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Water temperature plays a critical role in mediating energy budgets and influencing the behavior of marine ectotherms. Previous research has demonstrated that marine ectotherms such as sea turtles conserve energy by decreasing activity levels in colder water—often at or near the latitudinal limits of their range. San Diego Bay is near the northern edge of the range for eastern Pacific green turtles and is home to a year-round foraging population. Turtles in San Diego Bay experienced a significant decrease in ambient water temperature following the closure of a fossil-fuel-based power plant and corresponding loss of the plant’s warm-water effluent. Time-depth recorders were placed on 13 turtles before (n = 5) and after (n = 8) the closure of this plant to determine how changing water temperature influenced dive duration. Deployments lasted 2-25 d, with a mean deployment of 7.5 d. Green turtle behavior in different thermal regimes revealed a strong relationship between dive duration and water temperature; dive duration was significantly longer when water temperatures were colder, especially when water was below 14.4°C. Establishing the inactivity threshold for this population is critical to future management in light of temperature variability in coastal habitats and the impacts this may have on sea turtle energetics. Understanding organismal response to relatively rapid shifts in thermal conditions is relevant to assessments of the direct and indirect anthropogenic effects on aquatic environments.

Human activities influence the environment on a planetary scale and have led to an overall trend of global warming worldwide. Power generating plants have emerged as unlikely candidates to study the effects of temperature change on aquatic organisms, like sea turtles. Industrial power plants that utilize once-through cooling (OTC) systems discharge thermal effluent into freshwater and/or marine environments, and the heated discharge often significantly affects the local habitat, creating an unnatural thermal ecology. These types of power plants are common around the world, and their effects on local ecosystems are comparable making them opportune study sites. This chapter discusses the effects of thermal effluent on thermoregulation of aquatic reptiles like the sea turtles, with focus on the green turtles in San Diego Bay.

Bet-hedging theory makes the counter-intuitive prediction that, if juvenile survival is low and unpredictable, organisms should consistently reduce short-term reproductive output to minimize the risk of reproductive failure in the long-term. We investigated the long-term reproductive output of an Agassiz's desert tortoise (Gopherus agassizii) population and conformance to a bet-hedging strategy of reproduction in an unpredictable but comparatively productive environment. Most females reproduced every year, even during periods of low precipitation and poor germination of food plants, and the mean percentage of reproducing females did not differ significantly on an annual basis. Although mean annual egg production (clutch size × clutch frequency) differed significantly among years, mean clutch size and mean clutch frequency remained relatively constant. During an El Nino year, mean annual egg production and mean annual clutch frequency were the highest ever reported for this species. Annual egg production was positively influenced by maternal body size but clutch size and clutch frequency were not. Our long-term results confirm earlier conclusions based on short-term research that desert tortoises have a bet-hedging strategy of producing small clutches almost every year. The risk of long-term reproductive failure is minimized in unpredictable environments, both through time by annually producing multiple small clutches over a long reproductive lifespan, even in years of low resource availability, and through space by depositing multiple annual clutches in different locations. The extraordinary annual reproductive output of this population appears to be the result of a typically high but unpredictable biomass of annual food plants at the site relative to tortoise habitat in dryer regions. Under the comparatively productive but unpredictable conditions, tortoises conform to predictions of a bet-hedging strategy of reproduction with relatively small but consistent clutch sizes. Published 2015. This article is a U.S. Government work and is in the public domain in the USA, Biological Journal of the Linnean Society, 2015, 115, 399–410.

Protection of endangered species requires an understanding of their spatial ecology in relation to human activities. Recent improvements in monitoring technologies, such as automated acoustic telemetry, have enabled the collection of these data for mobile marine organisms such as sea turtles. The east Pacific green sea turtle Chelonia mydas uses San Diego Bay, CA, a heavily developed ecosystem, as a year-round foraging ground. We used a combination of manual and automated acoustic telemetry from 2009 to 2011 to elucidate the distribution of green turtles throughout South San Diego Bay and to understand their diel behavior. Tracked turtles (n = 20) ranged in size from 54.9 to 102.5 cm straight carapace length and had fidelity to two sites: the warm-water effluent channel of a waterfront power plant and an eelgrass meadow. Turtles tracked manually during the night were more sedentary (mean swimming speed ± SE: 0.38 ± 0.03 km h− 1) and generally restricted their activity to waters near the power plant. During the day, turtles swam at higher speeds (0.67 ± 0.07 km h− 1) and were mainly found in eelgrass meadows where they are known to forage. Turtles were occasionally found near a shipping terminal, which occurred almost exclusively during the daytime. Turtles in areas of increased boat traffic are at risk of vessel strikes, and future monitoring should investigate the potential for turtle–human interactions in other heavily-used areas of San Diego Bay. Future monitoring should also characterize how turtle behavior may change following the decommissioning of the power plant, which occurred six months before the end of this study.

