Hatchling Production Research Articles

Potential drivers and implications of a balanced breeding sex ratio in a small population of an imperiled species with environmental sex determination.

Small populations of imperiled species are susceptible to the negative consequences of skewed sex-ratios. In imperiled species with environmental sex determination such as sea turtles, examining sex ratios across a range of environments and population abundance levels can provide insight into factors that influence population resilience, which can then be the foci of management plans for these species. Breeding sex ratios (the ratio of actively breeding males to females during a reproductive season; BSRs) extrapolated from genetic parentage analyses are a common approach for enumerating sex ratios in sea turtles. Such analyses also allow for the characterization of multiple paternity within sea turtle clutches, which should reflect BSRs and breeding behaviors. We characterized the first BSR for a breeding assemblage of loggerhead sea turtles (Caretta caretta) belonging to the temperate, low-abundance Northern Gulf of Mexico Recovery Unit using genotypes of 16 microsatellite loci from nesting females and hatchlings. Unlike prior studies at both more-tropical and more-temperate, and higher-abundance, Recovery Units in this region, we found a balanced BSR of 1.3:1 males:female and a low incidence (~17%) of multiple paternity. This suggests that there are relatively few males breeding at this assemblage and within this Recovery Unit. Beaches in this region are expected to produce substantial numbers of male hatchlings based on sand temperature data. The relative dearth of mature males may then be due to hydrologic disturbances that disproportionately affect the fitness and survival of male hatchlings, or due to demographic stochasticity. More work is needed to study the factors that might influence male hatchling production and fitness in this region, particularly as climate change is predicted to lead to feminization in global sea turtle populations. Our work demonstrates the broad utility of characterizing BSRs and other sex ratios across a range of populations in imperiled, environmentally sensitive species.

Water budgeting for production of hatchlings, fry and fingerlings of Asian catfish, Clarias magur

Studies were conducted to estimate the consumptive water use to produce hatchling (HL), fry (FY), and fingerlings (FL) of magur, Clarias magur in hatchery system. Aeration and water flow rate largely influenced the production of viable and deformed hatchlings in magur. In hatchling production, the HL-6 treatment group with 28 h water flow and 28 h aeration had the highest hatching rate (88%), followed by HL-5 with 28 h water flow (83%), whereas treatments HL-1 and HL-2 with 0 h and 14 h aeration, respectively, with no water flow failed to produce any hatchling. HL-6 had the minimal consumptive water use (CWU) of 530 ± 11 litres for 1000 viable hatchlings production among the treatments. In 2nd study on rearing of larvae to fry with five water exchange schedules (25, 50, 75% daily, 75% in alternate days and 75% in two days once), significant differences in the growth and survival of larvae were observed among the treatments. Survival was significantly higher (98–99%) in the FY-1 and FY-2 treatment group with 25% and 50% water exchange daily, respectively. The most efficient CWU to produce 1000 fry was found to be 1068 litres (935 fry m−3 water) for FY-1 with 25% water exchange daily. The 3rd study was conducted for ten weeks in outdoor tanks to optimize the water requirement for rearing of fry to fingerlings with 10, 20 and 30% water exchange per week. The highest growth (2.34 g) and survival (83%) (P < 0.05) were observed in FL-3 treatment receiving weekly exchange of 30% water. But in terms of water use and better survival rate, FL-2 water exchange (20%) group level showed the better survival rate (70%) and CWU of 5121 L for 1000 fingerlings production suggesting it to be the most water-efficient outdoor fingerling production system for magur.

A roadmap for multiple paternity research with sea turtles.

There have been multiple paternity studies across many taxa, including birds, reptiles and insects, for many decades. Sea turtles are by far the most studied of any group of reptiles with up to ten fathers recorded for a clutch and multiple paternity in over 90% of clutches in some populations. Whether multiple paternity has any adaptive significance remains a key question in sea turtles, since the impact of environmental conditions often seems to swamp any impact of the incidence of multiple paternity. Climate warming and the resulting threat of feminisation of sea turtle populations is set to provide an intense new focus for studies. If male turtles become increasingly scarce as a result of warming incubation temperatures, then management intervention will be needed to promote male hatchling production. Multiple paternity studies may help inform when intervention is needed, with the expectation that the incidence of multiple paternity will decline as breeding males become scarce.

