Introduction

Kemp’s ridley (Lepidochelys kempii Garman, 1880) is the most critically endangered sea turtle species in the world. Nearly all nesting by this species is along shores of the western Gulf of Mexico (GoM), from Texas,

USA, to Veracruz, Mexico (NMFS and USFWS, 2015). This region is the documented historic nesting range of the species and marks the smallest geographic nesting range for any sea turtle species (Pritchard and Márquez-M., 1973). The largest concentration of nesting occurs near the village of Rancho Nuevo, in Tamaulipas, Mexico, where an estimated 26,916 Kemp’s ridley turtles were filmed nesting on a 321 m section of beach during a four-hour period in June of 1947 (Bevan et al., 2016) in a synchronous nesting emergence called an arribada. In the early 1960s, biologists described a severe decline in nesting (Hildebrand, 1963), and thus began species recovery efforts at the main nesting beach

Herpetology Notes, volume 13: 907-923 (2020) (published online on 16 November 2020)

Threats to Kemp’s ridley sea turtle (Lepidochelys kempii Garman, 1880) nests incubating in situ on the Texas coast

Donna J. Shaver1,*, Hilary R. Frandsen1, J. Shelby Walker1, Jeffrey A. George2, and Christian Gredzens1

1 National Park Service, Padre Island National Seashore, Corpus Christi, TX 78480, USA.

2 Sea Turtle, Inc., South Padre Island, TX 78597, USA.* Corresponding author. E-mail: donna_shaver@nps.gov

Abstract. We identified threats to, and quantified success of, in situ nests of the Kemp’s ridley sea turtle (Lepidochelys kempii). Kemp’s ridley is the most critically endangered sea turtle species worldwide and efforts have been underway for more than 40 years to help recover the species, including the facilitation of forming a secondary nesting colony in south Texas, USA, as a safeguard against extinction. Typically, Kemp’s ridley nests located in Texas are relocated after egg laying for protected incubation in fenced corrals or a laboratory incubation facility; these management practices protect clutches and hatchlings from many threats that affect in situ nests. This study examined records for 78 Kemp’s ridley sea turtle nests discovered in situ (i.e., not relocated for incubation in a fenced corral or a laboratory incubation facility) in Texas between 1980–2018. Of the 78 in situ nests, 15 (19.2%) were completely predated and thus no hatchlings emerged, 29 (37.2%) emerged observed, 33 (42.3%) emerged unobserved, and one (1.3%) was excavated after incomplete predation. Observed nest emergences occurred primarily between 0600 h and 1000 h. Fifty (64.1%) in situ nests were disturbed by predators and/or humans before or after emergence. Site disturbance and limited observation of emergence prohibited accurate accounting of the number of hatchlings that successfully entered the Gulf of Mexico (GoM) from these nests. We documented 237 hatchlings that died on the beach due to vehicle drive-over (n = 42), predation (n = 131), overheating and desiccation (n = 54), disorientation (n = 1), and unknown cause (n = 9). Human intervention limited hatchling mortality at several of these nests. Mean estimated maximum hatchling emergence success was 63.2%, but actual success was likely much lower because additional mortality probably occurred but went undocumented due to site disturbance. Additionally, from 2005–2007, a total of 155 Kemp’s ridley nest sites at Padre Island National Seashore (Padre Island NS) were marked after eggs were removed for protected incubation and monitored for impacts from five threat types (tidal inundation, predator interaction, human tampering, vehicle drive-over, and plant root penetration). Ninety-nine percent of sites (154 of 155) were impacted by at least one threat during the study period. Generalised linear models were used to describe the prevalence of the three most common threats (presences or absences of ghost crab burrows, coyote tracks, and tidal inundation) and the cumulative number of threats at sites grouped along four beachfront sections, describing variation in threats by section and year. Results of these two studies illustrate that, since in situ nests on the Texas coast face significant threats and yield fewer hatchlings than relocated nests, relocation of Kemp’s ridley clutches for protected incubation must be continued for this critically endangered species.

Keywords. maximum emergence success, in situ incubation, tidal inundation, nest predation, Gulf of Mexico, nest relocation, Kemp’s ridley, sea turtle

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at Rancho Nuevo (Márquez-M. et al., 2005; NMFS et al., 2011). Fearing extirpation of the species, the USA joined these efforts and supported the on-going bi-national recovery program, part of which includes the formation of a secondary nesting colony of Kemp’s ridleys at Padre Island National Seashore (Padre Island NS), on North Padre Island, Texas, USA, as a safeguard against species extinction (Shaver and Caillouet, 1998; 2015; Shaver, 2005; Caillouet et al., 2015). The goal of this effort is to provide a safe-haven for Kemp’s ridley nesting in the event of a natural or human-caused disaster near the main nesting beach. Padre Island NS is within the historical range of the Kemp’s ridley (Werler, 1951; Carr, 1963; Hildebrand, 1963) and preserves the longest stretch of undeveloped barrier island beach in the USA (Weise and White, 1980).

After decades of conservation, nesting has increased on the western GoM coast, including at Padre Island NS, where a secondary nesting colony is becoming established. Today, Texas is the only USA state where sea turtle nesting is predominated by the Kemp’s ridley turtle and more Kemp’s ridley nests are found at Padre Island NS than at all other USA locations combined (Shaver et al., 2016). Based on tag returns and satellite tracking, nesting females exhibit beach fidelity, returning to the same or nearby nesting beaches approximately 95% of the time (Shaver, 2005; Shaver and Caillouet, 2015; Gredzens and Shaver, 2020).

