Citizen-Sourced Sightings and Underwater Photography Reveal Novel Insights About Green Sea Turtle Distribution and Ecology in Southern California

Abstract

East Pacific (EP) green turtles (Chelonia mydas) have undergone substantial population recovery over the last two decades owing to holistic protection at nesting beaches and foraging areas. At the northern end of their range in southern California United States, green turtles have been seen in more areas and in greater numbers since 2014 than before as a result. A resident population of green turtles has established near La Jolla Shores (LJS), a protected site with daily marine tourism (e.g., kayakers, snorkelers, divers). To study this local aggregation, innovative and non-invasive methods were required because the traditional capture-recapture methods were infeasible due to public relations sensitivities. Green turtle habituation to humans at this site has created a unique opportunity for citizen-based science using underwater photography to document turtles and their surroundings. We obtained 309 usable photographs of local green turtles from members of the dive/snorkel community in LJS. Photos were taken from April 2016 to June 2019. Images were processed in Hotspotter—a patterned species instance recognition software—to identify seven individuals, five of which were consistently photographed throughout that period. These images helped infer minimum residency duration (MRD), seasonal differences in algal coverage on the carapace, habitat association, behavioral patterns, and diet. Mean MRD was 424 days (SE = 131 days, calculated from entire population, n = 7), during which turtles were active in 82.8% of the photographs; the remainder of the photographs depicted foraging (14.9%) or resting behavior (2.3%). Green turtles were seen foraging in water temperatures as low as 15.8°C, the lowest recorded temperature for foraging green turtles documented in literature. Additional opportunistic observational platforms were used to look at trends of increasing green turtle abundance in southern California since 2015 that supported the arrival of a new aggregation of green turtles in LJS. Our use of citizen-sourced photographs confirms the presence of a resident aggregation of green turtles in LJS. Existence of green turtles and other protected species in highly populated areas provide excellent opportunities to educate beachgoers and seafarers about conservation of these species. This study also highlights the value of citizen-based science in areas where traditional research techniques are ill-suited.

Tracking movements and growth of post-hatchling to adult hawksbill sea turtles using skeleto+iso

“…As a result, these traditional methods leave gaps in our knowledge about the movements and life history patterns of these longlived animals. Alternative methods, however, are emerging to help generate and recreate sequential multi-year habitat use data, including photo-identification (Dunbar et al, 2021), often with the help of community scientists (e.g., Hanna et al, 2021), and the combination of skeletochronology (the study of growth layers) with stable isotope analysis "skeleto+iso" (Snover et al, 2010;Avens et al, , 2021Ramirez et al, 2015;Turner Tomaszewicz et al, 2016, 2017a.…”

The urban lives of green sea turtles: Insights into behavior in an industrialized habitat using an animal‐borne camera

“…This hypothesis aligns with our findings, as no symbiotic relationship involving turtles has been observed in SDB. Additionally, shell biofouling in green turtles has been documented year-round at the nearby La Jolla Shores foraging area (30 km NNW from our SDB study site; Hanna et al, 2021) and anecdotal observations suggest that some SDB green turtles face the same challenge, though not to the same level. Additionally, there may be other benefits from this behavior, such as exfoliation.…”

Long-Term Monitoring of In-Water Abundance of Juvenile Pelagic Loggerhead Sea Turtles (Caretta caretta): Population Trends in Relation to North Atlantic Oscillation and Nesting

“…Since whalewatching trips varied little in their trip time, we have essentially a constant-effort scheme (Quinn and Deriso, 1999) and thus a reliable and cost-effective population sampling methodology, for an otherwise challenging oceanic life stage sampling. For turtles, these types of indices have previously been used mainly to access bycatch rates (Coelho et al, 2013;Carlson et al, 2016) and only recently have citizen science studies addressed population distribution and abundance (Hof et al, 2017; Casale et al, 2020;Hanna et al, 2021). It furthermore represents an example of the contribution of ecotourism to conservation.…”