Effects of supplemental watering on loggerhead (Caretta caretta) nests and hatchlings

Lolavar, Alexandra; Wyneken, Jeanette

doi:10.1016/j.jembe.2020.151476

Cited by 13 publications

(10 citation statements)

References 69 publications

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“…A similar finding was observed by Jourdan & Fuentes (2015), with irrigation applied during daylight hours eliciting an increase in sand temperature at nest depth. These findings highlight the important interaction be tween water temperature and the volume of water applied when contemplating cooling nests using irrigation (Naro-Maciel et al 1999, Lolavar & Wyneken 2021.…”

Section: Irrigation Regimesmentioning

confidence: 90%

“…However, artificial shade structures typically only decrease nest temperature by 1−2°C (Wood et al 2014, Esteban et al 2018, Reboul et al 2021, which is often not enough to induce male hatchling production. Also, nesting sites predicted for complete feminisation are often remote and may lack the resources and infrastructure required to implement these common management strategies (Hill et al 2015, Jourdan & Fuentes 2015, Lolavar & Wyneken 2015, Lolavar & Wyneken 2021. Although seawater is ubiquitous at marine turtle nesting beaches and may be an effective way to cool beach sand, it has not been previously investigated as a potential mitigation strategy to combat high nest temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Trialling seawater irrigation to combat the high nest temperature feminisation of green turtle Chelonia mydas hatchlings

Smith¹,

Booth

Crosby

et al. 2021

Mar. Ecol. Prog. Ser.

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Global increases in beach sand temperatures are predicted to skew hatchling sex ratios of marine turtle populations towards female bias. Currently, shade structures and freshwater irrigation are management strategies used to cool nest temperatures, but require resources that are limited at remote rookeries. Here, we report on a novel investigation that used seawater irrigation as a sand-cooling method. Various volumes of seawater were applied to sand to determine the optimal application required to lower sand temperatures at nest depth to produce male-biased sex ratios. We performed these experiments during the 2019-2020 nesting season at Heron Island on the southern Great Barrier Reef, Australia, and at Panasesa Island, Papua New Guinea. We found the amount of cooling at nest depth was site dependent and varied with the seawater irrigation regime used. At Heron Island, we used a one-off application of the equivalent of 120 mm of rainfall either as freshwater or seawater to the sand above incubating clutches 18 d after oviposition to determine whether this affected the hatching success of green turtle Chelonia mydas eggs. Both treatments had higher hatching success (83.8 ± 3.5% and 71.2 ± 6.3%, respectively, means ± SE) compared to control clutches (63.5 ± 6.0%). Our results indicate that a one-off application of seawater may be an effective management option for reducing nest temperatures during the sex-determining period of marine turtle clutches incubating in situ. Seawater irrigation could be used in areas where populations are at highest risk of feminisation caused by a hot drying climate where freshwater is not available for irrigation.

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Section: Irrigation Regimesmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Trialling seawater irrigation to combat the high nest temperature feminisation of green turtle Chelonia mydas hatchlings

Smith¹,

Booth

Crosby

et al. 2021

Mar. Ecol. Prog. Ser.

View full text Add to dashboard Cite

show abstract

“…Although in most places interventions are not needed, in areas where most egg clutches are already incubated in hatcheries due to a number of threats (e.g., high risk of egg poaching or tidal inundation; Chacón-Chaverri and Eckert 2007;Mutalib and Fadzly 2015), PA-PSR and PET could guide management actions. For example, nest shading and irrigation have been proposed to lower nest temperatures and increase hatching success (Hill et al 2015;Jourdan and Fuentes 2015;Lolavar and Wyneken 2021;Smith et al 2021), but this could also reduce the number of female hatchlings and cause population declines in the long term (Santidrián Tomillo et al 2021). Thus, using PET to reach current PA-PSRs would be a better strategy than using the PT to reach equal sex ratios in hatchlings, where the environmental conditions of nests are already being controlled.…”

Section: Discussionmentioning

confidence: 99%

When population-advantageous primary sex ratios are female-biased: changing concepts to facilitate climate change management in sea turtles