Sex Ratio Estimation of Green Turtle Hatchlings in Kazanlı Beach, Türkiye

Sea turtles are distributed worldwide, mostly in the tropical and subtropical waters. All seven species of sea turtles in the world have temperature-dependent sex determination. The pivotal temperature for hatchlings with a female:male ratio of 1:1 is usually around 29°C. Female hatchlings are observed at values higher than the pivotal temperature and male hatchlings at lower values. It is expected that wildlife threatened by global warming will be more severely affected, especially species that sex is determined by temperature. This study was carried out by measuring air, sand and nest temperatures during two nesting seasons at Kazanlı Beach, one of the largest nesting sites of Chelonia mydas (Green turtle) in the Mediterranean. Sand grain size was also measured, and gonads of dead hatchlings were examined histologically. Both sand (n=4) and nest (n=6) temperatures were above the pivotal temperature (between 29.1-31.6°C) in the study area. According to the estimation based on temperatures, hatchlings were female (♀&amp;gt;50%) biased. Of the hatchling samples, 75 were examined histologically. According to histological examination, the female:male ratio was 2:1. According to the direct examination and indirect estimation; the sex ratio of green turtle hatchlings in Kazanlı Beach, one of the highest hatchling producing nesting sites of the Mediterranean, was reported for the first time in this study. There is a need to fill the data gaps regarding sex ratios, especially for major beaches with high hatchling production. Knowing the temperature profiles in and around the nest and sex ratios of hatchlings is critical for the development of conservation measures for endangered sea turtles.

Physiological and behavioral assessment of Metaphire posthuma in response to clothianidin insecticide: Insights from molecular and biochemical analysis

In the present study, Clothianidin [(E) - 1-(2 - chloro-1,3 - thiazol - 5-ylmethyl) - 3-methyl - 2- nitroguanidine] (CLO) was selected as a soil pollutant and earthworm was employed as a test organism. The various responses like biochemical and detoxification process of earthworm Metaphire posthuma towards Clothianidin at lethal and sublethal doses were studied using OECD-standardized toxicological guidelines. The present study examined the toxicity of CLO to earthworms after 28 days of exposure at conc. 0, 1.5, 3, 6, 12 and 24 mg kg−1 in a soil mixture. Biochemical markers including Guaiacol peroxidase (POD), Superoxide dismutase (SOD), Catalase (CAT), Glutathione S-transferase (GST) and content of Malondialdehyde (MDA) in earthworms were measured. Acute toxicity tests revealed that CLO caused a concentration-dependent increase in mortality with LC50 (Lethal concentration) values of 10.960 and 8.201 mg kg−1 for 7th and 14th day respectively. The earthworms were exposed to CLO contaminated soil for 56 days and reflecting the significant decrease in earthworm growth, cocoon and hatchling production. Moreover, enzyme activities such as CAT, SOD, POD and MDA content were significantly enhanced with the increased concentration and exposure period of CLO. Molecular docking studies indicated that CLO primarily interacts to the junction site of SOD and in active centres of CAT, POD and GST. As a result, the current findings imply that the sub chronic CLO exposure can induce variations in physiology and avoidance behaviour of earthworms, oxidative stress as well as alterations in enzyme activities.

A case study assessing the impact of mating frequency on the reproductive performance of the Hawaiian bobtail squid Euprymna scolopes

BackgroundThe symbiosis between the Hawaiian bobtail squid Euprymna scolopes and bacterium Vibrio fischeri serves as a model for investigating the molecular mechanisms that promote the initial formation of animal-bacterial symbioses. Research with this system frequently depends on freshly hatched E. scolopes, but the husbandry factors that promote hatchling production in a mariculture facility remain underreported. Here we report on the reproductive performance of E. scolopes in response to decreased mating frequency.ResultsOne animal cohort was maintained in a mariculture facility for 107 days, with females assigned to either a control group (mating once every 14 days) or an experimental group (mating once every 21 days). No differences between the groups were observed in survival, the number of egg clutches laid, or hatchling counts. Each group featured multiple females that were hyper-reproductive, i.e., they generated more than 8 egg clutches while in captivity. Examination of the distributions for daily hatchling counts of individual egg clutches revealed significant variation in the hatching patterns among clutches that was independent of mating frequency. Finally, an assessment of hatchling production showed that 93.5% of total hatchlings produced by the cohort were derived from egg clutches laid within the first 70 days.ConclusionsThese results suggest a lower mating frequency does not impede hatchling production. Furthermore, the variation in hatchling production among egg clutches provides new insight into the reproductive performance of E. scolopes as a lab animal for microbiology research.

