Articles
We've read a variety of research articles about the lagoons and coastal areas of San Diego County. For several of us on the iLagoons team, our marine science interests include a specific interest in sea turtle conservation. Did you know that sea turtles live in and migrate through the Southern California coastal areas? Read some of these research articles to learn more!
Monitoring Green Sea Turtles in the San Gabriel River of Southern California
Authors: Lynn M. Massey, Shannon Penna, Eric Zahn, Dan Lawson, and Cassandra M. Davis
Download link: https://www.mdpi.com/2076-2615/13/3/434
Summary: "The East Pacific population of green sea turtles (Chelonia mydas) has undergone substantial growth in recent years, and as such, green sea turtle sightings are becoming more common along the U.S. West Coast. The northernmost resident population of green sea turtles in the eastern Pacific Ocean lives near the mouth of the San Gabriel River in Long Beach, California, USA. Utilizing nine years (2013–2021) of citizen science data from the Aquarium of the Pacific’s Southern California Sea Turtle Monitoring Project, we established a year-round presence of this population and determined that the areas along a 2.4-km (1.5 mile) stretch of the lower San Gabriel River with the most green sea turtle activity are near the Los Cerritos Wetlands and a power plant warm water effluent area, which are located approximately 1.3 and 2.9 km (0.8 and 1.8 miles), respectively, upriver from the mouth and entrance to Alamitos Bay. We hypothesize that turtles are attracted to these areas of the river for forage opportunity and thermal refuge. As green sea turtle presence in Southern California continues to increase, we recommend expanded monitoring programs to help understand essential habitat needs for this threatened population."
Citation: Massey, L.M.; Penna, S.; Zahn, E.; Lawson, D.; Davis, C.M. Monitoring Green Sea Turtles in the San Gabriel River of Southern California. Animals 2023, 13, 434. https://doi.org/10.3390/ ani13030434
Characterizing response of East Pacific
green turtles to changing temperatures: using acoustic telemetry in a highly urbanized environment
Authors: Sheila V. Madrak, Rebecca L. Lewison, Jeffrey A. Seminoff and Tomoharu Eguchi
Download link:
https://animalbiotelemetry.biomedcentral.com/articles/10.1186/s40317-016-0114-7
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Abstract
"Background: Ocean water temperature is changing as a result of anthropogenic influences on the marine envi- ronment. Highly mobile marine ectotherms, such as sea turtles, may be particularly susceptible to these changes. However, our current understanding of location-specific thermal tolerances, especially at coastal foraging or over-win- tering areas, is limited. Human-induced changes, such as thermal effluent from power plants, appear to have a suite of influences on species that reside in affected areas. Here, we describe a study of green turtle habitat use related to changing water temperature at a coastal foraging site that has recently experienced a power plant closure, leading to a transition to cooler ambient water temperature. We used a combination of active and passive acoustic telemetry to monitor green turtle distribution in relation to water temperature in this dynamic thermal environment.
Results: Both before and after closure of the power plant, turtles were distributed in significantly warmer waters than surrounding environments during winter months (December–February). Turtles in winter were rarely detected in water temperatures lower than 14.5 °C. Body size was negatively correlated with water temperature after closure of the power plant, with larger turtles found in cooler waters, while smaller turtles remained within warmer areas. There was not a significant relationship between body size and water temperature before closure of the power plant as water temperature was more constant during operation.
Conclusions: Green turtles in San Diego Bay experienced a shift in water temperature following the loss of thermal effluent from a power plant. The effects of this shift were particularly evident during winter months, when ambient water temperatures were coolest. Water temperatures in the southern region of San Diego Bay were significantly warmer during winter before the closure of the power plant, and turtles were detected in significantly warmer water. Turtles in San Diego Bay may associate with or seek out thermal refugia, when possible, to avoid low water tempera- tures. The cold water temperature inactivity threshold for East Pacific green turtles may be lower than previously thought. There was a significant negative relationship between turtle size and water temperature after power plant closure. East Pacific green turtles exhibit clear responses in habitat use to changes in water temperature at a foraging site near the edge of their geographic range."
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Citation: Madrak, S.V., Lewison, R.L., Seminoff, J.A. et al. Characterizing response of East Pacific green turtles to changing temperatures: using acoustic telemetry in a highly urbanized environment. Anim Biotelemetry 4, 22 (2016). https://doi.org/10.1186/s40317-016-0114-7
Citizen-Sourced Sightings and Underwater Photography Reveal Novel Insights About Green Sea Turtle Distribution and Ecology in Southern California
Authors: Megan E. Hanna, Erin M. Chandler, Brice X. Semmens, Tomoharu Eguchi, Garrett E. Lemons and Jeffrey A. Seminoff
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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 15.8â—¦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."
