All seven species of turtles around the world have been reported to ingest microplastics (MPs), but their susceptibility to MPs is still unknown. Although studies on MP ingestion by turtles have taken place worldwide, only a few have investigated ingestion cases in the Northwestern Pacific Ocean. Sampling in such water basins is necessary to obtain a geographically comprehensive understanding of MP ingestion by turtles. Tokyo Bay, a Japanese bay facing the Pacific Ocean, is the gateway to the most industrialized region in Japan. The bay is highly polluted with MPs even compared to other bays in the world. The presence of rivers is one of the factors that drives MP pollution in ocean waters, but there is a critical knowledge gap regarding whether and how MP densities in the ocean influence the amount of MP ingestion by turtles. In this study, we investigated 22 bycaught/stranded turtles from inside and outside Tokyo Bay, where they faced high and low risks of MP exposure, respectively. We recorded the number of MPs inside their esophagi and stomachs, bycatch/stranding locations, and straight standard carapace length (SSCL). Sixty-five MP particles were isolated from 8 out of the 22 subject turtles (36.4%). The particles were composed of 8 polymer types: polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polypropylene (PP)/nylon compounds, styrene-butadiene rubber (SBR), cotton polystyrene, urea-formaldehyde (UF) resin, and unsaturated polyester (UP) resin. Thermoplastic (PE, PP, PET, and PP/nylon compounds) dominated the samples from the seven turtles in the high-risk areas, which was consistent with previous studies on MP properties in Tokyo Bay waters. Poisson regression, with the number of MPs and the bycatch/stranding locations as objective and explanatory variables, respectively, indicated that turtles in high-risk areas ingested significantly more MPs than those in low-risk areas. This result enhances our understanding of the dynamics of MPs in the environment. Inflows of MPs from major rivers influence pollution levels in the ocean, and contamination in local aquatic districts affects MP ingestion by wild turtles in that region.

Plastic ingestion is considered one of the main threats and a priority conservation concern for marine turtles. Understanding the impacts of plastic ingestion is crucial for assessing the vulnerability of marine turtles to this threat. The existing approaches for researching/monitoring plastic ingestion in marine turtles are numerous, and these essentially depend on (i) the source of specimens, dead animals (stranded and bycaught turtles) or live animals (turtles rescued from stranding or bycatch events and wild-captured turtles); and (ii) the sampling methods used to collect the ingested plastic (necropsy, fecal matter monitoring or gastric lavage). The aim of this study is to assess the strengths and limitations of these approaches based on a study of plastic ingestion by juvenile green turtles (N=237), Chelonia mydas, in Uruguayan waters from 2014 to 2020. The overall incidence of plastic ingestion was over 70% across all sources of specimens. All examined turtles exhibited a similar pattern of ingestion with respect to plastic characteristics; laminar soft plastics in clear/transparent and white colors were the most consumed type of plastic across all sources of specimens, accounting for 30% to 60% of the ingested plastic. However, the quantities of plastic registered on stranded dead turtles (mean ± SD = 260.1 ± 343.7 pieces of plastic) were at least 10 times greater in comparison to the other sources of specimens, also exhibiting a higher variability in terms of amounts and characteristics of plastic ingested. We conclude that stranded turtles (and potentially rescued turtles) collected opportunistically are subject to analysis biases because they may be in poor health conditions when encountered, consequently reflecting abnormal feeding behavior and/or habitat use. Nevertheless, these animals can provide valuable insights into the severity of plastic ingestion impacts on individual turtles. In contrast, bycaught and wild-captured turtles are generally more reliable indicators of a population's overall exposure to plastic ingestion if sampling is systematic over time. Regarding sampling methods, necropsy remains the most reliable technique, enabling the collection of all digestive contents separately from esophagus, stomach, and intestines. While faecal monitoring allows for the inclusion of live animals in this type of study, provided that the monitoring periods exceed the upper limit of ingestion passage time. Gastric lavages were found to be an inefficient method for collecting ingested plastic in this study.

Plastic pollution is steadily increasing and entering the oceans, with harmful effects on the environment and marine species through ingestion or entanglement. Once in the ocean, they accumulate in subtropical gyres known as "garbage patches". The North Pacific garbage patch is the largest and the one that has attracted the most attention. However, the garbage patch of the Indian Ocean, which could be the second largest according to predictive models, is less studied. For this reason, it is very important to provide a baseline for the abundance and characterization of plastic found in different compartments, such as the shoreline (beaches), ocean (sea surface/water column), deep sea and marine biota (bioindicator species).

In this case, we analyzed plastic debris ingested by loggerhead sea turtles (Caretta caretta) from longliner bycatches between 2007 and 2021 in the Southwest Indian Ocean (SWIO). Loggerheads were undertaken by the Kelonia sea turtle rehabilitation center on Reunion Island. We also studied plastic debris accumulated on 3 beaches of the east coast of Madagascar as a proxy for ocean plastics, in order to compare the characteristics of beached plastics and plastics ingested by turtles. More than 22,000 plastic debris were counted, measured, weighed, and sorted by category and color. Furthermore, we conducted a “brand audit” of the plastics to determine their country of origin. And an ocean circulation model was used to identify the most likely sources of plastics in the SWIO.