Hidden demographic impacts of fishing and environmental drivers of fecundity in a sea turtle population.

Fisheries bycatch is a critical threat to sea turtle populations worldwide, particularly as turtles are vulnerable to multiple gear types. The Canary Current is an intensely fished region, yet there has been no demographic assessment integrating bycatch and population management information of the globally significant Cabo Verde loggerhead turtle (Caretta caretta) population. Using Boa Vista island (Eastern Cabo Verde) subpopulation data from capture-recapture and nest monitoring (2013-2019), we evaluated population viability in combination with estimated regional bycatch rates (2016-2020) in longline, trawl, purse-seine and artisanal fisheries. We further evaluated current nesting trends in the context of bycatch estimates, existing hatchery conservation measures, and environmental (net primary productivity) variability in turtle foraging grounds. Current bycatch mortality rates present a risk of near extinction this century, when projecting the Boa Vista subpopulation with matrix population models. Bycatch reduction could increase finite population growth rate by 1.95%, and 1.76% for longline fisheries alone. Hatchery conservation increases hatchling production and reduces extinction risk, but cannot achieve population growth alone. Short-term increases in nest counts (2013-2021), putatively driven by temporary increases in net primary productivity, may be crucially masking ongoing long-term population declines. When fecundity was linked to net primary productivity, our hindcast models simultaneously predicted these opposing long-term and short-term trends. Consequently, our results show conservation management must diversify from land-based management. The masking effect we found has broad-reaching implications for monitoring sea turtle populations worldwide, demonstrating the importance of directly estimating adult survival and that nest counts might inadequately reflect underlying population trends. This article is protected by copyright. All rights reserved.

Reassessment of the olive ridley sea turtle Lepidochelys olivacea nesting population at Nancite Beach, Costa Rica

AbstractNancite is a fully protected beach within the Guanacaste Conservation Area, Costa Rica where olive ridley (Lepidochelys olivacea) sea turtles nest in synchronous mass‐nesting events known as arribadas. Arribadas decreased in magnitude at this beach by approximately 90% during the period 1971–2007 due to unknown causes. The total count estimate of females nesting in a year also decreased over these decades. In the present study, from August 2009 to February 2021, the trend of arribada nesting female abundance and estimated annual production of hatchlings were assessed and compared with previous trend analyses. A total of 62 mass‐nesting events were quantified in the period 2009–2021, with an estimated annual average of 64,694 nesting females. Trend analysis indicated that during our recent study period, the number of females per arribada event increased by an estimated 14% (8%, 20% CI95%). During this period, a mean hatching rate of 33.4% was estimated, corresponding to an overall estimated production average of 2,165,597 per season, which represented an increase of 82.7% compared with a previous estimate for the period 1980–1984, when the arribadas were larger. We suggest that the growth in hatchling production over the past four decades is at least in part responsible for the slight increase in the estimated size of arribadas since 2009/2010. However, because maximal hatching success did not increase above 60%, the beach may be close to reaching carrying capacity, and it seems that high hatchling production may soon level off or begin to decrease. Thus, it is not clear whether current hatchling production will lead to the recovery of the Nancite population to the historical levels documented in the 1970s and early 1980s.

Red-cockaded woodpecker habitat characteristics associated with partial brood loss in the Upper East Gulf Coastal Plain, USA