Future recovery of this species is currently unclear. Since 2010, yearly documented numbers of nests deviated unexpectedly from exponential increases documented in previous years and have not only not returned to this trend, but some years have had sharp declines in nesting (Shaver and Caillouet, 2015; Wibbels and Bevan, 2016). Sustained success of the secondary nesting colony at Padre Island NS depends on continued U.S. Endangered Species Act protections (Valdivia et al., 2019) of nesting turtles, eggs, and hatchlings, and continued recruitment to this colony. To achieve this success, conservation programs must be firmly based on studies of how and to what extent factors, many of which may be specific to a region, jeopardise a species’ survival (Liles et al., 2015; brego et al., 2020). Consequently, conservation). and management strategies should be evidence-based, tailored to the local habitat, and species-specific (Liles et al., 2015; Murphy and Weiland, 2016; Ceriani et al., 2019; Ábrego et al., 2020).

For decades, Kemp’s ridley recovery efforts have involved translocating eggs from virtually all nests found in Mexico and Texas to hatcheries to prevent loss

due to predation, poaching, tropical storms, inundation by high tides, and public vehicle use (Guzmán-Hernández et al., 2007; NMFS et al., 2011; Shaver and Caillouet, 2015; Shaver et al., 2016). Specifically, threats to Kemp’s ridley nests documented on Texas beaches (summarised in Table 1) include environmental factors such as predators, elevated temperatures, beach characteristics (e.g., topography and vegetation), marine debris, and tidal fluctuations alongside anthropogenic factors such as camping activities, poaching, and beach driving. Both environmental and anthropogenic factors result in multiple stressors that should be considered in the management of Kemp’s ridley nesting beaches to prevent extinction of this critically imperilled species.

Continued protected incubation of clutches has helped restore the Kemp’s ridley population (Caillouet et al., 2016), yet some argue against nest relocation as a sea turtle conservation measure. Nest relocation is controversial, as sea turtle conservationists continue to weigh the potential risks of possible reduction in hatchling fitness or sex-ratio alteration (Limpus et al., 1979; Godfrey and Mrosovsky, 1999; Mortimer, 1999) against the benefit of increasing hatchling production to restore populations of threatened and engangered species (Dutton et al., 2005; Mazaris et al., 2005). However, it is well established that protected incubation, combined with new state and federal fisheries regulations such as the requirement of turtle excluder devices (TEDs) in shrimp trawling, led to the observed exponential increase in Kemp’s ridley nesting from the mid-1980s to 2009 (Caillouet, 2014). Translocated Kemp’s ridley clutches in hatcheries at Padre Island NS have a 12.5–32.5% increased success rate over in situ clutches laid at Rancho Nuevo and a 13% higher survival rate of hatchlings on the beach during release (Bevan et al., 2014; Shaver et al., 2016). In addition, relocation to hatcheries (García et al., 2003; Martínez et al., 2007; Clusella Trullas and Paladino, 2007; Patino-Martinez et al., 2012a; Hart et al., 2016; 2018; Liles et al., 2019), artificial incubation (Raj, 1976; Hart et al., 2014; 2016; 2018), short-distance relocation (Eckert and Eckert, 1990; Pfaller et al., 2009; Pintus et al., 2009; Tuttle and Rostal, 2010; Dellert et al., 2014), delayed translocation (Abella et al., 2007; Ahles and Milton, 2016), and hypoxic translocation (Williamson et al., 2017) of clutches have been successfully used in recovery efforts for other sea turtle species, including green (Chelonia mydas), hawksbill (Eretmochelys imbricata), leatherback (Dermochelys coriacea), loggerhead (Caretta caretta), and olive ridley (Lepidochelys olivacea) turtles.

To evaluate the protection measures for Kemp’s ridley nests in Texas, the emergence success of Kemp’s ridley clutches incubated in situ versus those protected in a laboratory incubation facility (i.e., temperature controlled indoor facility where eggs are incubated in polystyrene boxes filled with sand from the nesting beach) or corral (i.e., fenced and enclosed section of protected beach above the high tide line) was documented. Further, we identified the observed emergence period and causes of hatchling mortality of in situ nests. We also monitored marked nest sites after egg removal to document presence and cumulative number of common threats at Padre Island NS, vital for informing nest management activities, and a crucial component of recovery efforts for this critically endangered species.

Materials and Methods

Patrols and nest detection.—From 1980–2018, biologists attempted to locate a nest at each site where a nesting Kemp’s ridley turtle or tracks were reported on the Texas coast (Shaver and Caillouet, 2015). Nest detection was opportunistic until systematic patrols

began at Padre Island NS in 1986, however, coverage was sporadic, until repeated daily patrols began in 1998 (Shaver, 2005; Shaver et al., 2016). As Kemp’s ridley nesting increased and spread geographically on the Texas coast (Shaver, 2005; Shaver et al., 2016), nest detection patrols expanded to other areas in Texas (NMFS et al., 2011). Patrols have been conducted in most areas of the state from April to mid-July each year since 2005. These patrols have been conducted daily from Mustang Island southward to the USA-Mexico border, but only conducted 2–6 days per week from San Jose Island northward to the Texas-Louisiana border (Fig. 1). Nests were also located in response to reports from the public. Located nests were documented, clutches were excavated and relocated to a laboratory incubation facility or corral for protection, eggs were monitored for hatching and emergence, and hatchlings were protected during release (Shaver and Caillouet, 2015; Shaver et al., 2016).