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Citation: Hanna ME, Chandler EM, Semmens BX, Eguchi T, Lemons GE and Seminoff JA (2021) Citizen-Sourced Sightings and Underwater Photography Reveal Novel Insights About Green Sea Turtle Distribution and Ecology in Southern California. Front. Mar. Sci. 8:671061. doi: 10.3389/fmars.2021.671061
Finding Crush: Environmental DNA Analysis as a Tool for Tracking the Green Sea Turtle Chelonia midas in a Marine Estuary
Authors: Kirsten J. Harper, Kelly D. Goodwin, Lynsey R. Harper, Erin L. LaCasella, Amy Frey, and Peter H. Dutton
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Abstract: "Environmental DNA (eDNA) analysis is a rapid, non-invasive method for species detection and distribution assessment using DNA released into the surrounding environment by an organism. eDNA analysis is recognised as a powerful tool for detecting endangered or rare species in a range of ecosystems. Although the number of studies using eDNA analysis in marine systems is continually increasing, there appears to be no published studies investigating the use of eDNA analysis to detect sea turtles in natural conditions. We tested the efficacy of two primer pairs known to amplify DNA fragments of differing lengths (488 and 253 bp) from Chelonia mydas tissues for detecting C. mydas eDNA in water samples. The capture, extraction, and amplification of C. mydas eDNA from aquaria (Sea World, San Diego, CA, United States) and natural water (San Diego Bay, CA, United States) were successful using either primer set. The primer pair providing the shorter amplicon, LCMint2/H950g, demonstrated the ability to distinguish cross-reactive species by melt curve analysis and provided superior amplification metrics compared to the other primer set (LTCM2/HDCM2); although primer dimer was observed, warranting future design refinement. Results indicated that water samples taken from deeper depths might improve detection frequency, consistent with C. mydas behaviour. Overall, this pilot study suggests that with refinement of sampling methodology and further assay optimisation, eDNA analysis represents a promising tool to monitor C. mydas. Potential applications include rapid assessment across broad geographical areas to pinpoint promising locations for further evaluation with traditional methods."
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Citation: Harper KJ, Goodwin KD, Harper LR, LaCasella EL, Frey A and Dutton PH (2020) Finding Crush: Environmental DNA Analysis as a Tool for Tracking the Green Sea Turtle Chelonia mydas in a Marine Estuary. Front. Mar. Sci. 6:810. doi: 10.3389/fmars.2019.00810
Effects of a Power Plant Closure on Home Ranges of Green Turtles in an Urban Foraging Area
Authors: Tomoharu Eguchi, Jessica Bredvik, and J. Seminoff
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Abstract: "A natural experiment was conducted to determine effects of a fossil-fueled power plant on home ranges of east Pacific green turtles Chelonia mydas in an urban foraging ground. The power plant, located in south San Diego Bay, California, USA, co-existed with a resident for- aging aggregation of ~60 green turtles for ~50 yr. It was decommissioned during a long-term green turtle monitoring study, thus providing a rare opportunity to evaluate how the cessation of warm-water effluent affected turtle movements and habitat use in the area. During pre- and post- decommissioning of the power plant, 7 and 23 green turtles, respectively, were equipped with GPS-enabled satellite transmitters. Useful data were obtained from 17 turtles (4 for pre- and 13 for post-decommissioning). Core use areas (50% utilization distribution [UD]) increased from 0.71 to 1.37 km2 after the power plant decommissioning. Increase in post-power plant 50% UD was greater during nighttime (0.52 to 1.44 km2) than daytime (1.32 to 1.43 km2). Furthermore, UDs moved from the effluent channel to an area closer to seagrass pastures, a presumed foraging habi- tat of the turtles. The observed expansion of green turtle home ranges may increase turtle−human interactions, such as boat strikes, within the foraging ground; this underscores how seemingly innocuous human actions contribute to inadvertent consequences to wildlife. Possible manage- ment and conservation actions include increasing awareness of the public regarding turtle pres- ence in the area through signage and education as well as legislating for a reduction in boat speeds in select areas of the bay."
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Citation: Eguchi, T., Bredvik, J., Graham, S., LeRoux, R.A., Saunders, B., & Seminoff, J.A. (2020). Effects of a power plant closure on home ranges of green turtles in an urban foraging area. Endangered Species Research, 41, 265-277.
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