Conservation importance of previously undescribed abundance trends: increase in loggerhead turtle numbers nesting on an Atlantic island

1. The impacts of anthropogenic climate change will be most dramatic for species that live in narrow thermal niches, such as reptiles. Given the imminent threat to biodiversity, and that actions to reduce carbon emissions are not yet sufficient, it is important that a sound evidence base of potential mitigation options is available for conservation managers.2. Successful incubation and production of male sea turtle hatchlings is threatened by increased global temperatures (sex is determined by the temperature at which eggs incubate). Here we test two conservation tools to reduce incubation temperatures: clutch splitting and clutch shading, on a nesting loggerhead turtle Caretta caretta population in the Eastern Atlantic Ocean.3. During the thermosensitive period of incubation, split and shaded clutches were both 1.00°C cooler than control nests. Clutch splitting (mean: 45 eggs) reduced nest temperatures by reducing metabolic heating during incubation compared to controls (mean: 92 eggs). Modelled primary sex ratios differed between nest treatments, with 1.50% (±6% SE) females produced in shaded nests, 45.00% (±7% SE) females in split nests and 69.00% (±6% SE) females in controls. Neither treatment affected hatchling size, success, mass or vigour. When clutch splitting was repeated 2 years later, hatch success was higher in split clutches compared to controls. 4. Synthesis and applications. Clutch splitting and clutch shading successfully altered the thermal profile of incubating turtle nests. When there is sufficient knowledge to better understand the effects of intervention on fundamental population demographics, they will be useful for reducing incubation temperatures in sea turtle nests, potentially increasing nest survival and male hatchling production. The effect of clutch splitting in reducing nest temperature was lower relative to clutch shading, but requires significantly less funding, materials and specialist skill, key factors for management of turtle rookeries that are often in remote, resource-limited areas.

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“…Around 65% of nests in this population are laid on the island of Boa Vista (Laloë et al, 2019; Figure 1).…”

Section: Study Areamentioning

confidence: 97%

“…The study took place on the island of Boa Vista, Cabo Verde, West Africa, the world's second largest nesting aggregation of loggerhead sea turtles Caretta caretta (Laloë et al, 2019;Marco et al, 2012).…”

Section: Study Areamentioning

confidence: 99%

Low‐cost tools mitigate climate change during reproduction in an endangered marine ectotherm

Clarke

Elliot

Abella-Perez

et al. 2021

Journal of Applied Ecology

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“…The increase in loggerhead turtle nesting numbers suggests that if threats to adult turtles are ameliorated, small populations can recover-and indeed, an absence of Allee effects has been noted in the Cayman Islands and in other nesting populations (Bell et al, 2010;Mazaris et al, 2017). A reduction of wild sea turtle harvesting is also thought to have played an important role in the increase in loggerhead turtle nest numbers in Cape Verde (Marco et al, 2012), which showed a 15-fold increase over a 10-year period (2008-2017) (Laloë et al, 2020). However, wider environmental factors also likely influence these trends; between 1999 and 2007, the same period where there was no increase in loggerhead nests in the Cayman Islands, growth rates of Northwest Atlantic loggerhead turtles declined significantly (Bjorndal et al, 2013).…”

Section: Loggerhead Population Trendmentioning

confidence: 99%

Cayman Islands Sea Turtle Nesting Population Increases Over 22 Years of Monitoring

et al. 2021

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Given differing trajectories of sea turtle populations worldwide, there is a need to assess and report long-term population trends and determine which conservation strategies are effective. In this study, we report on sea turtle nest monitoring in the Cayman Islands over a 22-year period. We found that green (Chelonia mydas) and loggerhead (Caretta caretta) nest numbers increased significantly across the three islands since monitoring began in 1998, but that hawksbill nest numbers remained low with a maximum of 13 nests recorded in a season. Comparing the first 5 years of nest numbers to the most recent 5 years, the greatest percentage increase in green turtle nests was in Grand Cayman from 82 to 1,005 nests (1,126%), whereas the greatest percentage increase for loggerhead turtle nests was in Little Cayman from 10 to 290 nests (3,800%). A captive breeding operation contributed to the increase in the Grand Cayman green turtle population, however, loggerhead turtles were never captive-bred, and these populations began to increase after a legal traditional turtle fishery became inactive in 2008. Although both species have shown significant signs of recovery, populations remain at a fragment of their historical level and are vulnerable to threats. Illegal harvesting occurs to this day, with multiple females taken from nesting beaches each year. For nests and hatchlings, threats include artificial lighting on nesting beaches, causing hatchlings to misorient away from the sea, and inundation of nests by seawater reducing hatch success. The impacts of lighting were found to increase over the monitoring period. Spatial data on nest distribution was used to identify critical nesting habitat for green and loggerhead turtles and is used by the Cayman Islands Department of Environment to facilitate remediation of threats related to beachside development and for targeted future management efforts.

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“…Recent data shows that this loggerhead subpopulation might be the largest population of this species worldwide [3,4]. Furthermore, after the Island of Boavista, the shores of the Island of Maio are, together with the Island of Sal, the most important nesting sites in the archipelago [5,6].…”

Section: Introductionmentioning

confidence: 99%

Antibiotic Resistance and Virulence Profiles of Gram-Negative Bacteria Isolated from Loggerhead Sea Turtles (Caretta Caretta) of the Island of Maio, Cape Verde

Fernandes

Grilo

Cunha

et al. 2021

Preprint

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Background: Several studies detected high levels of antibiotic-resistance in loggerhead sea turtles (Caretta caretta) and pointed this species as prime reservoirs of antibiotic-resistant bacteria and carriers of potentially pathogenic bacteria. This study aimed to characterize, for the ﬁrst time, the Gram-negative aerobic microbiota of the Cape Verdean loggerhead subpopulation. Cloacal, oral and egg content swab samples from 33 nesting loggerheads (n = 99) of the Island of Maio were analysed regarding the presence of Gram-negative bacteria and their antibiotic resistance and virulence proﬁles. Results: Shewanella putrefaciens (27.78%), Morganella morganii (22.22%) and Vibrio alginolyticus (22.22%) were the most prevalent species isolated from the animals under study. A low incidence of antibiotic-resistant bacteria (26%) was detected, and no multidrug-resistant isolates were identiﬁed. Non-Enterobacteriaceae isolates presented the most complex virulence proﬁles, revealing the ability to produce hemolysins (100%), DNases (89%), lipases (79%), proteases (53%), lecithinases (21%), gelatinases (16%), and also bioﬁlms (74%). Moreover, higher virulence indices were obtained for turtles with high parasite intensities compared with apparently healthy animals, and a positive correlation between antibiotic resistance and virulence was observed. Conclusions: Results suggest that this loggerhead population may be less exposed to antimicrobial compounds, probably due to the low anthropogenic impact observed in both their nesting (the Island of Maio) and foraging sites. Nevertheless, the presence of potentially pathogenic bacteria expressing virulence factors may threat both sea turtles’ and humans’ health.

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Conservation importance of previously undescribed abundance trends: increase in loggerhead turtle numbers nesting on an Atlantic island

Cited by 22 publications

References 31 publications

Low‐cost tools mitigate climate change during reproduction in an endangered marine ectotherm

Low‐cost tools mitigate climate change during reproduction in an endangered marine ectotherm

Cayman Islands Sea Turtle Nesting Population Increases Over 22 Years of Monitoring

Antibiotic Resistance and Virulence Profiles of Gram-Negative Bacteria Isolated from Loggerhead Sea Turtles (Caretta Caretta) of the Island of Maio, Cape Verde

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