In situ nests.—Unprotected nests that incubated in situ were designated as being at either known or unknown sites. Known sites were locations where a

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Table 1. Anthropogenic and natural threats* that affect Kemp’s ridley sea turtle (Lepidochelys kempii) adults (nesting), hatchlings, and nests (embryonic) on Texas, USA, beaches. *Natural threats can be influenced indirectly by anthropogenic impacts.

nesting turtle or tracks were observed, but eggs could not be found. These sites were marked and monitored for signs of predation or hatching through the projected incubation period. Unknown sites were locations where a turtle nested unobserved, and the site was not detected until biologists or the public found evidence of nest predation or hatching. When possible, each in situ nest was excavated to document clutch size and maximum emergence success (see data analysis). Emergence times were reported by visitors recreating on the beach and by biologists during nest detection patrols, who witnessed hatchlings emerging from in situ nest sites.

Marked nest sites.—To further study threats to in situ nests without risking loss of endangered Kemp’s ridley eggs, from 2005–2007, we marked 155 Kemp’s ridley egg chambers located at Padre Island NS by placing four Carsonite® Curv-Flex® delineators (Carsonite Composites, Newberry, South Carolina, USA) to form

a one m2 plot, after eggs were removed from these sites. This included 25 marked sites during 2005, 60 during 2006, and 70 during 2007. Each was assigned a site number and delineators were marked with a sign displaying “do not disturb, sea turtle study area” and reflective tape. We checked sites once daily and recorded any disturbance to the delineators or within the one m2 area from tidal inundation, predator interaction, human tampering, vehicle drive-over, and plant root penetration (i.e., deep roots of native coastal prairie vegetation). After a site visit, we erased any signs of disturbance to ensure events were not recorded twice by observers. Predator signs included for this analysis were ghost crab (Ocypode quadrata) burrows, and coyote (Canis latrans), raccoon (Procyon lotor), and gray fox (Urocyon cinereoargenteus) tracks. We removed delineators from the study site after the clutch hatched in protected incubation, or during hurricane preparations in 2005 and 2007 to prevent loss of equipment. In cases when a clutch did not hatch, we removed study markers at 60 days. The monitoring ended prior to the end of the incubation period for 38 sites, including eight where delineators were washed away by tides, two where beach visitors removed the delineators, and 28 where delineators were removed for hurricane preparations.

Data Analysis.—For in situ nests, clutch size was estimated from observed hatchlings, eggshells, and unhatched eggs in nest chambers located intact (n = 46). When the nest chamber could not be located or the site had been disturbed by predators or people and eggs and/or eggshells were known or suspected to be missing (n = 32), a clutch size of 97 eggs was assumed, based on the mean clutch size for Kemp’s ridley nests in Texas (Shaver and Caillouet 2015; Shaver et al., 2016).

The maximum emergence success was estimated by dividing the number of hatchlings that both emerged from the nest naturally as well those that were rescued live from the egg chamber, and those removed by predators or human disturbance/tampering, by the estimated total number of eggs. This estimated total number of eggs includes the 32 nests that were assigned a proxy clutch size of 97 eggs. This calculation differs from the traditionally used “emergence success” (Miller, 1999) with the inclusion of live hatchlings rescued or facilitated from the egg chamber. This was necessary since nests found in situ were often documented in a disturbed state where predators or human activities facilitated removal of live hatchlings from the egg chamber prior to the arrival of biologists. This method of calculation also enables direct comparison of relocated clutches to

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Figure 1. Geographic areas where Kemp’s ridley sea turtle (Lepidochelys kempii) nests were found along the Texas, USA, coast from 1980–2018. Inset (A) shows regions and extent of the marked nest site study at Padre Island National Seashore (NS) from 2005–2007.

in situ clutches. Mean maximum emergence success was calculated similarly for all relocated clutches and reported for comparison. A chi-square test was also used to determine if the frequencies of clutches found in situ versus protected were independent of major Texas coastal areas (San Jose Island to the Texas-Louisiana border vs Mustang Island to the USA-Mexico border), which have different levels of patrol effort (variable vs 7-days/week).

Threats were evaluated using generalised linear models (GLMs) to predict threat prevalence (proportion of days a threat was recorded) and intensity (cumulative number of unique threats) at each of the 155 marked nest sites at Padre Island NS. Threat prevalence was modelled as the number of “successes” (threat presence) and the number of “failures” (threat absence) at each nest site during the study period using a quasibinomial distribution with logit link. Response variables were (in order of highest prevalence) ghost crab burrows, coyote tracks, and tidal inundation. Five additional threats were observed, but not modelled for prevalence due to low occurrence, including human tampering (n = 75), plant root penetration (n = 37), vehicle drive-over (n = 25), raccoon tracks (n = 11), and fox tracks (n = 1), during the 5,537 individual site checks. Threat intensity was modelled as the cumulative number of unique threats (0–8) recorded at each nest site during the study period using a quasipoisson distribution with log link and weighted by the sampling intensity at each site (i.e., number of days). All response variables were modelled as functions of the fixed main covariates year (2005–2007) and region (North, North Central, South Central, and South), which represented four equal length (26.3 km) GoM beachfront sections at Padre Island NS (Fig. 1). Quasi-type distributions were used for all models due to the presence of overdispersion in the datasets. Preliminary data exploration was carried out following recommended protocols and model fits were evaluated using standard methods (Zuur et al., 2010). All statistical analyses were conducted in R version 3.6.3 (R Core Team, 2020). Results are presented as the mean ± one standard error (SE).

