The nest environment influences various aspects of hatchling development in reptiles, sea turtles in particular. The interaction between the biotic (e.g., soil microorganisms and the developing embryo) and abiotic (e.g., sand characteristics, moisture levels, temperature, and gas exchange) factors in a nest makes the nest environment unique and different from the surrounding beach environment (Ackerman 1997). Thus, variations in these factors can influence various hatchling parameters involving morphology and locomotor performance. Nest temperature also determines hatchling sex, with temperatures warmer than the pivotal temperature producing females (Yntema and Mrosovsky 1980). Therefore, there is a concern that increasing sand temperatures and, consequently, nest temperatures in the past few decades has resulted in a female bias in sex ratios in sea turtle populations around the world (Chu et al. 2008; Katselidis et al. 2012; Jensen et al. 2018).

In addition, environmental factors, such as temperature and moisture availability, can influence life history parameters, such as embryonic developmental processes, incubation period, hatchling size, carapace scute pattern, oxygen consumption, and locomotor performance in sea turtles (Booth and Astill 2001; Booth 2006; Burgess et al. 2006; Ischer et al. 2009; Sim et al. 2014, 2015). Although it varies among species, nest temperatures between 29°C and 32°C were found to be optimal for the successful development of embryos, with temperatures above and below this range having a significant effect on hatching success, hatchling morphology, and locomotor performance (Booth et al. 2004, 2013; Maulany et al. 2012; Read et al. 2012; Sim et al. 2015). Thus, changing climate can have a detrimental effect on population demography through multiple pathways, such as sex ratio bias, changes in hatchling morphology and performance, and overall recruitment and survival of hatchlings.

Nest incubation temperature affects the biochemical reactions that govern the developmental process of embryos (Booth 2017). Temperature of the nest can influence nutrient mobilization, hatchling size, water exchange of eggs, tissue hydration, tissue conversion, and energy reserves in hatchlings (Hewavisenthi and Parmenter 2001). Higher nest temperatures tend to reduce the incubation period (Booth 2017), thus allowing less time for yolk material to be converted into hatchling tissue, resulting in smaller hatchlings (Booth et al. 2004; Burgess et al. 2006; Ischer et al. 2009; Maulany et al. 2012; Read et al. 2012; Wood et al. 2014; Sim et al. 2015; Booth 2017). However, smaller hatchlings have more residual yolk mass since less yolk material is converted into tissue. Thus, hatchlings produced at higher temperatures have larger energy reserves as a result of the high residual yolk mass compared with those produced at lower temperatures (Hewavisenthi and Parmenter 2001; Booth et al. 2004; Burgess et al. 2006; Ischer et al. 2009). This is considered as a trade-off between size and energy reserves (Ischer et al. 2009; Booth 2017). The survival advantage for hatchlings will then depend on the posthatching environment (Ischer et al. 2009).

Nest incubation temperatures also influence the locomotor performance of hatchlings. Similar to the temperature range influencing hatchling morphology, higher temperatures were found to affect hatchling crawl speed, righting ability, and swimming performance (Reece et al. 2002; Booth et al. 2004; Burgess et al. 2006; Chu et al. 2008; Ischer et al. 2009; Booth and Evans 2011; Maulany et al. 2012; Sim et al. 2015). Studies on the influence of temperature on locomotor performance of hatchlings suggest that the smaller hatchlings produced at higher incubation temperatures have poorer locomotor ability as a result of smaller body size and flipper length, resulting in smaller strides (Burgess et al. 2006; Chu et al. 2008; Ischer et al. 2009; Booth and Evans 2011; Maulany et al. 2012; Read et al. 2012; Booth et al. 2013). However, the effect of nest temperature on hatchling locomotor ability shows interspecific and intraspecific variation (Chung et al. 2009; Fisher et al. 2014; Mueller et al. 2019; Usategui-Martín et al. 2019; Le Gouvello et al. 2020). In green sea turtles, larger hatchlings had greater mean force while swimming and hence swam faster compared with smaller hatchlings (Burgess et al. 2006), and smaller hatchlings took longer to self-right compared with larger hatchlings (Booth et al. 2013). Thus, nest temperatures also determine the locomotor ability of hatchlings, subsequently influencing their chances of survival.