Some red-cockaded woodpecker (RCW) Dryobates borealis populations remain understudied. This is notable because management that incorporates population demographics and site characteristics may benefit RCW recovery. The Oakmulgee Ranger District of the Talladega National Forest (Alabama, USA) has no wiregrass Aristida stricta, small forest stand sizes, rolling topography, and contains an understudied RCW population. Our goal in the Oakmulgee was to characterize RCW habitat, possibly identify ways in which habitat differed from other regions, and estimate associations between habitat and reproductive output. We found that 70.2 and 92.5% of sampled stands met recovery standard thresholds for small and large pine basal area (BA) as defined in the United States Fish and Wildlife Service (USFWS) RCW Recovery Plan. While 74.6% of longleaf pine Pinus palustris-dominated stands met the threshold for overstory hardwood canopy composition, 60.0% of loblolly pine P. taeda-dominated stands did not. Few stands met the recommended percentage of herbaceous understory (19.8%) or recommended absence of hardwood midstory. A lower rate of partial brood loss was associated with a greater area of large pines (≥25.4 cm diameter at breast height; DBH), a smaller area of small pines (≥10 and &lt;25.4 cm DBH), a larger area burned in the dormant season, and higher RCW density. In our models, hardwood overstory and midstory did not influence egg or hatchling production. Hardwoods in the Oakmulgee could contribute to unfavorable habitat, as indicated in the USFWS RCW Recovery Plan, as well as relate to variation in habitat across the RCW’s range. Regions of the RCW’s range are understudied, and limited staffing and funding impede advances in understanding and conservation.

Modeling the impacts of temperature during nesting seasons on Loggerhead (Caretta caretta) Sea Turtle populations in South Florida

Loggerhead sea turtles (Caretta caretta) are a threatened sea turtle species that nests on beaches along the northwestern Atlantic Ocean. Loggerhead nesting in Florida accounts for approximately 80% of the loggerhead population in the Atlantic Ocean, yet the underlying ecological mechanisms behind their population dynamics are understudied. C. caretta are largely inaccessible since they spend most of their early life in open ocean habitats. Consequently, their nesting and hatchling production offer quantifiable insight of their population dynamics. Emergence success, the proportion of eggs laid that produce offspring which successfully leave the nest, is the source of all later life stages. Yet the abiotic factors that drive emergence success trends have not been fully described. This study explores the relationship between air temperature and emergence success across multiple nesting seasons to better understand the potential impact of anthropogenic climate change on subsequent loggerhead populations. Here we investigate the effect of changing emergence success on the juvenile and adult life stages. After exploring numerous aspects of temperature and precipitation metrics, we determined that the mean of the maximum daily temperatures for each trimester of the eggs’ incubation periods related most closely to the variation in emergence success (the proportion of hatchlings that make it out of the nest) across nests. A novel feature of our approach to modeling the impact of temperature on the later life stages is through connecting a statistical model into a discrete mechanistic population model. Our population model has two parts, one with eggs and hatchlings on a daily time scale in the nesting season and the other with juveniles and adults on an annual time scale. The statistical model enables us to illustrate the effect of temperature changes across these life stages. The decline in the adult population follows from the decline of the hatchling emergence success. Using predicted increases in temperature due to climate change, we illustrate a corresponding prediction for the population classes.

Can a present-day thermal niche be preserved in a warming climate by a shift in phenology? A case study with sea turtles.

How species respond to climate change may impact their extinction probability. Here we link climatology and ecology to tackle a globally important conservation question. For sea turtles, there are concerns that climate warming will cause both the feminization of populations as well as reduced hatchling survival. For 58 nesting sites across the world spanning all seven sea turtle species, we investigated whether warming might be avoided by shifts in nesting phenology to a cooler part of the year. We show that even with the most extreme phenological shift that has been reported to date-an 18-day advance in nesting per °C increase in sea surface temperature (SST)-temperatures will continue to increase at nesting sites with climate warming. We estimate that SST at nesting sites will rise by an average of 0.6°C (standard deviation = 0.9°C, n = 58) when we model a 1.5°C rise in SST combined with a best-case-scenario shift in nesting. Since sea turtles exhibit temperature-dependent sex determination, these temperature rises could lead to increasingly female-biased sex ratios as well as reduced hatchling production at sites across the world. These findings underscore concerns for the long-term survival of this iconic group.