Results

In situ nests.—From 1980–2018, we documented a total of 2,614 Kemp’s ridley nests in Texas, with 11.1% located in north Texas (Texas-Louisiana border to San Jose Island) and 88.9% located in south Texas (Mustang Island to the USA-Mexico border) (Table 2). Of the 2,614 documented nests, 2,536 were protected and 78

incubated in situ (Table 2). The frequency of in situ nests on north Texas beaches (5.9%) was higher than those on south Texas beaches (2.6%) (χ2 = 8.249, p < 0.01) which have higher levels of patrol effort. In situ nest sites included 38 known to biologists at the time of egg laying and 40 that were unknown to biologists until the nests were found predated or hatched.

Of the 78 in situ nest sites, 15 were completely predated, 29 emerged observed, 33 emerged unobserved, and one was excavated after incomplete predation and hatchlings were released. Twenty-five of the 29 observed emergences (86.2%) occurred between 0600 h and 1000 h, with the remaining four emergences observed at other times during the day and night (Fig. 2). Fifty (64.1%) in situ nest sites were disturbed by predators or humans before, during, or after hatching. Forty of the disturbed nests were impacted by predators (coyotes, badgers [Taxidea taxus], raccoons, hogs [Sus scrofa], ants [Solenopsis sp.], ghost crabs), seven by human activities (trampling, beach driving, beach maintenance, digging by hand), and three by both predator and human activities.

Nest disturbance and lack of observation of emergence prohibited accurate quantification of the number of hatchlings that emerged and successfully entered the GoM surf from the 78 in situ nests. From 1980–2018, we recorded 237 hatchlings that had been killed at 18 of these sites. Forty-two hatchlings were killed from vehicle crushing (seven nests), 54 from heat and desiccation (two nests), 103 from ants (three nests), 28 from other predators including crabs, coyotes, raccoons, and badgers (three nests), one due to disorientation (one nest), and nine from unknown reasons (five nests). Biologists occasionally arrived at in situ nest sites as hatchlings were emerging from the nest or crawling

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Figure 2. Observed emergence times of in situ Kemp’s ridley sea turtle (Lepidochelys kempii) nests found along the Texas, USA, coast from 1980–2018.

down the beach, and then protected those hatchlings until they entered the surf. Estimated mean maximum emergence success for in situ nests was 63.2 ± 5.4%. For comparison, mean emergence success for clutches relocated for protected incubation was 84.0 ± 0.7% (1980–2018; 2,536 clutches).

Marked nest sites.— One hundred and fifty-four of the 155 marked nest sites were impacted by at least one threat during the study period. From a total of 5,537 daily site checks, we recorded 1,781 predator visits, 183 tidal inundations, 75 incidents of human tampering (e.g., removal of delineators, tents staked to the delineators, trash placed within the marked site), 37 observations of plant root penetration, and 25 vehicle drive-overs. Overall, marked nest sites were exposed to 2.5 ± 0.1 unique threats during the 3-year study. Ghost crab burrows were the most frequent threat documented in any year and were documented at 27.9% of site checks (Table 3). Coyote tracks were documented at 4.1% and

tidal inundation was observed at 3.3% of site checks. Evidence of vehicle drive-over was seen at 0.5%, plant root penetration was noted at 0.7%, and raccoon tracks were documented at 0.2% of site checks. With regard to individual sites, ghost crab burrows were documented at 96.8% (150 of 155 sites) with more sites being impacted in 2006, coyote tracks were documented at 56.8% (88 of 155) with more sites impacted in 2005, and tidal inundation was documented at 40.0% of sites (62 of 155) with more sites impacted in 2005 (Table 4).

GLMs indicated the prevalence of ghost crab burrows and coyote tracks at individual sites were lowest in the North Central region of Padre Island NS (ghost crab, 18.2 ± 5.9%, p < 0.001; coyote, 2.6 ± 2.4%, p < 0.05) (Fig. 3, Table 5). Overall prevalence of ghost crab burrows and coyote tracks were highest in the North region (ghost crab: 37.2 ± 10.1%; coyote: 6.2 ± 5.0%), but not significantly different than the South Central and South regions (ghost crab, 30.1 ± 6.2%, p = 0.056 [South Central], 30.5 ± 7.8%, p = 0.062 [South]; coyote,

Table 2. Total number of Kemp’s ridley sea turtle (Lepidochelys kempii) nests ordered by location in Texas, USA, from north to south, and number recorded in situ, from 1980–2018. Known = the number of nests that were located at sites where a nesting female or her tracks were recorded at egg laying; Unknown = the number of nests that were located at sites where a nesting female or her tracks were not recorded at egg laying.

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4.5 ± 2.8%, p = 0.336 [South Central], 3.7 ± 3.2%, p = 0.434 [South]) (Fig. 3, Table 5). Prevalence of ghost crab burrows increased during the study period (2006, p < 0.05; 2007, p < 0.001), while coyote tracks decreased (2006, p < 0.001; 2007, p < 0.001) (Fig. 3, Table 5). Tidal inundation prevalence did not significantly differ across regions (1.5 ± 2.1%–5.0 ± 3.3%), but was highest in the North Central (5.0 ± 3.3%, p = 0.247), and was highly variable between years (1.9 ± 1.8%–8.0 ± 5.4%), but lowest in 2006 (1.9 ± 1.8%, p < 0.01) (Fig. 3, Table 5). Threat intensity was highest in the North (3.1 ± 0.2) and decreased in more southern regions, but only

significantly in the South Central region (2.4 ± 0.1; p < 0.05) (Fig. 4, Table 5). The number of cumulative threats observed also decreased over time, with significantly lower threat intensity in 2006 (2.5 ± 0.1; p < 0.001) and 2007 (2.1 ± 0.1; p < 0.001) (Fig. 4, Table 5).

