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Hydrocarbon (i.e. oil) extraction, transport, consumption, and pollution occur daily in marine environments, threatening vulnerable natural resources, habitats, and biodiversity. However, threats of episodic oil spills to imperiled marine species are not as well-studied as more acute, readily apparent threats such as incidental capture in fisheries and habitat degradation. We performed a global review of spill incident databases to evaluate reported effects of oil spills on sea turtles, which are flagship species of the world’s oceans. Our goals were to (1) summarize available information about oil spills and their effects on sea turtles; (2) identify major knowledge gaps; and (3) provide recommendations related to oil spills and sea turtles for managers, researchers, and conservation groups around the world. Over 2000 oil spill incidents of variable magnitude (range: ~20 to >1 million barrels) have occurred worldwide in the past 60 yr in areas where sea turtles are found, but resulting effects on sea turtles have been reported in less than 2% of those incidents. Further, evidence indicates that most effects are related to heavy external oiling, while chemical effects of oil exposure have not been well defined. We recommend that, where available, resources be prioritized to document co-occurrence of turtles and oil, the degree and nature of oil exposure, and mortality and reproductive losses to individual sea turtles and their populations caused by spills and spill response activities. These data will best inform assessments of the extent and magnitude of adverse effects of oil spills on sea turtles.

During the BP Deepwater Horizon (DWH) oil spill in 2010, 319 live oiled sea turtles were rescued and admitted to rehabilitation centers for decontamination and veterinary care. Most turtles were small, surfaceñpelagic juveniles that were collected from oiled habitat distant from shore. Serial hematology, plasma biochemistry, and blood gas analyses were reviewed to characterize abnormalities relative to observed degree of oiling. Clinicopathological abnormalities upon admission indicated acute, nonspecific metabolic and osmoregulatory derangements that were attributable to a combination of events including stress, exertion, physical exhaustion, and dehydration related to oiling, capture, and transport. Specific toxicological effects reported in other taxa were not observed. Initial point-of-care blood data from one rescue center were evaluated using clinical assessment of physiological status for all turtles of all species with available data for pH, pCO2, sodium, and potassium. In addition, a prognostic model that was specifically developed for cold-stunned Kempís ridley sea turtles Lepidochelys kempii was applied to oiled Kempís ridley turtles from one center. Thirty-six percent of oiled turtles were identified as physiologically deranged based on a clinical assessment of their physiological status, and 25% of oiled Kempís ridley sea turtles exceeded the mortality risk threshold of the prognostic model. These results indicate that the physiological derangements in these animals were relatively severe and clinically relevant. Based on observations during the DWH spill, adverse physiological effects in sea turtles may be an important consequence of stress, exertion, physical exhaustion, and dehydration secondary to oiling, capture, and transport.

The Deepwater Horizon (DWH) oil spill was unprecedented in extent and duration, and affected marine natural resources, including sea turtles, throughout the northern Gulf of Mexico. Consequently, US federal and state Trustees documented and quantified oil exposure and resulting injuries to sea turtles under the DWH Natural Resource Damage Assessment. At-sea rescue operations focused on surface-pelagic juvenile sea turtles, which were especially at risk to oil exposure within oceanic convergence zones, and provided direct observations of the degree that turtles in this young life stage were exposed to DWH oil. In contrast, locations of larger neritic juvenile and adult turtles were documented during aerial surveys, but because these turtles were not captured, their oiling status could not be directly evaluated. Both the rescue operations and aerial surveys were able to observe only a small fraction of sea turtles within the vast spill footprint. We developed a spatio-temporally explicit approach that used direct observations of oiled surface-pelagic juvenile sea turtles and satellite-derived surface oil distributions to statistically estimate the probabilities of oil exposure for all sea turtles that were present within the area of the DWH spill, but whose oiling status was unknown. Our results enabled an expansion of exposure and injury quantification across the entire DWH spill area and period. This approach was conceptually straightforward and used common geospatial and statistical techniques, making it applicable to other situations in which the full extent of oil exposure for marine natural resources must be estimated from an incomplete sample.