There is concern about how climate change might affect Agassiz's desert tortoise Gopherus agassizii, a threatened species. We studied the effects of climatic variation on clutch phenology of a population at a wind energy generation facility for 7 field seasons between 1997 and 2011. Using X-radiography, we quantified the following phenophases based on the number of calendar days to each event from 1 January: appearance and disappearance of 65 first and 53 sec- ond clutches, and inter-clutch intervals between first and second clutches. Although third clutches were rare (n = 8), they were observed in 5 of 7 yr and were produced by 8 different females, all of which produced a third clutch only once during the study. Shelled eggs were visible from as early as 11 April to as late as 28 July, and the overall time span that eggs were visible differed among years. After controlling for maternal effects, we observed statistically significant inter-annual vari- ation in all phenophases except for inter-clutch interval. Clutch appearance was late in cool years relative to warm years and especially late after 2 consecutive cool years. Using degree day (DD) methodology, we calculated DD accumulation during the post-hibernation and nesting season for each year. We then used DD estimates for mean date of first clutch appearance to predict the mean date of first clutch appearance in subsequent years with 1 to 10 d accuracy for all but 1 yr (1998) with El Nino conditions. Clutch phenology appears to be correlated with inter-annual variation in climate and may be influenced by climatic events in previous years.

Green sea turtles Chelonia mydas use coastal areas as foraging grounds for the majority of their lives. Human development of coastlines is increasing, but the effects of urban development of foraging grounds on green turtles are poorly understood. We used acoustic telemetry to determine home ranges of green turtles during 2009 to 2011 in San Diego Bay, Cali- fornia, USA, which is a highly urbanized temperate foraging area. Adult and juvenile turtles (n = 25, straight carapace length = 54.9 to 102.5 cm) were tracked for up to 370 d. Based on the fixed kernel densities of 15 turtles, we found individual home range areas (95% utilization distribution) were 2.09 to 8.70 km 2 (mean ± SE = 5.51 ± 0.57 km 2 ), where each turtle used 1 or 2 core activity areas (50% utilization distribution). The home ranges of all turtles were exclusively in the south- ern portion of San Diego Bay, where eelgrass Zostera marina is abundant and where human activ- ity is the lowest within the bay. Core activity areas coincided with eelgrass distribution or occurred adjacent to the warm water-effluent outfall of a power plant. Results from our study suggest that south San Diego Bay serves as important turtle habitat within the bay. Future monitoring is required to document the potential effects of changing environmental conditions, including closure of the power plant, on green turtles residing in San Diego Bay.

We studied the reproductive ecology of female Sonora mud turtles (Kinosternon sonoriense) at Montezuma Well, a chemically-challenging natural wetland in central Arizona, USA. Females matured between 115.5 and 125 mm carapace length (CL) and 36-54% produced eggs each year. Eggs were detected in X-radiographs from 23 April-28 September (2007-2008) and the highest proportion (56%) of adult females with eggs occurred in June and July. Clutch frequency was rarely more than once per year. Clutch size was weakly correlated with body size, ranged from 1-8 (mean = 4.96) and did not differ significantly between years. X-ray egg width ranged from 17.8-21.7 mm (mean 19.4 mm) and varied more among clutches than within. Mean X-ray egg width of a clutch did not vary significantly with CL of females, although X-ray pelvic aperture width increased with CL. We observed no evidence of a morphological constraint on egg width. In addition, greater variation in clutch size, relative to egg width, suggests that egg size is optimized in this hydrologically stable but chemically-challenging habitat. We suggest that the diversity of architectures exhibited by the turtle pelvis, and their associated lack of correspondence to taxonomic or behavioral groupings, explains some of the variation observed in egg size of turtles.

We studied the long-term response of a cohort of eight female Agassiz’s desert tortoises (Gopherus agassizii) during the first 15 years following a large fire at a wind energy generation facility near Palm Springs, California, USA. The fire burned a significant portion of the study site in 1995. Tortoise activity areas were mapped using minimum convex polygons for a proximate post-fire interval from 1997 to 2000, and a long-term post-fire interval from 2009 to 2010. In addition, we measured the annual reproductive output of eggs each year and monitored the body condition of tortoises over time. One adult female tortoise was killed by the fire and five tortoises bore exposure scars that were not fatal. Despite predictions that tortoises would make the short-distance movements from burned to nearby unburned habitats, most activity areas and their centroids remained in burned areas for the duration of the study. The percentage of activity area burned did not differ significantly between the two monitoring periods. Annual reproductive output and measures of body condition remained statistically similar throughout the monitoring period. Despite changes in plant composition, conditions at this site appeared to be suitable for survival of tortoises following a major fire. High productivity at the site may have buffered tortoises from the adverse impacts of fire if they were not killed outright. Tortoise populations at less productive desert sites may not have adequate resources to sustain normal activity areas, reproductive output, and body conditions following fire.