Multidecadal fluctuations in green turtle hatchling production related to climate variability

The state of Campeche, Mexico, harbors one of the largest green turtle (Chelonia mydas) rookeries of the Wider Caribbean Region. Since the 1970s, harvesting of this population was common practice, but it has since ceased, and the population is rebounding as a consequence. In this rookery, during the past 37 years (1984–2020), the positive relationship between the annual number of nesting females and the number of hatchlings they produce has revealed a long-term population signal that we postulate could be related to environmental factors. To investigate this relationship more deeply, we adopt a stock-recruitment (SR) approach, which is commonly used in fisheries. Regression analysis methods for the SR relationship, including a dynamic version of the model that incorporates the effect of sea surface temperature, show that the number of recruits produced and the number of hatchlings per unit nester were significantly and inversely correlated with a 26-year cycle of the Atlantic Multidecadal Oscillation (AMO) with a three year lag. A possible explanation for this finding is that environmental conditions during warming periods of the 26-year AMO cycle may negatively affect hatchling production by altering the nest moisture content during the incubation period, and increasing embryonic mortality, while the annual female abundance at nesting beaches may decrease due to trophic effects. The time series of abundance corresponding to other population units of green turtles as well as other species of sea turtles in the Gulf of Mexico present a similar behavior to that evaluated here, suggesting a basin-wide environmental effect.

Operational sex ratio estimated from drone surveys for a species threatened by climate warming

Rising sand temperatures resulting from climate warming may cause the ‘feminization’ of sea turtle populations, which have temperature-dependent sex determination. In July and October 2021, we conducted surveys using a drone (also referred to as an unmanned aerial vehicle or UAV) and shore-based observations to assess the operational sex ratio (OSR) (number of males and females in breeding condition) for green turtles (Chelonia mydas) in the southern Great Barrier Reef, Australia (23.44 °S, 151.92 °E). Using drone-imagery, the length:width (L:W) ratio of a turtle’s head was used to distinguish loggerhead turtles (Caretta caretta) from green turtles, and the L:W of the carapace was used to distinguish juveniles from adult-sized green turtles. The first breeding pair was observed in shore-based surveys on 14 September 2021 and the number of mating turtles then increased to a peak on 4 October, about 8 weeks before the peak in nesting. A total of 94 km of drone transects with associated video footage was analysed. In October, at the peak of the mating season, the ratio of adult turtles displaying breeding behaviours near the island was 0.51 female (95% CI ± 0.17), supporting previous conclusions that despite the female-biased (> 80%) hatchling sex ratio, this population likely has a fairly balanced OSR. These findings are likely explained by males breeding 2–3 times more frequently than females, which helps mitigate female-biased hatchling sex ratios. Assessing the OSR of populations with extreme female hatchling bias may help to inform whether intervention is needed to increase male hatchling production.

Beach reprofiling to improve reproductive output at the world’s largest remaining green turtle rookery: Raine Island, northern Great Barrier Reef

Raine Island is a low-lying reef island located on the outer edge of the northern Great Barrier Reef (nGBR). It is part of the Raine Island National Park (Scientific) and is managed to protect and conserve its exceptional natural, cultural, ecological and scientific values. High amongst these values is Raine Island's importance as the world's largest green turtle (Chelonia mydas) rookery. However, since at least the late 1990s the number of turtle hatchlings produced from nests on the island has significantly declined. The ramifications of reduced hatchling production at Raine Island for the nGBR green turtle population resulted in the establishment of the Raine Island Recovery Project (RIRP), a 5-year $AUS 7.95 million collaborative project involving government, industry and Traditional Owners. A primary aim of the RIRP is to restore viable turtle nesting habitat on Raine Island. Although reduced hatchling production and the potential demise of the nGBR green turtle population are very much an ecological concern, the key to understanding and addressing this management issue is largely geomorphological. Here we detail how the geomorphological attributes of Raine Island contributed to the drop in hatchling output, and outline how understanding and working with the geomorphology and coastal processes at Raine Island have contributed to the mitigation of that decline. In particular, geomorphological investigations established that the sand losses that have reduced the elevation of turtle nesting beaches were unlikely to be replenished by natural processes, and they informed strategic movements of beach sand to increase nesting habitat above tidal inundation which has boosted hatchling production by as much as 640,000 over the past five years. Although this outcome is undoubtedly a success, the future remains challenging as anthropogenic climate change impacts progress.