Hatchlings face a number of threats in their transition from the nest to offshore waters. As hatchlings leave the nest and crawl down the beach, they are vulnerable to depredation and desiccation (Bustard 1972; Janzen et al. 2007). Hatchlings often become inverted while they crawl down the beach and must right themselves to continue moving toward the sea (Hosier et al. 1981; Triessnig et al. 2012). Hatchlings, when inverted, use their head/neck and flippers as levers to lift themselves above the ground and turn over. Neck length along with flipper length could therefore play an important role in determining their self-righting ability (Booth et al. 2013). Additionally, hatchling ability to crawl quickly and right themselves determines the amount of time spent on the beach and exposed to predators. It was observed that green turtle hatchlings that were larger, with a consequently faster swim speed, had a better chance of surviving the swim across the fringing reef at Heron Island on the Great Barrier Reef, Australia (Gyuris 2000). Therefore, high crawl speed, righting ability, and swim speed during their transition from nest to offshore waters are all vital for escaping predators and contributing to hatchling survival (Gyuris 2000).

Rising sand temperatures at nesting beaches around the world pose a serious threat to sea turtle populations of all species (Hawkes et al. 2009). Although there have been numerous studies on the effects of nest temperature on hatchling size and performance, some previous studies used constant incubation temperatures in laboratories to characterize the effect of temperature on hatchling fitness (Hewavisenthi and Parmenter 2001; Booth et al. 2004; Burgess et al. 2006; Fisher et al. 2014; Mueller et al. 2019). Thus, their findings may not reflect the environment of natural nests, which undergo daily fluctuations in incubation temperature. On the other hand, studies conducted in natural field conditions have focused largely on green and loggerhead turtles (Chu et al. 2008; Ischer et al. 2009; Booth and Evans 2011; Read et al. 2012; Wood et al. 2014; Sim et al. 2015; Usategui-Martín et al. 2019; Le Gouvello et al. 2020), and limited studies have been conducted on other species (Maulany et al. 2012; Sim et al. 2014), such as olive ridley turtles. Because the effects of higher nest temperatures on various life history parameters in sea turtles can be highly variable between species and also within populations, it is important to understand the effects on each species, more so at the population level, before formulating appropriate conservation strategies.

In India, olive ridley turtle populations have, in recent years, been subjected to an increased magnitude of threats as a result of anthropogenic activities (Shanker et al. 2004), including the possible effects of climate change. Rising sea level and increasing frequency of storms are additional threats that might affect the nesting and reproductive output of sea turtles (Fuentes et al. 2012). Large-scale fishery-related mortality of olive ridley turtles remains a concern, and rising beach temperatures (Chandarana et al. 2017) can pose a threat to nesting populations through their effects on sex ratios and hatchling survival or fitness.

Hatcheries have been used as a conservation tool in India for decades, starting from the early 1970s, and nests are relocated to hatcheries at many beaches. Over the years, hatchery management practices have been improved to ensure high hatching success and emergence (Phillott and Kale 2017). However, protection of sea turtle eggs in a hatchery addresses largely nonclimatic stressors, such as egg depredation and hatchling mortality and misorientation (Pandav et al. 1998; Karnad et al. 2009; Chandarana et al. 2017). An increase in ambient temperatures could result in high nest temperatures, which would affect hatchling sex ratios, as well as parameters related to hatchling survival, which collectively impact the population. It is therefore important to understand the implications of high nest temperatures on hatchling performance and devise methods to mitigate the impact of temperature.

The current study addresses this knowledge gap and examines the impact of nest temperature on hatchling performance and morphology in the incubation environment of hatcheries. Our main objectives were to examine 1) whether higher nest temperatures lead to smaller hatchlings, in turn leading to reduced locomotor performance, and 2) whether higher nest temperatures affect embryonic development (independent of body size), leading to reduced locomotor performance. In order to determine these, we examined various size (body, flipper, and neck length) and performance (crawl speed and righting ability) parameters for hatchlings at 2 beaches across a range of hatchery temperatures.