Documentation of exposure of threatened and endangered sea turtles to petroleum and dispersant released into the northern Gulf of Mexico (GoM) during the Deepwater Horizon (DWH) oil spill was a critical component of the Natural Resource Damage Assessment (NRDA) process. Substances collected from the skin of oiled and suspected oiled turtles were analyzed for petroleum hydrocarbons to determine oiling status and oil sources. Tissue, gastroenteric and bile samples from a subset of visibly oiled and unoiled turtles that died during the spill in 2010 and in 2011 were analyzed for evidence of internal exposure and absorption of polycyclic aromatic hydrocarbons (PAHs) and the dispersant component dioctyl sodium sulfosuccinate (DOSS). The volume of external oil collected from sea turtles was sufficient to confirm the presence of petroleum on 61% of turtles, and oil from the DWH spill was identified as the source in 97% of those turtles in which conclusive comparison was possible. Visibly oiled turtles had higher concentrations of tissue PAH or biliary fluorescent PAH metabolites compared to those determined in unoiled animals. Findings in most of the unoiled turtles were suggestive of low-level PAH exposure from various sources that may represent background values for sea turtles from the northern GoM. DOSS levels were below the limit of quantitation in all samples analyzed except in an esophagus sample of a heavily oiled sea turtle. Overall, the results for petroleum or petroleum-derived compounds of both external and internal samples of sea turtles supported visual observations of oiling.

The 2010 Deepwater Horizon (DWH) oil spill posed a severe threat to surface-pelagic sea turtles because the surface convergence zones, which provide vital habitat by aggregating pelagic Sargassum and other floating material, also aggregated floating oil. Following the DWH spill, turtle rescue operations between 17 May and 9 September 2010 documented 937 juvenile sea turtles in the spill area and examined 574 captured turtles. Of the captured turtles, 81% were visibly oiled. Transect searches in convergence zones found Kempís ridleys (51% of individuals), green turtles (37%), loggerheads (7%), hawksbills (2%), and unidentified sea turtles (2%). Line-transect methods estimated the density of all surface-pelagic sea turtles in surface convergence zones to be 3.32 km-2 (95% CI = 2.82ñ3.88), and the density of heavily oiled turtles to be 0.24 km-2 (95% CI = 0.15ñ0.39). Turtle densities and the areal extent of heavy oiling probability were used to estimate total number of turtles exposed to DWH oil. We estimate approximately 402000 surface-pelagic sea turtles were exposed, and of those, 54800 were likely to have been heavily oiled. Our estimates formed the basis of surface-pelagic juvenile sea turtle mortality estimates included in the DWH natural resource damage assessment.

Injuries inflicted by sharks are a frequent observation in stranded sea turtles. Sharks prey on live turtles and scavenge carcasses, which can create uncertainty as to the cause of stranding when sea turtles are found dead with shark-bite wounds. Consequently, attributing the cause of stranding to a shark attack based purely on the presence of the characteristic wounds can overestimate predation by sharks as a cause of mortality. To better characterize the timing of shark-bite wounds relative to death of sea turtles in the southeastern USA, we performed necropsies on 70 stranded turtles that were found dead in which the predominant observation was bite wounds without any grossly evident vital responses (inflammation or healing). Postmortem examination included assessment for evidence of exsanguination and histopathological evaluation of skeletal muscle comprising wound margins. We characterized wounds as antemortem, perimortem, or postmortem based on specific criteria related to the presence or absence of supravital and intravital responses. Most (80%) shark-bite wounds were postmortem, 10% were antemortem, and 10% were perimortem. We found that antemortem and postmortem wounds were similar in extent and location except for wounds that primarily involved the shell, which were never found in cases of scavenging. For sea turtles found dead in the southeastern USA, our findings suggest that most shark-bite wounds without externally evident vital responses are due to scavenging. Additionally, this scavenging can significantly damage a carcass, potentially obscuring the detection of other causes of mortality. These findings should be considered when using data derived from stranded sea turtles to conduct mortality assessments.