Culverts are often used to increase the permeability of roaded landscapes for wildlife, including turtles. Although the benefits of culverts as safe passages for turtles are well documented, under some conditions culverts can entrap them and cause mortality. Here we report a culvert-related mortality in the federally threatened desert tortoise (Gopherus agassizii) at a wind energy facility in California and offer simple recommendations to mitigate the negative effects of culverts for wildlife in general.

The South Florida subpopulation of loggerhead sea turtles (Caretta caretta L.) nests with great fidelity on either the southeast or the southwest coast of Florida, USA. The hatchlings that emerge from those nests must swim in opposite directions and search for different surface currents to migrate away from continental shelf waters. In this laboratory study, we compared the pattern of swimming activity shown by the hatchlings from each coast over the first 6 days of migration. Turtles from both coasts were equally active during their “frenzy” period (the first 24 h of swimming) and during the daylight hours of the 5 days that followed (the “postfrenzy” period). However, the west coast turtles were significantly more active than the east coast turtles during the nocturnal portion of the postfrenzy period. This difference may be related to the greater distance southwest coast turtles must negotiate to locate surface currents for transport out of the Gulf of Mexico and into the Atlantic Ocean basin. These differing behavioral strategies may be genetically determined, as similar correspondence between activity and distance is well known among migratory populations of birds and fish and is often based upon inherited programs of endogenously driven activity. Alternatively, behavioral differences between the two nesting groups could be a manifestation of phenotypic plasticity that arises as the hatchlings respond to unique environmental cues on each coast.

With the recent increase in utility-scale wind energy development, researchers have become increasingly concerned how this activity will affect wildlife and their habitat. To understand the potential impacts of wind energy facilities (WEF) post-construction (i.e., operation and maintenance) on wildlife, we compared differences in activity centers and survivorship of Agassiz’s desert tortoises (Gopherus agassizii) inside or near a WEF to neighboring tortoises living near a wilderness area (NWA) and farther from the WEF. We found that the size of tortoise activity centers varied, but not significantly so, between the WEF (6.25 ± 2.13 ha) and adjacent NWA (4.13 ± 1.23 ha). However, apparent survival did differ significantly between the habitat types: over the 18-year study period apparent annual survival estimates were 0.96 ± 0.01 for WEF tortoises and 0.92 ± 0.02 for tortoises in the NWA. High annual survival suggests that operation and maintenance of the WEF has not caused considerable declines in the adult population over the past two decades. Low traffic volume, enhanced resource availability, and decreased predator populations may influence annual survivorship at this WEF. Further research on these proximate mechanisms and population recruitment would be useful for mitigating and managing post-development impacts of utility-scale wind energy on long-lived terrestrial vertebrates.

Context There is little information available on how research activities might cause stress responses in wildlife, especially responses of threatened species such as the desert tortoise (Gopherus agassizii). Aims The present study aims to detect behavioural effects of researcher handling and winter precipitation on a natural population of desert tortoises in the desert of Southwestern United States, over the period 1997 to 2014, through extensive assessments of capture events during multiple research studies, and capture–mark–recapture survivorship analysis. Methods Juvenile and adult desert tortoises were repeatedly handled with consistent methodology across 18 years during 10 study seasons. Using a generalised linear mixed-effects model, we assessed the effects of both research manipulation and abiotic conditions on probability of voiding. Additionally, we used a Cormack–Jolly–Seber model to assess the effects of winter precipitation and voiding on long-term apparent survivorship. Key results Of 1008 total capture events, voiding was recorded on 83 (8.2%) occasions in 42 different individuals. Our top models indicated that increases in handling time led to significantly higher probabilities of voiding for juveniles, females and males. Similarly, increases in precipitation resulted in significantly higher probabilities of voiding for juveniles and females, but not for males. Tortoise capture frequency was negatively correlated with voiding occurrence. Cormack–Jolly–Seber models demonstrated a weak effect of winter precipitation on survivorship, but a negligible effect for both voiding behaviour and sex. Conclusions Handling-induced voiding by desert tortoises may occur during common research activities and years of above average winter precipitation. Increased likelihood of voiding in individuals with relatively low numbers of recaptures suggested that tortoises may have perceived researchers initially as predators, and therefore voided as a defensive strategy. Voiding does not appear to impact long-term survivorship in desert tortoises at this site. Implications This study has demonstrated that common handling practices on desert tortoise may cause voiding behaviour. These results suggest that in order to minimise undesirable behavioural responses in studied desert tortoise populations, defined procedures or protocols must be followed by the investigators to reduce contact period to the extent feasible.

Ocean water temperature is changing as a result of anthropogenic influences on the marine environment. 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-wintering 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. 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. 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 temperatures. 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.