Tomillo

2022

Climatic Change

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Sea turtles have temperature-dependent sex determination. Because females are produced at high temperatures, increasing global temperature may lead to population feminization. Primary sex ratios (PSR) of sea turtle hatchlings are naturally female-biased, but this translates into a more balanced operational sex ratio because male turtles reproduce more often than females. As a consequence, a balanced PSR and the temperature that produces it (pivotal temperature) are of limited use to guide climate mitigation management because an equal PSR may be demographically suboptimal. Here, I define population-advantageous primary sex ratios (PA-PSR) as the PSR that will tend to be in equilibrium in a population and that will result in balanced operational sex ratios; I then estimate PA-PSR for different reproductive frequencies (years elapsed between reproductive seasons) of adult female and male turtles. I also define population equilibrium temperature (PET) as the temperature that would result in the equilibrium PSR of hatchlings (i.e., PA-PSR). These concepts may help assess the influence of rising temperatures on populations, as they can better indicate if PSRs depart from those at equilibrium. I compared PA-PSR and beach PSR for two populations of sea turtles for which male and female remigration intervals were known and found that a mild or no feminization over the PA-PSR may be occurring. Because PSR varies inter-annually, and hatchlings coming from beaches of different thermal conditions could recruit to the same population, it is critical to estimate beach PSR at the right temporal and spatial scales. Climate mitigation strategies based on these concepts could provide better management guidance for conservation practitioners. Similar approaches could be considered for other female-biased species with temperature-dependent sex determination.

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“…While uncertainties persist in our understanding of the mechanisms that contribute to population productivity in response to increased feminization of sea turtles, there is increasing pressure to actively mitigate temperature increases on nesting beaches either by directly manipulating sex ratios (e.g., translocating nests) or indirectly by reducing nest temperatures with shading and watering (Fuentes et al, 2012;Jourdan and Fuentes, 2015;Blechschmidt et al, 2020;Lolavar and Wyneken, 2021;Patrício et al, 2021). Lowering the frequency of all female cohorts, increasing the frequency of strong male production years, or reducing the trend in mean sex ratio over time all have potential to delay a sex-ratio-mediated population decline.…”

Section: Introductionmentioning

confidence: 99%

A morphologist, a modeler, and an endocrinologist consider sea turtle sex ratios in a changing climate. Some wine was involved

Heppell

Wyneken²,

Heppell³

2022

Front. Ecol. Evol.

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Because the sex of sea turtles is determined by temperature during embryonic development, many populations are vulnerable to increased bias in primary sex ratios as global temperatures rise. Higher temperatures produce more females, and some populations are already showing years with all-female offspring production. But because sea turtles take decades to mature and have long adult lifespans, these primary sex ratio biases can take years to impact adult sex ratios, and the males from cohorts that are produced during cooler years may compensate for the sex ratio bias if they can breed more frequently and with multiple females. To date, little is known about male sea turtle reproductive behavior, making predictions of sex ratio skew impacts highly speculative. We used data from southern Florida loggerhead sea turtle nests to parameterize a simple population model to explore the effects of an increase in the proportion of female hatchlings over time on population trends, effective population size (Ne), and quasi-extinction probability. We also tested the effects of increasing the frequency of relatively high male production years to simulate potential mitigation strategies. While heuristic rather than predictive, our results expectedly show a rise in nest counts due to the increase in females over time, followed by population decline as males become limiting. Population collapse due to increased female bias will take many decades to occur, but sex ratio skew can have large impacts on Ne, and thus increase the potential for inbreeding. An increase in the frequency of male production years, even just one additional “good male year” per decade, can help mitigate these outcomes if the rate of feminization is not too rapid. Male breeding frequency and mating success are critical drivers of the results and must be prioritized for research.

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Effects of supplemental watering on loggerhead (Caretta caretta) nests and hatchlings

Cited by 13 publications

References 69 publications

Trialling seawater irrigation to combat the high nest temperature feminisation of green turtle Chelonia mydas hatchlings

Trialling seawater irrigation to combat the high nest temperature feminisation of green turtle Chelonia mydas hatchlings

When population-advantageous primary sex ratios are female-biased: changing concepts to facilitate climate change management in sea turtles

A morphologist, a modeler, and an endocrinologist consider sea turtle sex ratios in a changing climate. Some wine was involved

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