Investigating the effectiveness of a well‐managed hatchery as a tool for hawksbill sea turtle (Eretmochelys imbricata) conservation

AbstractThe critically endangered hawksbill sea turtle (Eretmochelys imbricata) is of conservation concern worldwide. Conservation actions which act to reduce high levels of embryonic mortality aid to boost hatchling production. At Cousine Island, Seychelles, a mixed management method has been adopted to maximize the number of hatchlings entering the ocean. We examined the effectiveness of a hatchery at increasing hatching and emergence success from four seasons of data (2017–2021). Hatchery nests had significantly higher hatching and emergence success across all years relative to nests left in situ (i.e., natural), with inter‐annual variation observed. A greater percentage of in situ clutches was found to be influenced by both crab activity and predation as compared to relocated clutches. Overall, the mixed management approach increased hatching success (mean = 75.1%) relative to the various nest management techniques previously used (2004/2005–2016/2017; mean = 63.5%). By mitigating external influences such as tidal flooding, beach erosion, and crab activity/predation, this study provides evidence for the success of a hatchery in directly increasing hatchling recruitment. Strict and careful hatchery management as well as timely and efficient relocation procedures are needed to minimize potential negative effects of nest relocation.

Potential impacts of sea level rise and beach flooding on reproduction of sea turtles

Climate change scenarios predict an increase in global temperature and sea level rise. For sea turtles, the association between sea level rise, nest water content and temperature along the beach may influence embryo development and offspring survival. Over three consecutive years (2016 – 2018), a field experiment was conducted on Boa Vista island, Cabo Verde, to assess the potential impacts of tidal inundation on hatching success and hatchling phenotype in loggerhead sea turtles (Caretta caretta). Ninety-three groups of three nests each (N = 279) were relocated to a 5 km stretch of the same beach. Nests in each group were placed at regular intervals of 30 to 60 m across three zones of the beach: the lower “wet” zone, where tidal inundation was a risk, a middle zone, and the upper vegetated zone. Mean emergence and hatching success in the wet treatment was 12.0% and 18.9% respectively. In the middle zone it was 25.6% and 39.5%. In the vegetated zone it was 47.2% and 57.1%. Male hatchling production was severely reduced in the wet zone, probably by nest inundation, with the few hatchlings produced being predominantly male. Female body size and clutch size both had a significant impact on hatchling production and hatchling phenotype. In response to increased global temperatures, male hatchling production may continue in nests laid in areas of high flooding risk. The relocation of clutches to the upper beach areas as a conservation plan could be implemented to reduce the mortality of nests by high tide.

Trends in abundance and reproductive success of the hawksbill turtle nesting population at Buck Island Reef National Monument, St. Croix, US Virgin Islands

Index nesting sites for the Critically Endangered hawksbill turtle Eretmochelys imbricata are essential for assessing population trends and demographics, and informing conservation strategies. Using 29 yr (1988-2017) of saturation tagging data from a protected Caribbean index site, we assessed annual trends in abundance and reproductive success for the hawksbill nesting population at Buck Island Reef National Monument (BIRNM), St. Croix, US Virgin Islands. Approximately 43 ± 21 (mean ± SD) females and 154 ± 60 nests were encountered each year during nocturnal patrols. Remigration interval and inter-nesting period averaged 3.2 ± 1.6 yr and 17.4 ± 7.1 d, respectively. After a significant recovery since 1988, female abundance stabilized during 2007-2017 (p &lt; 0.01, R2 = 0.82), whereas nest abundance declined (p &lt; 0.01, R2 = 0.71) and neophyte recruitment exhibited a decreasing trend. There was no trend in annual mean hatch success (69.4 ± 26.6%), emergence success (63.0 ± 29.1%), and hatchling production (89.2 ± 45.0 individuals clutch-1) during the study period; but clutch size (p &lt; 0.01, R2 = 0.65; 142.8 ± 28.9 eggs clutch-1) and female curved carapace length (p &lt; 0.01, R2 = 0.56; 88.4 ± 4.7 cm) significantly decreased. The BIRNM population has stabilized, but declines in body size and nest abundance highlight the need for evaluating demographics to diagnose the factor(s) driving changes in abundance and productivity. Our study provides a foundation for evaluating Caribbean hawksbill demographics, while contributing a valuable assessment of clutch size and in situ nest success for the species.

