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

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 Archipelago, 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

Additional file 9 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 9: Table S9. Functional enrichment analysis results. Functional enrichment analysis results for contrasts between green turtle foraging aggregations

Additional file 8 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 8: Table S8. Differential gene expression analyses results for comparisons between green turtle foraging aggregations. Log fold change and adjusted p-values are listed for the California and Hawai’i, California and the Commonwealth of the Northern Mariana Islands (CNMI), and Hawai’i and CNMI Islands comparisons

Additional file 6 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 6: Table S6. Tissue-specific orthogroups. Orthogroups and the transcripts that belong to each orthogroup from each individual tissue-type leatherback transcriptome

Additional file 4 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 4: Table S4. Annotation and orthogroup information for leatherback multi-tissue transcriptome assembly transcripts. Transcripts that did not match to a Gene Ontology (GO) ID are not included

Additional file 1 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 1: Table S1. Sample metadata. Detailed metadata, raw read count, and the percent of reads that map to green (Chelonia mydas) turtle hemoglobin genes for each individual (n = 43) included in this study. Individuals without straight carapace length (SCL) denoted were not measured for these parameters

Additional file 11 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 11: Figure S2. Leatherback GO slim plots. Bar plots representing the number of genes in each Gene Ontology (GO) slim functional category from the multi-tissue (brain, lung, and ovary) leatherback turtle transcriptome

Additional file 5 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 5: Table S5. Species-specific orthogroups. Orthogroups and the transcripts that belong to each orthogroup from each species-specific blood transcriptome

Additional file 2 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 2: Table S2. Annotation and orthogroup information for green turtle blood transcriptome assembly transcripts. Transcripts that did not match to a Gene Ontology (GO) ID are not included

Additional file 3 of Species and population specific gene expression in blood transcriptomes of marine turtles

Additional file 3: Table S3. KEGG pathway analyses results. KEGG pathways for the green turtle transcriptome and the leatherback multi-tissue assembly