METHODS

Study Area. — We carried out the study between December 2018 and May 2019 at hatcheries on 2 nesting beaches on the east coast of India (Fig. 1): Rushikulya in Odisha and Chennai in Tamil Nadu. The 10 × 10-m area hatchery at Rushikulya is at the mouth of the Rushikulya River (19°N, 85°E) toward the south of the 7-km beach. In Chennai, the 15 × 15-m area hatchery is located at Elliot's Beach, Besant Nagar (13°N, 80°E), at the mouth of the Adyar River, which is situated north of the 11-km nesting beach. Since Chennai experiences high ambient temperatures, thick shade cloth is installed over the hatchery from mid-February to the end of May to protect the nests.

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Sporadic, solitary nesting of olive ridley turtles occurs at both locations from December to April, with mass nesting (arribada) also occurring in February or March at the Rushikulya rookery (Pandav et al. 1994). However, turtles nesting at both locations belong to the same population (Shanker et al. 2004), and female turtles nesting in arribadas at Rushikulya are known to participate in solitary nesting as well (Tripathy 2008). During the nesting season of 2018–2019, the arribada did not occur at Rushikulya, and hence all the nests sampled in this study are from solitary nesters.

Typically, clutches of eggs are relocated to a hatchery maintained by the Forest Department at both study sites. During the study, eggs from each nest were collected in a bucket and transported by foot over a short distance (< 5 km) to hatcheries located on the beach, typically within 20–30 min of oviposition. Eggs were reburied in the hatchery within 2 hrs of oviposition, and clutches were incubated at an average nest depth of 32 cm and density of 1 nest/m². We selected 16 clutches in total from these 2 hatcheries for sampling.

Egg Collection and Morphometrics. — Between January and March 2019, 9 clutches from Rushikulya and 7 clutches from Chennai were randomly selected from among those relocated to hatcheries. A sample of 20 eggs were selected from among eggs in the entire clutch by nonsystematic sampling to measure egg diameter using a digital caliper (Mitutoyo; accuracy of 0.01 mm) and weigh using a digital scale (KES; accuracy of 0.01 g). A Hobo 8k pendant temperature data logger (UA-001-08; accuracy of 0.53°C), set to record the temperature every 2 hrs, was placed in the center of each clutch. Nests were labeled using an external cardboard sign with details of clutch size, date and time of relocation, and expected date of hatching (∼ 45 d from date of oviposition).

Nests were monitored when the anticipated date of hatching was close. A basket made of woven leaves was placed on top of each nest to contain hatchlings after emergence and was checked frequently between sunset and sunrise for emerged hatchlings. Incubation period was calculated based on date of oviposition and emergence of hatchlings from the nest. Once approximately 80% of hatchlings emerged from a nest, 20 hatchlings were selected through nonsystematic sampling for measuring morphology and assessing locomotor performance. Afterward, all 20 hatchlings were immediately released near the shore to crawl into the ocean. Data loggers were retrieved from each nest after all hatchlings had emerged. The data loggers were read using HOBOware version 3.7.16 (Onset Computer Corporation), and the average temperature for the incubation period was calculated for each nest.

Hatchling Morphometrics. — For measuring straight carapace length notch to tip, right front flipper total length, and neck length (from where the head scales end to the shoulder), hatchlings were placed on a standard 1 × 1-cm graph sheet, and morphometrics were estimated via digital pictures taken from above. This method avoids potential injury to hatchlings during handling, especially during neck and flipper measurements.

Hatchling Locomotor Performance. — Crawl speed was measured on a racetrack built at 1 corner of the hatchery. Sand was leveled to form a track of 30 × 15 cm that was enclosed on 3 sides with plywood planks and illuminated with dim light (< 500 lux) at the open end to mimic the bright horizon to which hatchlings are attracted (Fig. 2). Hatchlings were placed about 10 cm away from the start line, and the time taken for hatchlings to move from start to finish was recorded. Crawl speed for each hatchling was measured in triplicate, with the track releveled between each individual trial.