In total, 202 of the 266 loggerheads analyzed had ingested plastics. The frequency occurrence increased from 25% in 2007 to 78% in 2021. Mean average of plastic debris ingested was 56.83 ± 4.59 plastic debris per turtle. Plastics categorized as “hard” and “white” were equally dominant in loggerheads and on beaches and “selectivity tests” confirm that there is no selectivity in diet. Both the brand audit and circulation modeling demonstrated that Southeast Asia is the main source of plastic pollution in the region. The model highlighted a second origin from South Africa and a connection from maritime input between the Pacific and Indian Oceans.

This study demonstrates that loggerheads have a high rate of plastic ingestion, equivalent to the ingestion rate in the North Pacific and can be used as bioindicators of plastic pollution in the SWIO. Observations in situ, combined with dispersal models, can help to better understand the circulation and location of the garbage patch in the Indian Ocean. Additional research is needed to improve our understanding of the impact of plastic debris on loggerheads and on the environment (marine and terrestrial).

Marine vertebrates such as sea turtles are particularly susceptible to plastic pollution through ingestion or entanglement. Ingestion of plastic has been observed in all sea turtle species. In this study, 46 juvenile green sea turtles (Chelonia mydas) in two national parks (Galápagos and Machallilla) and a coastal bay in Mainland Ecuador were investigated to assess the prevalence of plastic in their feces and compared with a suite of health metrics (vital signs, hematology, and blood chemistry). Fourier transform infrared spectroscopy (FT-IR) revealed that sea turtles had x̄= 4.4±5.2 (range:0-19) microplastics (MPs)/g in feces. Furthermore, these levels differed according to sampling location, with the most polluted samples found in the Galápagos Marine Reserve (GMR). Fibers were the most common type, x̄=3.8±4.5 (range:0-16) MPs/g, and polyvinyl alcohol (PVOH), x̄=1.4±2.2 (range:0-10) MPs/g, and polyacrylates (PMMA) x̄= 0.95±1.3 (range:0-5) MPs/g, were the most common synthetic polymers identified by FT-IR. In tandem, we tested a complementary methodology for quantifying synthetic mass polymer concentrations within the same fecal matter: pressurized liquid extraction with double-shot pyrolysis-mass spectrometry gas chromatography (Pyr-GC/MS). This method detected polyethylene (PE) x̄= 367±1158 (range:0-6096) µg/g as the highest mass polymer concentration in feces, and polypropylene (PP) x̄= 155±434 (range:0-2944) µg/g was also abundant. The analysis also showed that the levels of plastics detected varied by location, with the most polluted samples being located in the GMR, but not in the same areas identified by FT-IR. We found that 98% of the sea turtles in our sample population had detectable levels of plastic pollution in their feces, as identified by both techniques: FT-IR detected 70% and Pyr-GC/MS detected 83%. The discrepancies in the prevalent type of synthetic polymer and the most polluted animals in our samples, as identified by both methods, raise questions regarding the reliability of these techniques in comprehending plastic pollution. Nonetheless, both techniques indicated that the animals in the GMR were more polluted in our study populations. Health metrics showed that the animals were clinically normal, based on vital signs, morphometry, and blood values. However, animals in protected areas are more polluted, raising concerns about their future health.

Sea turtles can be an imperative bioindicator for anthropogenic chemical pollution due to their long lifespans, extended intestine passage time, and high trophic position, facilitating the accumulation of these chemicals. Persistent organic pollutants (POPs) are synthetic chemicals with a potential for low environmental degradation rate, long-range transport, bioaccumulation, biomagnification, and harmful effects on living organisms. Plastic additives, such as stabilizers and antioxidants, are added to enhance plastic properties, and as they are not chemically bound to the polymer, they are readily leachable. They have been detected in marine environments and marine organisms as plastic pollution becomes increasingly severe. In South Korea, the incidence of sea turtle bycatch is rising, and turtles exhibit high plastic ingestion frequency and quantity. Since the growing significance of biomonitoring of sea turtles in this region, we investigated the levels of POPs and plastic additives in the liver of sea turtle carcasses from the Korean coast. A total of 44 sea turtles were subjected to POPs analysis, consisting of 27 loggerheads (Caretta caretta), 13 green turtles (Chelonia mydas), 3 leatherbacks (Dermochelys coriacea), and 1 hawksbill (Eretmochelys imbricata). Among these, 21 were targeted for plastic additive analysis (9 loggerheads and 12 greens). The targeted chemicals included PAHs, PCBs, organochlorine pesticides (DDTs, HCHs, CHLs, and HCB), PBDEs, HBCDs, antioxidants, phthalates, UV stabilizers, and tire additives. Overall, plastic additives exhibited higher levels than POPs, except for tire additives. Loggerheads accumulated significantly more POPs (including DDTs, HCHs, and PBDEs) than greens (Kruskal-Wallis Test, p < 0.05). The prevalence of POPs in loggerheads may be associated with their omnivorous diet, contrasting with the herbivorous diet of green turtles. Loggerheads and greens had similar isomeric (or congener) profiles of POPs except for PBDEs. Three-ring PAHs, hexa-PCBs, DDE, β-HCH, trans-nonachlor, and α-HBCD were dominant. Interestingly, greens accumulated higher levels of antioxidants, phthalates, and UV stabilizers than loggerheads, although not significantly (Kruskal-Wallis Test, p > 0.05). Greens also showed a higher accumulation of PAHs than loggerheads (Kruskal-Wallis Test, p < 0.05). This is a meaningful finding as green turtles ingested more plastic than loggerheads (Moon et al., 2022). Phthalates, especially DEHP and DBP, were major components of plastic additives in both species, followed by UVMC80 (UV stabilizer), 2,4-DTBP (antioxidant), and IPPD (tire additive). Their diets and plastic ingestion quantities could influence the interspecies difference in the accumulation profiles of POPs and plastic additives.