Discussion

This is the first study to document and quantify specific threats to Kemp’s ridley sea turtle clutches incubating in situ on the Texas coast, USA. We documented that the mean maximum emergence success of Kemp’s ridley hatchlings was more than 20% higher for eggs protected

Table 3. Yearly prevalence for the three most frequently documented threat types in each of the four sections of Padre Island National Seashore, Texas, USA (North, North Central, South Central, South), and totals for nest site checks documented in 2005, 2006, and 2007 at Kemp’s ridley sea turtle (Lepidochelys kempii) nest sites after eggs were removed. Crab = ghost crab (Ocypode quadrata) burrows; Coyote = Canis latrans tracks; Water = tidal inundation, n = total number of site checks; %: percent of site checks where threats were documented.

Table 4. Percent of Kemp’s ridley sea turtle (Lepidochelys kempii) nest study sites where threats were documented at Padre Island National Seashore, Texas, USA, in 2005, 2006, and 2007 after eggs were removed. Ghost crab (Ocypode quadrata) burrows; Coyote (Canis latrans) tracks; Raccoon (Procyon lotor) tracks; N = total number of study sites; %: percent of individual sites where threat was documented at least once.

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in hatcheries (84.0%) than was the mean estimated maximum success for eggs incubated in situ (63.2%). This estimated mean maximum emergence success of in situ clutches is likely greatly inflated as additional undocumented mortality from predators and human interaction likely occurred in these nests and on the beach prior to arrival of biologists. In the marked site study at Padre Island NS all but one site were impacted by threats, further illustrating that it is highly likely that clutches left in situ could be harmed during incubation by one or more of the threat factors documented.

Nest site disturbance may have been more prevalent than documented, as predator tracks and signs of human

activity may have been blown away by wind or washed away by high tides or heavy rain before they were examined. Threats varied significantly between years as was expected since yearly differences in weather and other factors influence these threats. Tidal inundation had very high variability within the regions as some sites were repeatedly flooded and others were never flooded, with higher overall rates during 2005 and 2007 when hurricanes were recorded near the Texas coast. These results indicate that the presence of large storm systems may elevate the threat of nest inundation, especially along the south Texas coast. Specifically, the Central North region of Padre Island NS had the largest prevalence of tidal inundations, though not significantly. This region of the island, as well as parts of the South Central, is characterised by narrower, steeper beaches and both are hotspots for Kemp’s ridley nesting activity in Texas (Culver et al., 2020). Increased inundation frequency in the North Central region may relate to the observed lower frequencies of predator visits at marked nest sites in the area (i.e., by washing away evidence of visits), however, other factors such as physical beach characteristics (e.g., sand grain size/type, dune height), habitat quality (e.g., prey availability, vegetation), or level of anthropogenic activity may have also played a role in the lower prevalence of predator visits.

The North section of Padre Island NS has more frequent recreational visitation than the other three regions and nest sites in this area had higher cumulative numbers and increased prevalence of threats. Ghost crab burrows

Figure 3. Generalised linear model predictions for the prevalence of the three most common threat types to in situ Kemp’s ridley sea turtle (Lepidochelys kempii) nests: (A) ghost crab (Ocypode quadrata) burrows, (B) coyote (Canis latrans) tracks, and (C) tidal inundation among four regions (North, North Central, South Central, South) at Padre Island National Seashore, Texas, USA. Error bars represent one standard error of the mean.

Figure 4. Generalised linear model predictions for the intensity of threats to in situ Kemp’s ridley sea turtle (Lepidochelys kempii) nests among four regions (North, North Central, South Central, South) at Padre Island National Seashore, Texas, USA. Error bars represent one standard error of the mean.

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and coyote tracks were also more prevalent in the North, likely due to increased food resource availability from scavenging of vacated camp sites and discarded food scraps from visitors alongside habituation to human presence. For example, previous studies have shown higher densities of coyotes and loss of fear of humans

in more humanised areas (Baker and Timm, 1998; Fedriani et al. 2001). Increases in ghost crab densities and body conditions have also been recorded near areas of increased human use (e.g., campsites) (Strachan et al., 1999; Schlacher et al., 2011). At Padre Island NS, campsites and picnicking areas are often located near

Table 5. Generalised linear model results for the three most common threat types (ghost crab [Ocypode quadrata] burrows, coyote [Canis latrans] tracks, and tidal inundation) and the cumulative number of threats to in situ Kemp’s ridley sea turtle (Lepidochelys kempii) nests among four regions (North, North Central, South Central, South) at Padre Island National Seashore, Texas, USA. SE: standard error; *: significant.

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the base of the foredune near the vegetation line, an area preferred by Kemp’s ridleys for egg deposition (Márquez-M., 1994; Culver et al., 2020). Overlap of human use with preferred nesting sites may attract ghost crabs and other predators to these areas, increasing the likelihood of nest depredation. In fact, higher densities and larger sizes of ghost crab burrows have been recorded at Padre Island NS in areas of increased use (Dixon et al., 2015). Interestingly, opposing trends in ghost crab and coyote activity over time may highlight the interrelationships between these species at Padre Island NS. Coyotes are a major predator of ghost crabs (Rose and Polis, 1998) and may play a significant role in controlling local crab populations. Similar trends have been seen on other beaches when predators were removed, resulting in increased ghost crab populations and inflating total predation pressure on sea turtle nests (Barton and Roth, 2008).