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Righting ability was measured on the same track used for crawl speed trials using the procedure of Booth et al. (2013), where hatchlings were inverted (placed on their carapace) and the time required to self-right was recorded. Each hatchling was given 10 sec to self-right. If it failed within this time, the hatchling was returned to its plastron and given a 10-sec rest before another attempt. The self-righting test was continued until the hatchling successfully self-righted 3 times or was given 6 opportunities (successful and unsuccessful) to self-right. Depending on the number of trials taken to self-right, hatchlings were given a righting propensity score from 0 to 6 (Table 1).

Table 1. Righting propensity score designated to hatchlings after self-righting trials (from Booth et al. 2013).

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Statistical Analysis. — Pearson's correlation coefficient was used to explore univariate relationships between hatchling morphology and performance variables. Average nest incubation temperature was used as the predictor variable to measure its relationship with morphometric and performance variables. A Kruskal-Wallis test was used to check for interclutch variations in all parameters and a Mann-Whitney U-test to compare egg and hatchling parameters between both locations. Hatchling data from Rushikulya and Chennai were combined for further analysis, adding location as a variable to distinguish between the 2 sites. Generalized linear models (GLMs) were used to assess the influence of nest temperature on size variables, such as carapace length, flipper length, and neck length, with clutch and location as random factors. Similarly, GLMs were used to measure the effect of hatchling size on locomotor performance and also determine if nest temperature had an effect on hatchling performance with size as a covariate and clutch and location as random variables. All statistical analyses were carried out using the software R (R Core Team) and SPSS version 23.0 (IBM Corporation).

RESULTS

The average nest temperature (mean ± SD) in Rushikulya (30.52°C ± 1.5°C) between January and April 2019 was lower than that of Chennai (33.06°C ± 0.93°C). Nests in Rushikulya experienced a wider average temperature range of 28.26°C–32.83°C than those in Chennai at 31.25°C–34.25°C. As a result, the average incubation period also varied between the 2 sites: 57 d in Rushikulya and 46 d in Chennai (Table 2).

Table 2. Nest temperatures, hatchling size, and performance variables (mean ± SD) observed in Rushikulya and Chennai. Mann-Whitney U-test was carried out to determine the difference between Rushikulya and Chennai for all variables.

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There was significant interclutch variation of egg diameter and weight among clutches at both Rushikulya (p < 0.05) and Chennai (p < 0.05). The egg diameter and weight also varied slightly but significantly (p < 0.05) between the 2 locations (Table 2).

Hatchlings produced from the hatchery in Rushikulya had a significantly greater mean straight carapace length (p < 0.001), flipper length (p < 0.001), and neck length (p < 0.001) than hatchlings from Chennai. However, there was no difference in the weight of hatchlings between the 2 locations (p = 0.85). Both average crawl speed (p < 0.001) and righting propensity (p < 0.001) of hatchlings from Rushikulya were considerably higher than those of Chennai, while average self-righting time of hatchlings was lower (p < 0.001), indicating greater righting ability of hatchlings from Rushikulya hatchery (Table 2). Hatchling weight was correlated with initial egg weight at both locations (r = 0.51, p < 0.05). Hatchling straight carapace length was weakly correlated with egg weight (r = 0.3, p < 0.05) and diameter (r = 0.10, p < 0.05). Similarly, flipper length was also weakly correlated with egg weight (r = 0.3, p < 0.05) and diameter (r = 0.25, p < 0.05).

Effect of Temperature on Hatchling Size. — Hatchling weight was not correlated with nest temperature, and the relationship remained nonsignificant even after accounting for egg weight while using clutch as a random factor (r = –0.22, p = 0.32). The straight carapace length of hatchlings from both hatcheries was negatively correlated with nest temperature (r = –0.79, p < 0.001). A Kruskal-Wallis test showed significant interclutch variation in carapace length (p < 0.001). GLMs showed that nest temperature had a significant effect on carapace length (R² = 0.62, p < 0.001) even with clutch and location as random factors (R² = 0.65, p < 0.001).

Both flipper length and neck length were negatively correlated with nest temperature (r = –0.68, p < 0.001; r = –0.68, p < 0.001). There was significant interclutch variation in both flipper length and neck length (p < 0.001). Nest temperature had a significant effect on flipper length and neck length (GLM R² = 0.47, p < 0.001, and R² = 0.47, p < 0.001, respectively), which persisted even after accounting for clutch and location as random factors (GLM R² = 0.59, p < 0.001, and R² = 0.49, p < 0.001, respectively).

