is low within the artificial reefs. However, the high number of new encounters indicates juvenile turtles are ontogenetically shifting to various habitats. As few turtles appear to be residents at the artificial reefs in Northwest Florida, it seems likely that juvenile sea turtles are using this habitat as transient resources for rest, foraging, and self-cleaning purposes.