Incubating Kemp’s ridley clutches in protective corrals has been proven to be a highly successful recovery technique; for decades, nearly all clutches laid in Mexico were protected in corrals and nesting numbers increased exponentially from the mid-1980s through 2009 (NMFS et al., 2011; Bevan et al., 2016). However, when large arribadas occurred in Mexico in recent years, it was logistically impossible to translocate every clutch (Bevan et al., 2014). Therefore, starting in 2004, a subset of clutches at Rancho Nuevo have remained on the beach at the nest site to incubate in situ, though these sites are still monitored and are usually tightly clustered, increasing the likelihood to achieve predator swamping upon hatchling emergence (Bevan et al., 2014; Gallaway et al., 2016). Clutches relocated to protective corrals have higher hatching and emergence success in Mexico than clutches incubated in situ (NMFS et al., 2011; Bevan et al., 2014). At Rancho Nuevo, the mean emergence success for clutches protected in hatcheries from 1992–2003 was estimated to be 67.8% (NMFS et al., 2011), in contrast to 51.1% for clutches incubated in situ from 2009–2012 (Bevan et al., 2014). Bevan et al. (2014) also found that predation was reduced on beaches with higher nest densities, possibly due to predator swamping, a proposed survival strategy for the two arribada nesting species in the genus Lepidochelys. In Texas, mean maximum emergence success was 84.0% for clutches protected in hatcheries from 2000–2018; this high success rate is comparable to results from olive ridley sea turtle nests in Costa Rica, where protected nests had a hatch success rate of 83.1% compared to 21.6% for in situ nests (Clusella Trullas and Paladino, 2007). In addition, hatchling mortality

has been documented during the crawl from in situ nests to the ocean (7.6%; Erb and Wyneken, 2019). Eighty-seven percent of hatchlings successfully crawled to and entered the ocean from in situ nests in Mexico from 2009–2012 (Bevan et al., 2014). In contrast, for relocated clutches in Texas, 100% of live hatchlings are protected and enter the ocean.

At other nesting beaches, clutches from other sea turtle species are moved to higher ground or left in situ with protective cages, coverings, or screens. Leaving nests in situ avoids the risk of movement induced mortality of eggs that are not handled carefully during translocation (Limpus et al., 1979) and potential complications from altered thermal profiles within relocated nests (Pintus et al., 2009). Though reinforced in situ nests can fare significantly better than those left unmanaged in situ (Hopkins-Murphy and Seithel, 2005), these measures do not completely eliminate the threat of predation (Pheasey et al., 2018), inundation, or human impacts. Translocating more clutches to protective corrals has been recommended as the most expedient method of restoring the growth of the Kemp’s ridley population (Caillouet et al., 2016).

Of the 78 in situ nests we documented, 50 nests were observed to be negatively impacted by humans, predators, or both. Among these were 16 nests that were completely predated. At 10 nests, human interference was documented as crushed hatchlings from vehicle drive-over and visitor removal of hatchlings, eggs, or eggshells from the egg chamber. Clutches left in situ are at risk of interference by many anthropogenic activities, including illegal take of hatchlings and nest contents. Other anthropogenic activities can also harm incubating eggs, including accidental puncture from tent and shade structure stakes, increased sand temperatures from campfires, beach sand maintenance, trampling by human feet or horse hooves, digging holes on the beach, or contamination by refuse left on the beach. The Texas Open Beaches Act of 1959 describes all Texas beaches as roadways, and Padre Island NS’s enabling legislation allows public vehicle access to most of the 108 km of GoM beachfront in the park, with the southernmost 97 km only accessible from one beach access point, with no road behind the dunes. Additionally, due to the proximity of Padre Island NS to the USA/Mexico border, beach driving occurs year-round by personnel from local, state, and federal agencies for border security law enforcement purposes. From 1980–2018, fatalities of 42 hatchlings from in situ nests were documented after being struck by vehicles driving on the beach; had biologists and others not intervened at these sites

Donna J. Shaver et al.916

this total would likely have been greater. Furthermore, hatchlings emerging at night can become disoriented by artificial lighting (Price et al., 2018; Wilson et al., 2018; Stanley et al., 2020), and the light from buildings, vehicles, and campfires on the Texas coast may misorient hatchlings emerging in situ. In Texas, there are no state and typically no local prohibitions on beach use at night. Campfires are allowed on the beach unless the counties are under burning restrictions due to drought conditions and wildfire risk. No building lighting ordinances are in place because nesting is concentrated in protected undeveloped areas in south Texas, nesting remains relatively sparse in developed areas of the state, and most clutches are relocated to the protected areas.

During the 2005–2007 study, all but one of the marked sites monitored after translocation of eggs from the nest chamber were impacted by at least one of the following threats during the incubation period: tidal inundation, predator interaction, human tampering, vehicle drive-over, and/or plant root penetration, documenting the consistent threat to eggs left in situ. It is likely that marking the nest sites attracted more visitor attention to these areas and led to more frequent tampering. In contrast, removing eggs (and subsequently their smell) from these sites likely reduced the frequency of predator visitation. Impacts of ghost crab predation on sea turtle nests is a well-documented threat, resulting in mortality of as many as 82% of eggs left in situ (Marco et al., 2015). In the event in situ eggs survive the full incubation period, emerging hatchlings must survive additional encounters with predators such as ghost crabs, ants, and birds as they crawl towards the surf. Plant presence near in situ nests decreases hatching success by assisting invertebrate predation (Katilmis et al., 2006) and facilitates plant penetration into the nest, resulting in decreased moisture for developing eggs (Caldwell, 1959; Stegmann et al., 1988). Plant penetration into the nest may prevent hatchlings from emerging and vegetation near the nest may trap hatchlings as they crawl on the beach; facilitating predation and ultimately preventing hatchlings from entering the sea (Caldwell, 1959; Godfrey and Barreto, 1995).

