Endangered Green Turtles (Chelonia mydas) of the Northern Mariana Islands: Nesting Ecology, Poaching, and Climate Concerns

Abstract

Marine turtles in the western Pacific remain threatened by anthropogenic impacts, but the region lacks long-term biological data for assessing conservation status and trends. The Central West Pacific (CWP) population of green turtles (Chelonia mydas) was listed as Endangered by the U.S. in 2016, highlighting a need to fill existing data gaps. This study focuses on the subset of this population nesting in the Commonwealth of the Northern Mariana Islands (CNMI). Using 11 years of nesting data, we (i) estimate reproductive demographic parameters, (ii) quantify abundance and trends, and (iii) estimate the impacts of anthropogenic threats, such as poaching of nesting females and increasing sand temperatures. In 2006-2016, nesting beach surveys, identification tagging, and nest excavations were conducted on Saipan, and rapid assessments of nesting activity were conducted on Tinian and Rota. On Saipan, temperature data-loggers were deployed inside nests and evidence of poaching (adults and eggs) was recorded. This study documents year-round nesting with a peak in March-July. Nester abundance for the three islands combined was 11.9 ± 5.7 (mean ± standard deviation) females annually, with at least 62.8 ± 35.1 nests observed per year. For 39 tagged individuals, straight carapace length was 95.6 ± 4.5 cm, remigration interval was 4.6 ± 1.3 years, and somatic growth was 0.3 ± 0.2 cm/yr. Reproductive parameter estimates included clutch frequency of 7.0 ± 1.3 nests per female, inter-nesting interval of 11.4 ± 1.0 days, clutch size of 93.5 ± 21.4 eggs, incubation period of 56.7 ± 6.4 days, hatching success of 77.9 ± 27.0%, and emergence success of 69.6 ± 30.3%. Mean nest temperature of 30.9 ± 1.5 • C was above the pivotal threshold of 29.0 • C for temperature dependent sex determination, suggesting a female bias may already exist. Model results suggest (i) hatching success decreases and embryonic death increases when nests experience maximum temperatures beyond 34.4 • C and 33.8 • C, respectively, and (ii) embryonic death increases in nests with mean temperatures beyond 31.1 • C. On Saipan, 32% of nesters were poached, reducing the annual population growth rate from 11.4 to 7.4%. This study provides the first comprehensive assessment of a nesting green turtle population in the Mariana Summers et al. Nesting Ecology of Micronesian Green TurtlesArchipelago, as well as Micronesia, providing baseline data for the endangered CWP population. Our reproductive demographic data, abundance trends, and anthropogenic threat impact analyses are critical for endangered species management, including assessments of population status and fisheries impacts.

Investigating the reproductive behaviour of the green sea turtle (Chelonia mydas) using parentage analysis

“…The true number is likely to lie between these two estimations and is coherent with clutch frequencies for other green turtle populations in the Pacific Ocean (reviewed in Pilcher 2021). They vary from 1.8 in French Frigate Shoal to 7 +-1.3 clutches per female per season in the Northern Mariana Islands (Balazs, 1980;Summers et al, 2018). Additionally, through parentage analysis, 74 nests without observed females in the field were associated with a female, demonstrating the efficiency of the analysis to supplement field observations.…”

Challenges in the impact evaluation of behaviour change interventions: The case of sea turtle meat and eggs in São Tomé

“…It is also comparatively easy to detect poaching activity for adult sea turtles. Their large size means they need to be dragged away rather than carried, leaving evident marks in the sand that can be spotted during daily beach patrols, regardless of weather conditions (Lino et al., 2010; Summers et al., 2018; Troëng & González, 1998).…”

eDNA metabarcoding for diet analyses of green sea turtles (Chelonia mydas)

“…The seven species of sea turtles are threatened by human exploitation and environmental change and are included in the IUCN Red list as critically endangered, endangered, vulnerable or data deficient. Despite the recovery of some major populations in the last decade following conservation efforts (Mazaris et al 2017), many populations continue to face large-scale anthropogenic threats, namely degradation and loss of nesting and feeding habitats, incidental capture in fisheries, direct harvesting, plastic ingestion and climate change (Santidrián-Tomillo et al 2015;Casale and Heppell 2016;Nelms et al 2016;Summers et al 2018;Patrício et al 2021). Accumulated evidence emphasizes the importance of adopting conservation actions to protect key habitats such as nesting beaches and feeding grounds (Wallace et al 2011;Godley et al 2020).…”