Short-term gain, long-term loss: How a widely-used conservation tool could further threaten sea turtles

Sea turtles nest on tropical and subtropical beaches, where developmental success of egg clutches depends on nest temperature. Higher nest temperatures increase embryo and hatchling mortalities and produce female hatchlings. Nest shading has been used on some beaches to reduce nest temperatures, and thereby increase number of hatchlings and reduce female-biased sex ratios. We modeled short- and long-term effects of reducing mean nest temperatures on a leatherback turtle (Dermochelys coriacea) population for which the effect of temperature on sex ratios and emergence success (# hatchlings emerged/ # eggs) is well-established. We simulated mean nest temperature reductions of −0.5 °C, −1 °C, −1.5 °C and −2 °C in relation to current mean (30.4 °C) and projected population responses over 100 years. Additionally, we run climate change simulations of +0.5 °C, +1.0 °C and +2.0 °C to assess if shading could be needed after passing a certain threshold.Emergence success increased with reduced nest temperatures. However, lowering nest temperatures ultimately caused long-term declines in number of nesting females and total population size, because the number of female hatchlings was reduced. Because hatcheries are a widely-used conservation tool, caution must be used to avoid reducing the number of female hatchlings by lowering nest temperatures. Nest cooling may only be needed under critically low hatchling production and extremely biased female sex ratios that we only found at +2.0 °C. If nest shading is to be used, it should be applied strategically to optimize hatchling production with natural sex ratios to achieve both short-term conservation goals and long-term population sustainability.

Influence of short-term temperature drops on sex-determination in sea turtles.

All sea turtles exhibit temperature-dependent sex-determination, where warmer temperatures produce mostly females and cooler temperatures produce mostly males. As global temperatures continue to rise, sea turtle sex-ratios are expected to become increasingly female-biased, threatening the long-term viability of many populations. Nest temperatures are dependent on sand temperature, and heavy rainfall events reduce sand temperatures for a brief period. However, it is unknown whether these short-term temperature drops are large and long enough to produce male hatchlings. To discover if short-term temperature drops within the sex-determining period can lead to male hatchling production, we exposed green and loggerhead turtle eggs to short-term temperature drops conducted in constant temperature rooms. We dropped incubation temperature at four different times during the sex-determining period for a duration of either 3 or 7 days to mimic short-term drops in temperature caused by heavy rainfall in nature. Some male hatchlings were produced when exposed to temperature drops for as little as 3 days, but the majority of male production occurred when eggs were exposed to 7 days of lowered temperature. More male hatchlings were produced when the temperature drop occurred during the middle of the sex-determining period in green turtles, and the beginning and end of the sex-determining period in loggerhead turtles. Inter-clutch variation was evident in the proportion of male hatchlings produced, indicating that maternal and or genetic factors influence male hatchling production. Our findings have management implications for the long-term preservation of sea turtles on beaches that exhibit strongly female-biased hatchling sex-ratios.

Exposure of Loggerhead Sea Turtle Nests to Waves in the Florida Panhandle

Wave wash-over poses a significant threat to sea turtle nests, with sustained exposure to waves potentially resulting in embryonic mortality and altered hatchling locomotor function, size, and sex ratios. Identifying where and under what conditions wave exposure becomes a problem, and deciding what action(s) to take (if any), is a common issue for sea turtle managers. To determine the exposure of sea turtle nests to waves and identify potential impacts to hatchling productivity, we integrated a geographic information system with remote sensing and wave runup modeling across 40 nesting beaches used by the Northern Gulf of Mexico Loggerhead Recovery Unit. Our models indicate that, on average, approximately 50% of the available beach area and 34% of nesting locations per nesting beach face a significant risk of wave exposure, particularly during tropical storms. Field data from beaches in the Florida Panhandle show that 42.3% of all nest locations reported wave exposure, which resulted in a 45% and 46% decline in hatching and emergence success, respectively, relative to their undisturbed counterparts. Historical nesting frequency at each beach and modeled exposure to waves were considered to identify priority locations with high nesting density which either experience low risk of wave exposure, as these are good candidates for protection as refugia for sustained hatchling production, or which have high wave exposure where efforts to reduce impacts are most warranted. Nine beaches in the eastern Florida Panhandle were identified as priority sites for future efforts such as habitat protection or research and development of management strategies. This modeling exercise offers a flexible approach for a threat assessment integration into research and management questions relevant to sea turtle conservation, as well as for other beach species and human uses of the coastal environment.