Texas has significantly higher loads of beached marine debris than other USA states, mostly attributed to movement of debris in ocean currents, and has been identified as a national marine debris “hot spot” (Hardesty et al., 2017). Currently, debris accumulation rates are ten times greater along the Texas coastline than in northern GoM states (Wessel et al., 2019). In other states, removal of large debris has been shown to increase nesting activities in cleaned areas (Fujisaki

and Lamont, 2016). Heavy equipment is used to clean natural and anthropogenic debris from many areas of the Gulf beachfront in Texas, however, in areas that are not cleaned (i.e., the undeveloped parts of North and South Padre Islands; the primary Kemp’s ridley nesting beaches in the USA), Sargassum sp. and trash accumulate and can remain for long periods of time. In July and August, pelagic Sargassum sp. density in the Western GoM increases (Brooks et al., 2018), corresponding with the peak emergence period of Kemp’s ridley hatchlings. On beaches that are not cleaned, Sargassum sp. can accumulate to a depth of 1–2 m on the shoreline and form a continuous mat from the dune-line to near-shore Gulf of Mexico waters (Louime et al. 2017). Kemp’s ridleys typically nest a median distance of 12.9 m from the shoreline in Texas, and thus hatchlings would have to traverse this distance to reach the water (Culver et al., 2020). Hatchlings can become trapped or impeded during years when there are large amounts of beach Sargassum sp., as well as trash, items used by beachgoers (e.g., chairs, shade structures, tents, etc.), vehicle tracks, and holes dug in the sand (Lamont et al., 2002; Maurer et al., 2005; Ware and Fuentes, 2020).

Most of the 29 observed in situ emergences were between 0600 h and 1000 h, documenting that early morning daylight emergence regularly occurs for hatchlings of this species. It is difficult to quantify time of day for the 29 unobserved emergences (Fig. 2). On cloudy days, Kemp’s ridleys have been observed emerging through the morning and early in the afternoon (Márquez-M., 1994), and at Rancho Nuevo, Mexico, hatchlings have been documented emerging during early daylight hours (Bevan et al., 2015; Bonka and Wibbels, 2015). In situ hatchling emergence during mid-day can be dangerous if the hatchlings overheat before reaching the water. Twenty-two percent of the dead hatchlings documented in this study perished from heat and/or desiccation. Daytime emergence from in situ nests would also leave hatchlings more vulnerable to illegal take and other human impacts since public usage of beaches is greatest during daylight hours.

Seasonal climate events pose a significant danger to in situ nests at Padre Island NS. During the early summer months, the island is often subjected to intense drought periods. Conditions in the nest environment, including temperature and moisture, can have significant effects on the development of sea turtle eggs and emergence success (Tuttle and Rostal, 2010; Tanner et al., 2019). As temperature and the depth of dry sand increase, the emergence rate decreases (Márquez-M., 1994; Swiggs

Threats to Kemp’s ridley sea turtle nests incubating in situ on the Texas coast 917

et al., 2018). The Padre Island NS incubation facility monitors incubation temperatures and moisture of the sand, allowing control for the risk of hatchling mortality due to either high temperatures or large drying weather fronts. Similarly, for clutches incubated in outdoor corrals or in situ, these factors can be mitigated via watering and shading, which have been shown to lower sand temperatures (Hill et al., 2015; Esteban et al., 2018).

The substrate the nest is formed in also has an impact on hatching and emergence success of in situ nests. When beaches are nourished (where sand, often lost due to erosion, is replaced), sand from other sources can cause significant differences in the temperature, compaction, grain size, and moisture of the sand when compared to unnourished beaches (Grain et al., 1995). Clay and silt substrates critically dehydrate eggs early in the incubation period which can be lethal (Abella Pérez, 2011; Marco et al., 2017), or cause eggs to swell so that the embryos cannot pip the eggshells and need to be rescued or succumb (DJS, pers. observ.). Northern Texas beaches have sand with a higher clay content (Park and Edge, 2011), posing a serious risk to sea turtle eggs left in situ.

In situ nests can also be impacted by inundation caused by high tides, hurricanes, and coastal flooding events. In 2005, 14 sites from the marked nest study were in place when Hurricane Emily made landfall approximately 322 km south of the project location. Of those study sites, 71% were impacted, including six sites that were completely washed away and three others that were impacted by sand erosion or accretion. If these 14 clutches had been left in situ, it is likely that they all would have been destroyed. Emergence success is negatively correlated with sand water content (Patino-Martinez et al., 2014) and hatching success has been shown to decrease after seawater inundation (Caut et al., 2010). Beach flooding associated with tropical storms poses a severe threat (Vitousek et al., 2017), resulting in inundation and sand erosion at in situ nest sites and at corrals (if not properly positioned on the beach), however corrals reduce the risk of inundation from less severe storms that destroy in situ nests. Total emergence success, on beaches where all clutches are left in situ, has been shown to decrease by 14% during storm and post-storm years (Ehrhart et al., 2014). Water inundation was recorded at least once at 40% of the marked nest sites monitored from 2005–2007. Coastal flooding is an increasing threat at Padre Island NS (Sweet et al., 2019) and marked nest sites probably would have been inundated more frequently during recent years than when the 2005–2007 marked

nest site study was undertaken (P. Tissot, 2019, pers. comm.). Flooding of coastal beaches also increases sand salt content, which can lower hatching success (Bower et al., 2013). Elevated moisture levels increase the humidity within the nest, promoting bacterial and fungal colonisation of eggs, which have the potential to be opportunistic pathogens and cause embryonic death (Craven et al., 2007; Sarmiento-Ramírez et al., 2014; Rosado-Rodríguez and Maldonado-Ramírez, 2016).