Effect of Hatchling Size on Locomotor Performance. — All the morphometric variables, that is, straight carapace length, flipper length, and neck length, had high positive correlations with crawl speed and righting propensity score and a strong negative correlation with self-righting time (Table 3).

Table 3. Matrix of correlation coefficients (r) for hatchling size and locomotor performance variables.

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All size variables were strongly correlated with each other, and therefore any of the size variables could be used as a representative of other variables. Thus, straight carapace length was used as the proxy variable for representing all size variables. GLM analyses showed that hatchling size had a significant effect on hatchling crawl speed (R² = 0.57, p < 0.001), righting ability (R² = 0.43, p < 0.001) (Fig. 3), and righting propensity score (R² = 0.35, p < 0.001), which remained significant after including clutch and location as random factors (R² = 0.72, p < 0.001; R² = 0.64, p < 0.001, and R² = 0.55, p < 0.001, respectively).

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Effect of Temperature on Locomotor Performance. — Crawl speed had a strong negative correlation with nest temperature (r = –0.83, p < 0.001). Because straight carapace length was chosen as the proxy size variable and also had a strong correlation with crawl speed, GLMs were used to examine the influence of nest incubation temperature on crawl speed while controlling for the effect of carapace length by treating it as a covariate. Nest temperature had a significant effect on crawl speed even after accounting for carapace length, clutch, and location (R² = 0.76, p < 0.001).

The time taken for hatchlings to self-right increased with nest temperature (r = 0.76, p < 0.001). Nest temperature had a significant effect on righting ability regardless of hatchling size; the relationship remained significant after accounting for clutch and location as well (GLM R² = 0.63, p < 0.001).

Righting propensity score was negatively correlated with nest temperature (r = –0.66, p < 0.001). Nest temperature had a significant effect on the righting propensity score even after controlling for hatchling size (GLM R² = 0.45, p < 0.001), and the effect remained significant even after accounting for clutch and location (GLM R² = 0.53, p < 0.001).

DISCUSSION

As ambient temperatures and consequently sand temperatures around the world increase as a result of climate change, sea turtles will be subjected to an increased number of threats. Increased female bias in sex ratios, as a result of growing temperatures, poses a significant threat to global populations of sea turtles (Chu et al. 2008; Jensen et al. 2018). Higher temperatures are also known to influence hatchling morphology and performance, which could further aggravate the threat by potentially influencing hatchling recruitment and survival. Hence, it is important to understand the influence of temperature on sea turtle hatchling development, which could possibly lead to demographic changes in the populations. This is especially important in the context of modified temperature regimes that occur in hatcheries, which are a common conservation tool for sea turtles around the world. In our study in hatcheries on the east coast of India, we found that higher nest temperatures resulted in smaller hatchlings and also weaker locomotor ability through slower crawl speed and poorer righting ability. This would make hatchlings more vulnerable by increasing their exposure to predators.

Comparison of Rushikulya and Chennai. — The average nest temperatures varied significantly between hatcheries at the 2 rookeries. The hatchery in Rushikulya to the north experienced a wide temperature range compared with Chennai, where the lowest average temperature experienced by nests in Rushikulya (28.26°C) was far below the lowest average temperature experienced by nests in Chennai (31.25°C). Clutches in the hatchery at Chennai experienced higher nest temperatures with a narrower temperature range throughout the season, which could be attributed to the shading of the hatchery from late February to protect eggs against extremely high temperatures. Nest temperatures remained as high as 32°C–34°C in the Chennai hatchery throughout the season, even after shading from mid-February.

Sea turtle embryos are resistant to extreme high temperatures during the last phase of embryonic development, when the nest temperatures usually increase as a result of metabolic heat produced from the late-stage embryos (Maulany et al. 2012; Howard et al. 2014). However, extreme high nest temperatures that persist throughout the incubation period, as was the case with nests in Chennai, could potentially have drastic impacts on embryonic development and hatchling fitness.