The Pacific Ocean supports two critically endangered leatherback sea turtle populations, both severely impacted from ongoing bycatch within small-scale and industrial fisheries. Conservation planning has included population viability analyses (PVA), which depend on accurate demographic inputs to yield realistic results for informing management decisions. PVA projections are based on the best available demographic data, which includes very limited data on small-scale fisheries bycatch, and has less than one percent observer coverage in industrial fisheries. As population recovery is dependent on reducing leatherback bycatch, it is critical that we know where, when, and how much bycatch is occuring. Here, we undertake a systematic review to aggregate existing estimates of leatherback bycatch within the Pacific Ocean for the purpose of creating the most contemporaneous and comprehensive estimate of Pacific leatherback bycatch. Searches through scientific databases and Google Scholar yielded 204 results which quantify bycatch for seven gear types in sixteen of the fifty countries fishing in the Pacific. New methods explore how much additional data can be captured with unprecedented literature review methods, such as searching in languages of all fishing countries, and using AI-translation of fishing reports for analysis. The final results will be presented to an expert elicitation group to determine certainty in literature estimates of bycatch, which will inform updated PVAs for both Pacific leatherback populations. Final PVA results will reveal the fisheries and countries that are most impacting the Pacific leatherbacks through their annual bycatch, and could help direct conservation efforts towards the most detrimental fisheries.

The Pacific waters of Panamá and Colombia are home to four species of sea turtles (leatherback, hawksbill, olive ridley, and green turtles). All these species are susceptible to injury or death due to their interactions with fisheries. The impact of fisheries bycatch on marine turtle populations is a product of a combination of fisheries features, such as fishing effort, gear and distribution, and biological factors like the life history of sea turtles (e.g., late maturity, long life span) and life-cycle traits (e.g., distinct ontogenetic habitats, separate breeding and feeding grounds). Fisheries bycatch is a particular challenge in developing countries because most fisheries are artisanal, and the relatively small size of the boats and lax management of the fishing activities makes it difficult to deploy observers. Panamá and Colombia are considered data-deficient regions regarding bycatch risks for sea turtles. We conducted a standardized port-based survey to provide accurate information on the magnitude and nature of bycatch and fishers' perception of management measures and laws for sustainable fisheries in a regional frame. Surveys were timed to coincide with peak fishing activity based on available government data. Between 2016 and 2019, we administered 966 comprehensive bycatch assessment surveys in 29 fishing ports (Panamá: n = 308 fishers, 17 ports; Colombia: n = 658, 12 ports). In Panamá and Colombia, bycatch events were more frequent when using hook gears (longline and hand line) and seine, and gillnet and hook gears, respectively. We used multinomial models to assess the relationship between the bycatch of the different turtle species and multiple fishing gears, seasons, and latitudes. We found the model that best fitted our data and explained the bycatch in the area includes fishing gear and latitude (Df = 1499, P = 3.0976E-64, AIC = 2790, Accuracy 0,64). Also, the posthoc analyses showed the variables gear (p<2.2e-16) and latitude (p<2.2e-16) were significant; however, there were no significant differences among the fishing gear types . Bycatch events were extrapolated across fishing fleets to estimate 7,885 marine turtles caught annually in Panamá, and 5,289 marine turtles caught annually in Colombia. Our results highlight the relevance of continuing work on bycatch mitigation programs in both countries. Our research is the first of its kind in Panamá and Colombia and will lay the groundwork for additional studies and outreach activities. It was also the first step to establishing contacts within artisanal fishing communities and forming collaborations with government fisheries agencies and the Ministries of Environment.