Protected incubation will be an increasingly important tool to mitigate the impacts of climate change (Hill et al., 2015; Limpus et al., 2020). Every few years, thousands of loggerhead and green turtle eggs are destroyed on the eastern coast of the USA due to tidal inundation from tropical storm systems (Milton et al., 1994). From 2013–2017, 64% of Kemp’s ridley nests documented in Texas south of Padre Island NS were laid in areas deemed to be at high to very high risk of erosion (Wood, 2019), and likely would have been impacted by tidal inundation had they not been relocated to a protective corral. Climate scientists have hypothesised that sea level will rise, beaches will erode, and storm intensity and frequency will increase over time (IPCC, 2014), which would cause more frequent nest inundations that would be harmful to in situ nests (Hawkes et al., 2009). This has already been documented on Texas beaches where the frequency of high tide flooding events has increased more rapidly in recent years than in other areas in the USA due to both land subsidence as well as global sea level rise (P. Tissot, 2019, pers. comm.; Sweet et al., 2019).

Warming environmental conditions are expected to detrimentally alter hatchling sex-ratios (Hawkes et al., 2007) and many beaches are predicted to produce 100% females by 2070 (Fuentes et al., 2011), however, lethal incubation temperatures are thought to be a more immediate threat to species survival (Hays et al., 2017). In fact, Padre Island NS (and likely adjacent Kemp’s ridley nesting beaches in south Texas) is forecasted to experience a greater threat from rising temperatures and decreasing precipitation levels when compared to other areas of the USA (Gonzalez et al., 2018). The Kemp’s ridley is especially vulnerable to rising temperatures due to its restricted nesting range and unlikely ability to sufficiently expand its nesting range in response to climate change (Bevan et al., 2019). While natural beaches are faced with the impending crisis of completely feminised populations (Jensen et al., 2018) and low hatching success due to lethally high beach temperatures (Valverde et al., 2010; Hays et al., 2017; Laloë et al., 2017; Bevan et al., 2019), nest

Donna J. Shaver et al.918

management techniques, such as those used at Padre Island NS and on South Padre Island, can mitigate these threats. Relocating clutches to either a temperature controlled laboratory facility or corral, and using tested management techniques (e.g., sand watering [Hill et al., 2015] and shading [Patino-Martinez et al., 2012b; Wood et al., 2014; Hill et al., 2015; Liles et al., 2019]), gives flexibility to mitigate for threats caused by climate change, sea level rise, and other factors.

Although the Kemp’s ridley was showing promising signs of recovery, abrupt declines in nesting observed in Texas and Mexico have renewed concern regarding the future of the Kemp’s ridley sea turtle (Caillouet, 2014; Plotkin and Bernardo, 2014; Shaver and Caillouet, 2015). Though the cause of the decline is still uncertain, the Deepwater Horizon oil spill, reductions in prey availability, and increases in the re-migration interval of nesting females could have contributed to the setback of the population (Caillouet et al., 2016; Shaver et al., 2016). The long-term trend for Kemp’s ridley recovery is uncertain, with some population modelers predicting return to exponential increase (Kocmoud et al., 2019) and others predicting that numbers have reached density dependence in juvenile foraging grounds (Caillouet et al., 2018).

Conclusions.— Clearly, sea turtle nests left in situ along the Texas coast face a complex matrix of environmental, biological, and anthropogenic threats requiring targeted, well-informed management techniques to reduce nest loss and hatchling mortality while allowing for human use of Texas beaches as mandated by local, state, and federal laws. After evaluation of the results from the study of marked nest sites from 2005–2007 and of observations of in situ nests over the past 38 years, we conclude that the recovery of the nesting population of the critically endangered Kemp’s ridley in Texas depends on the continued relocation of clutches to incubation facilities and protected corrals. Leaving clutches in situ on the Texas coast is not advised at this time, until nest levels and densities increase sufficiently to swamp predators and achieve sustainable population levels at the secondary nesting colony at Padre Island NS, and other mortality factors are controlled in Texas. Protected incubation and hatchling release must be continued to ensure maximum recruitment into the growing secondary nesting colony from eggs laid in Texas.

Acknowledgements. We thank the individuals and organisations that aided with detection, monitoring, and reporting of nests included in this analysis. Amos Rehabilitation Keep, Turtle

Island Restoration Network, National Marine Fisheries Service, National Park Service, Sea Turtle, Inc., Texas A&M University at Galveston, U.S. Fish and Wildlife Service, U.S. Geological Survey, University of Texas, and others provided assistance or funding for nest detection and protection activities in Texas. Work by Padre Island NS personnel was authorised under FWS Permit TE840727-3, Texas Parks and Wildlife Department Scientific Permit SPR-0190-122, and NPS Institutional Animal Care Protocols NPS IACUC 2011-15 and IMR_PAIS_Walker_SeaTurtles_2016.A3. Comments from C. Hart and E. Cuevas improved the manuscript greatly. Thank you to M. E. Rasmussen for aiding with data organisation, M. R. Villalba-Guerra for aiding with literature compilation, and S. A. Laughlin for editorial assistance. We thank P. Tissot for providing insight regarding current and expected Texas beach conditions and why these support the need for nest relocation. In memory of A. F. Amos for years of dedicated monitoring and collaboration.

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Accepted by Graham Walters

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