Decompression sickness (DCS) has been described mainly in loggerhead turtles Caretta caretta bycaught in trawls and gillnets. Here we present cases of gas emboli (GE) in 8 green turtles Chelonia mydas and 2 Kemp's ridleys Lepidochelys kempii entrained in hopper dredges that were working at 8.8-15.2 m depths during shipping channel maintenance or beach renourishment activities. Turtle weights ranged from 2.2 to 6.7 kg. All were found alive with blunt force injuries from passage through the dredge and were taken to rehabilitation facilities. Four green turtles died or were euthanized within 24 h. Six turtles survived. Radiographic or ultrasonographic evidence of GE was detected in 4 turtles, including 3 mortalities. Computed tomography (CT) revealed perirenal and cervical GE in 4 turtles, including 1 mortality. No GE were detected in 2 of the survivors. Upon necropsy, GE were found in mesenteric vessels, the right atrium, and kidneys. Histopathology confirmed that tissues were in a good state of preservation without evidence of bacterial overgrowth or putrefactive gas formation. Death likely resulted primarily from massive tissue trauma from the dredge, but moderate GE could have led to DCS and complicated recovery. The surviving turtles weighed less than those that did not survive. Besides hypothesized stress/exercise-induced circulatory changes of blood through the lungs and pressure reduction of forced surfacing from depth, drastic pressure change within the dredge pipes before and after the pump could contribute to GE. Hopper dredge entrainment is an additional cause of GE and potential DCS in sea turtles.

Data on Karenia brevis red tides (≥105 cells l-1) and on dead or debilitated (i.e. stranded) Kemp's ridleys Lepidochelys kempii, loggerheads Caretta caretta, green turtles Chelonia mydas, hawksbills Eretmochelys imbricata, and leatherbacks Dermochelys coriacea documented in Florida during 1986-2013 were evaluated to assess red tides as a sea turtle mortality factor. Unusually large numbers of stranded sea turtles were found coincident with red tides primarily along Florida's Gulf coast but also along a portion of Florida's Atlantic coast. These strandings were mainly adult and large immature loggerheads and Kemp's ridleys, and small immature green turtles and hawksbills. Unusually large numbers of stranded leatherbacks never coincided with red tide. For the 3 most common species, results of stranding data modeling, and of investigations that included determining brevetoxin concentrations in samples collected from stranded turtles, all indicated that red tides were associated with greater and more frequent increases in the numbers of stranded loggerheads and Kemp's ridleys than in the number of stranded green turtles. The mean annual number of stranded sea turtles attributed to K. brevis red tide was 80 (SE = 21.6, range = 2-338). Considering typical stranding probabilities, the overall mortality was probably 5-10 times greater. Red tide accounted for a substantial portion of all stranded loggerheads (7.1%) and Kemp's ridleys (17.7%), and a smaller portion of all stranded green turtles (1.6%). Even though K. brevis red tides occur naturally, the mortality they cause needs to be considered when managing these threatened and endangered species.

Five green (Chelonia mydas) and 11 Kemp's ridley (Lepidochelys kempii) sea turtles found dead, or that died soon after stranding, on the southern Texas (USA) coast during 2 Karenia brevis blooms (October 2015, September-October 2016) were tested for exposure to brevetoxins (PbTx). Tissues (liver, kidney) and digesta (stomach and intestinal contents) were analyzed by ELISA. Three green turtles found alive during the 2015 event and 2 Kemp's ridley turtles found alive during the 2016 event exhibited signs of PbTx exposure, including lethargy and/or convulsions of the head and neck. PbTx were detected in 1 or more tissues or digesta in all 16 stranded turtles. Detected PbTx concentrations ranged from 2 to >2000 ng g-1. Necropsy examination and results of PbTx analysis indicated that 10 of the Kemp's ridleys and 2 of the green turtles died from brevetoxicosis via ingestion. This is the first documentation of sea turtle mortality in Texas attributed to brevetoxicosis.