Egg weight and diameter showed significant interclutch variation at both Chennai and Rushikulya and also varied between the 2 locations. Hatchling weight was correlated with egg weight but not nest temperature. This finding is consistent with earlier studies investigating hatchling weight and incubation temperature (Reece et al. 2002; Ischer et al. 2009) and is potentially explained by the influence of maternal factors, such as egg weight (Glen et al. 2003; Ozdemir et al. 2007; Booth et al. 2013), where larger egg weight resulted in larger hatchlings due to the presence of more available yolk material, which governed the amount of tissue formed and subsequently hatchling size (Wallace et al. 2006).

Hatchlings from Rushikulya were relatively larger with longer carapace, flipper, and neck lengths compared with hatchlings from Chennai (Fig. 4A). This could be attributed largely to site-specific variations, especially nest temperatures, that lead to high variability in the length of the incubation period experienced by the nests in Chennai and Rushikulya.

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Effect of Temperature on Hatchling Size. — The strong negative correlation between hatchling size variables and nest temperature suggests that warmer temperatures lead to reduced hatchling size by reducing the duration of the incubation period. This finding is consistent with earlier studies (Booth and Astill 2001; Hewavisenthi and Parmenter 2001; Reece et al. 2002; Ischer et al. 2009; Maulany et al. 2012; Read et al. 2012; Booth et al. 2013; Wood et al. 2014).

Variation in hatchling size variables with nest temperature could be a manifestation of the incubation period. Hatchlings from nests with a lower mean nest temperature experienced longer incubation periods (60–70 d) compared with nests with a higher nest temperature (45–46 d). A longer incubation period likely allowed more yolk to be converted into hatchling tissue, thus resulting in larger hatchlings (Reece et al. 2002; Burgess et al. 2006; Ischer et al. 2009; Staines et al. 2018). Size has potential implications for hatchling survival, depending on the posthatch environment. Cavallo et al. (2015) used modeling to predict the implications of hatchling locomotor ability on their dispersal and predicted weaker dispersal and survival of smaller hatchlings even after accounting for high energy reserves in smaller hatchlings and their ability to survive longer starvation periods compared with larger hatchlings (Staines et al. 2018).

Effect of Hatchling Size on Locomotor Performance. — All hatchling size variables were strongly correlated with crawl speed, self-righting time, and righting propensity score. Temperature-induced changes in hatchling size seemed to have had a significant effect on hatchling locomotor performance, implying that nest temperature affects not only the size of hatchlings but also, consequently, their locomotor ability. Larger hatchlings had faster crawl speeds and took less time to right themselves when overturned. Therefore, smaller hatchlings emerging from warmer nests would take longer to crawl down the beach or right themselves when inverted after crawling over beach debris or washed ashore by waves, thus increasing their exposure time to terrestrial predators in their transition from nest to sea.

Righting propensity score was an indication of the technique used by hatchlings to self-right (Booth et al. 2013). As soon as hatchlings were placed on their carapaces, they began to beat their fore and hind flippers against the surface to right themselves. However, they could successfully self-right only when they stretched and rotated their necks to press the dorsal surfaces against the ground, allowing hatchlings enough leverage to flip over. Booth et al. (2013) also observed that the movement of the heads and necks of hatchlings, not hatchling flippers, aids in self-righting. Additionally, we found that neck length, among other size variables, had the highest correlation with hatchling self-righting ability and righting propensity score (Table 3), validating its importance for the hatchling to quickly and successfully self-right.

Effect of Temperature on Locomotor Performance. — Hatchling crawl speed varied significantly between Rushikulya and Chennai. Chennai hatchlings, produced from nests of higher nest temperature, were slower than hatchlings from Rushikulya (Fig. 4B). This is consistent with studies that showed that higher incubation temperatures were associated with reduced crawl speed, righting ability, and swimming performance (Booth et al. 2004, 2013; Burgess et al. 2006; Ischer et al. 2009; Maulany et al. 2012; Read et al. 2012; Sim et al. 2015). Although the reduced crawl speed and righting ability observed in hatchlings at Chennai compared with Rushikulya could be a result of the smaller hatchling size, it was also found that nest temperature influenced the crawl speed and righting ability independent of hatchling size. This indicates that while high nest temperature results in reduced hatchling size, which has implications for the performance of the hatchling, nest temperature also has a direct influence on hatchling performance.

