Quarter-Century (1993–2018) Nesting Trends in the Peripheral Populations of Three Sea Turtle Species at Ishigakijima Island, Japan

Okuyama, Junichi; Ishii, Hisakazu; Tanizaki, Shigeo; Suzuki, Tomoko; Abe, Osamu; Nishizawa, Hideaki; Yano, Aya; Tsujimura, Masako; Ishigaki, Takakazu; Ishigaki, Takashi; Kobayashi, Masahiro; Yanagida, Hirotaka

doi:10.2744/ccb-1428.1

Cited by 9 publications

(12 citation statements)

References 33 publications

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“…Therefore, to assess the trend of foraging dichotomy in the entire nesting area of Japan, we chose three other nesting sites in this study to represent the geographic nesting regions of Japan; Ishigaki Island, Okinoerabu Island and Ichinomiya (Figure 1a). Ishigaki Island is the geographic southern limit of nesting sites in the North Pacific loggerhead population (Okuyama et al, 2020), while Ichinomiya is the northern limit. Okinoerabu Island is located between the Yakushima and Ishigaki Islands.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, we collected the eggs only from the nests that occurred within 8 days on a beach in each year to avoid sampling the eggs from the same female, based on the fact that the inter‐nesting interval of females varied between 9 and 14 days on Ishigaki Island (Okuyama et al, 2020). The data on SCL of nesting females were obtained from the results of a previous nesting survey during 2003–2013 (Okuyama et al, 2020).…”

Section: Methodsmentioning

confidence: 99%

“…On the southernmost site Ishigaki Island, regular surveys for nesting have been conducted since 1993 (Okuyama et al, 2020).…”

Section: Nesting Surveymentioning

confidence: 99%

“…Over the last three decades, loggerhead nesting populations in Japan have shown a rapid decline in the 1990s, followed by a trend of gradual recovery (Biodiversity Center of Japan & Ministry of the Environment, 2016; Kamezaki et al, 2003). Casale and Matsuzawa (2015) 2016,2020), such as Omaezaki (Omaezaki city, 2020), Yakushima (Martin et al, 2020), Okinoerabu (Y. Yamashita personal communication) and Ishigaki Islands (Okuyama et al, 2020). Therefore, immediate conservation action for nesting populations is needed for the sustainable management of the North Pacific population.…”

Section: Introductionmentioning

confidence: 99%

“…Casale and Matsuzawa (2015) estimated that the number of adult females was approximately 8,100 in the North Pacific populations based on nest count data from 2009 to 2013. Since 2013, however, it has drastically reduced again with several nesting beaches attaining the lowest numbers of nesting individuals in 2019 (Biodiversity Center of Japan & Ministry of the Environment, 2016, 2020), such as Omaezaki (Omaezaki city, 2020), Yakushima (Martin et al, 2020), Okinoerabu (Y. Yamashita personal communication) and Ishigaki Islands (Okuyama et al, 2020). Therefore, immediate conservation action for nesting populations is needed for the sustainable management of the North Pacific population.…”

Section: Introductionmentioning

confidence: 99%

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Latitudinal cline in the foraging dichotomy of loggerhead sea turtles reveals the importance of East China Sea for priority conservation

Okuyama¹,

Watabe

Takuma

et al. 2022

Diversity and Distributions

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Aim: Quantifying the importance of habitat areas for conservation of highly migratory marine species with complex life histories can be challenging. For example loggerhead turtles (Caretta caretta) nesting in Japan forage both oceanically and neritically after their reproductive period. Here, we aimed to quantify the proportions of turtles using these two contrasting habitats (foraging dichotomy) to suggest priority conservation areas.Location: North Pacific Ocean. Methods:We examined the occurrence of foraging dichotomy at three nesting sites (Ishigaki, Okinoerabu Islands and Ichinomiya) based on stable isotope analysis of the egg yolks for 82 turtles and satellite tracking of post-nesting migration for 12 turtles.Moreover, we used the data of three other sites from previous studies (Yakushima Island, Minabe and Omaezaki).Results: Two neritic foraging grounds (East China Sea and the coastal area of the Japanese archipelago), and an oceanic ground (North Pacific Ocean) were identified.We found a latitudinal cline with respect to the occurrence of foraging dichotomy; >84% of the females nesting at southern sites (Ishigaki and Okinoerabu Islands), 73% at middle sites (Yakushima Island and Minabe) and <46% at northern sites (Omaezaki and Ichinomiya) were neritic foragers; the proportion of oceanic foragers increased at northern sites. Based on the annual number of nests in the entire nesting region of Japan, satellite tracking and the latitudinal cline of foraging dichotomy, we estimated that 70% and 9% of annual nesting females in Japan utilize the neritic foraging habitat in the East China Sea and the coastal area of the Japanese archipelago, respectively, and that and 22% utilize the oceanic habitat of the North Pacific Ocean. Main conclusions:The East China Sea represents a critical foraging habitat for the North Pacific populations of endangered loggerhead sea turtles. Our findings emphasize the need for international management to ensure their protection.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…On the southernmost site Ishigaki Island, regular surveys for nesting have been conducted since 1993 (Okuyama et al, 2020).…”

Section: Nesting Surveymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Latitudinal cline in the foraging dichotomy of loggerhead sea turtles reveals the importance of East China Sea for priority conservation

Okuyama¹,

Watabe

Takuma

et al. 2022

Diversity and Distributions

Self Cite

View full text Add to dashboard Cite

show abstract

Inter-annual variability in breeding census data across species and regions

2022

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There is an intense interest in long-term trends of species abundance that may reflect, for example, climate change or conservation actions. Less well studied are patterns in the magnitude of inter-annual variability in abundance across large spatial scales. We collated abundance time-series for 133 nesting sites across the globe of the seven sea turtle species. Inter-annual variability in nest numbers was lowest in loggerhead turtles (Caretta caretta), Kemp’s ridley (Lepidochelys kempii) and flatback turtle (Natator depressus) and highest in green turtles (Chelonia mydas), likely reflecting their lower trophic position compared to other species and hence tighter coupling of food availability to environmental conditions each year. The annual number of nests in green turtles could vary by 60-fold between successive years. We identified regional patterns in the magnitude of inter-annual variability in green turtle nest numbers, variability being highest for nesting beaches around Australia and lowest in the western Indian Ocean and equatorial Atlantic. These regional patterns are likely linked to corresponding patterns of environmental variability with, for example, areas subjected environmental extremes as part of the El Nino Southern Oscillation (ENSO) showing high inter-annual variability in nest numbers.

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Utility of carapace images for long-term photographic identification of nesting green turtles

Tabuki

Nishizawa

Abe

et al. 2021

Journal of Experimental Marine Biology and Ecology

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Quarter-Century (1993–2018) Nesting Trends in the Peripheral Populations of Three Sea Turtle Species at Ishigakijima Island, Japan

Cited by 9 publications

References 33 publications

Latitudinal cline in the foraging dichotomy of loggerhead sea turtles reveals the importance of East China Sea for priority conservation

Latitudinal cline in the foraging dichotomy of loggerhead sea turtles reveals the importance of East China Sea for priority conservation

Inter-annual variability in breeding census data across species and regions

Utility of carapace images for long-term photographic identification of nesting green turtles

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