Three wild immature green sea turtles Chelonia mydas were found alive but lethargic on the shores of the Indian River Lagoon and Gulf of Mexico in Florida, USA, and subsequently died. Necropsy findings in all 3 turtles included partial occlusion of the trachea by a mass comprised of granulomatous inflammation. Pigmented fungal hyphae were observed within the lesion by histology and were characterized by culture and sequencing of the internal transcribed spacer 2 domain of the rRNA gene and D1/D2 region of the fungal 28s gene. The dematiaceous fungus species Veronaea botryosa was isolated from the tracheal mass in 2 cases, and genetic sequence of V. botryosa was detected by polymerase chain reaction in all 3 cases. Genetic sequencing and fungal cultures also detected other dematiaceous fungi, including a Cladosporium sp., an Ochroconis sp., and a Cochliobolus sp. These cases are the first report of phaeohyphomycosis caused by V. botryosa in wild marine animals.

Spirorchiid trematodes are implicated as an important cause of stranding and mortality in sea turtles worldwide. However, the impact of these parasites on sea turtle health is poorly understood due to biases in study populations and limited or missing data for some host species and regions, including the southeastern United States. We examined necropsy findings and parasitological data from 89 loggerhead Caretta caretta and 59 green turtles Chelonia mydas that were found dead or moribund (i.e. stranded) in Florida (USA) and evaluated the role of spirorchiidiasis in the cause of death. High prevalence of infection in the stranding population was observed, and most infections were regarded as incidental to the cause of death. Spirorchiidiasis was causal or contributory to death in some cases; however, notable host injury and/or large numbers of parasites were observed in some animals, including nutritionally robust turtles, with no apparent relationship to cause of death. New spirorchiid species records for the region were documented and identified genera included Neospirorchis, Hapalotrema, Carettacola, and Learedius. Parasites inhabited and were associated with injury and inflammation in a variety of anatomic locations, including large arteries, the central nervous system, endocrine organs, and the gastrointestinal tract. These findings provide essential information on the diversity of spirorchiids found in Florida sea turtles, as well as prevalence of infection and the spectrum of associated pathological lesions. Several areas of needed study are identified with regard to potential health implications in the turtle host, and findings caution against over-interpretation in individual cases.

Eighteen green turtles Chelonia mydas recovered from the Atlantic and Gulf coasts of Florida and Tortuguero National Park, Costa Rica, were diagnosed with renal oxalosis by histopathological examination. Affected sea turtles included 14 adults and 4 immature animals, which comprised 26% (18/69) of green turtle necropsy cases available for review. Calcium oxalate deposition ranged from small to moderate amounts and was associated with granuloma formation and destruction of renal tubules. All affected turtles died from traumatic events or health problems unrelated to renal oxalosis; however, 1 immature turtle had notable associated renal injury. Crystal composition was confirmed by infrared and scanning electron microscopy and energy dispersive X-ray analysis. The source of calcium oxalate is unknown and is presumed to be of dietary origin.

Beginning in October 2000, subadult loggerhead sea turtles Caretta caretta showing clinical signs of a neurological disorder were found in waters off south Florida, USA. Histopathology indicated generalized and neurologic spirorchiidiasis. In loggerhead sea turtles (LST) with neurospirorchiidiasis, adult trematodes were found in the meninges of the brain and spinal cord of 7 and 3 affected turtles respectively, and multiple encephalic intravascular or perivascular eggs were associated with granulomatous or mixed leukocytic inflammation, vasculitis, edema, axonal degeneration and occasional necrosis. Adult spirorchiids were dissected from meningeal vessels of 2 of 11 LST brains and 1 of 10 spinal cords and were identified as Neospirorchis sp. Affected LST were evaluated for brevetoxins, ciguatoxins, saxitoxins, domoic acid and palytoxin. While tissues from 7 of 20 LST tested positive for brevetoxins, the levels were not considered to be in a range causing acute toxicosis. No known natural (algal blooms) or anthropogenic (pollutant spills) stressors co-occurred with the turtle mortality. While heavy metal toxicosis and organophosphate toxicosis were also investigated as possible causes, there was no evidence for their involvement. We speculate that the clinical signs and pathologic changes seen in the affected LST resulted from combined heavy spirorchiid parasitism and possible chronic exposure to a novel toxin present in the diet of LST.