Exposure to extreme temperatures during the incubation period is thought to influence the developing embryonic physiological systems, resulting in poor hatchling terrestrial locomotor performance (Ischer et al. 2009; Maulany et al. 2012). While the mechanism by which temperature could directly influence hatchling performance remains largely unknown, it is hypothesized that higher temperatures could be affecting the muscle structure and the frequency of fiber types in the locomotor skeletal muscles (Booth 2017). Varying incubation temperatures were found to affect the frequency of the fiber types that make up the muscle physiology, affecting the swim performance of juvenile fish (Booth 2017). However, this has not been tested in sea turtle hatchlings so far and is a potential area of future research.

Inexplicably, hatchlings produced from a few nests in Chennai that experienced almost the same incubation temperature as those in Rushikulya showed significantly reduced crawl speed and righting ability. This could be a result of variations in factors at the local level at both rookeries, such as maternal influence and differences in other nest environment factors, such as soil characteristics and moisture. Similar differences in hatchling size and performance were found between loggerhead hatchlings from Mon Repos, Australia, and La Roche Percée, New Caledonia (Read et al. 2012) and flatback turtle hatchlings from Mon Repos and Bare Sand Island rookeries in Australia (Sim et al. 2014).

Reduced locomotor performance may increase hatchling exposure to terrestrial predators, such as dogs, crabs, and birds (Maulany et al. 2012). This might not have a severe impact on the mortality rate of hatchlings produced from hatcheries in India, as they are usually released closer to the water and guarded by staff or volunteers as they crawl down the beach. However, once hatchlings enter the water, they are vulnerable to numerous predators as they proceed to offshore waters. Hatchlings that are smaller in size and have poor locomotor abilities might be at a disadvantage compared with larger hatchlings due to their failure to escape gape-limited predators in the ocean (Gyuris 2000). Olive ridley hatchlings produced at both extremely low (< 28°C) and high (> 32°C) incubation temperatures were found to be small and had poor swimming performance compared to hatchlings produced at intermediate temperatures (28°C–30°C) (Mueller et al. 2019). Therefore, small hatchling size and poor locomotor ability, as a result of extreme incubation temperatures, could influence the survival of hatchlings in the predator-rich inshore waters (Gyuris 2000).

In summary, the lower terrestrial locomotor performance of hatchlings produced as a result of higher nest temperatures could potentially reduce hatchling recruitment to the population. Even with high hatching and emergence success, if hatchlings that are produced perform poorly, the survival rate would invariably be low, thus not serving the purpose of long-term conservation through hatcheries. As global temperatures continue to increase as a result of climate change, taxa such as sea turtles, which have long generation times, will find it difficult to adapt their nesting behavior (Staines et al. 2018). The detrimental effects of increasing temperatures on hatchlings can be reduced by adopting hatchery management practices that incorporate site-specific needs and that also address climate-related issues.

Shading and watering of hatcheries was found to be an effective measure in reducing the temperature inside the hatchery (Maulany et al. 2012; Wood et al. 2014; Hill et al. 2015). Apart from rising sand temperatures across the beach, crowding of nests inside the hatchery, where the nest density is higher than the recommended 1 nest/m², can result in increased nest temperatures (Mortimer 1999; Shanker et al. 2003; Patino-Martinez et al. 2012). Increasing the spacing between the nests could possibly help in reducing nest temperatures. Hatchery management practices need to be regularly assessed and adjusted to adapt to the changing climatic conditions based on environmental data. Reducing the sand temperatures in hatcheries could improve hatchling quality, thus increasing their likelihood of survival and subsequently contributing to recruitment of hatchlings into the adult population. This could play an important role in the demography of turtles in the region. Therefore, if further studies suggest that reduced nest temperatures would improve hatchling performance, shading of hatcheries or in situ nests may be considered an option. However, it is important to assess the effectiveness of different degrees and the extent of shading before the practice is incorporated into hatchery management practices. Because the temperature regimes vary at the local level, shading practices must be adjusted to meet site-specific requirements.