Lesson to Learn from an Endangered Green Turtle (Chelonia mydas): Marine Debris Ingestion, Rehabilitation and Satellite Tracking

Recent studies show that marine debris ingestion by sea turtles is rising (Schuyler et al., 2014). Green turtles (Chelonia mydas) brought in for rehabilitation allows an opportunity to provide insights into the possible effects of anthropogenic debris on animal’s survivorship during recovery and rehabilitation (Hoarau et al., 2014). Hematology and biochemical parameters, as measured in peripheral blood, are a useful diagnostic tool in animal health management (Barkakati et al., 2015; Li et al., 2015; Ramulu et al., 2015; Yaqub et al., 2018; Abdullah et al., 2020). Here, we present and discuss a rehabilitation case of buoyancy disorder occurring in a green sea turtle, which resulted from fishing activities and marine debris ingestion.

Turtle rehabilitation
 
A 32.76-kg green turtle C. mydas of curved carapace length 65.1 cm was bycaught in fishing gear near the Sicao of Tainan (23°00’39.1N, 120°08’27.1E) in south-western Taiwan in January 2016. The green turtle was rescued and entrusted to the National Museum of Marine Biology and Aquarium (NMMBA) for medical care. The turtle was rehabilitated, given appropriate treatment (included physical examination, evaluation of swimming activity, food ingestion, weight, core body temperature and blood sample analysis) and kept under observation in isolation for three months. When the turtle was initially taken into rehabilitation, exhibited conditions of poor appetite and positive buoyancy (Fig 1) due to weakness. Based on a physical examination, the turtle was in good body condition. A series of blood gas, blood biochemical and hematology parameters profiling was performed. The blood gas values included potential hydrogen (pH), partial pressure of carbon dioxide (pCO₂), partial pressure of oxygen (pO₂), base excess in extracellular fluid (BEecf), bicarbonate (HCO₃-), total carbon dioxide (TCO₂), saturated oxygen (sO₂), ionized calcium (iCa), potassium (K), sodium (Na), glucose (Glu) and creatinine (CRE). Biochemistry profiles included total protein (TP), albumin (ALB), total bilirubin (TBIL), aspartate aminotransferase (AST), alanine aminotransferase (ALT), alalkaline phosphatase (ALP), γ-glutamyltranspeptidase (GGT), creatinine kinase (CK), lactate dedehydrogenase (LDH), cholesterol (CHOL), triglyceride (TRI), glucose (GLU), blood urea nitrogen (BUN), uric acid (UA), phosphorus (PHOS), calcium (CA) and magnesium (MG). Hematological examinations included quantitative analysis of hemoglobin (HB), white blood cell (WBC) and packed cell volume (PCV).


 
Satellite tracking
 
After a 3-month recovery, the turtle was physically fit for release. Prior to the release, the turtle was tagged with Inconel tags on its fore- and/ or hind-limbs and microchip for identification (Balazs, 1999). The satellite tracking work was permitted under the protected wildlife use permissions of Forestry Bureau, Council of Agriculture, Executive Yuan, Taiwan (1051700373). A satellite Argos-linked transmitter was also attached to its carapace with fiberglass resin following the protocol as described by Balazs et al., (1996). The weight of the transmitter package was less than 5% of the body weight of the turtles to minimize potential impact to their health (Watson and Granger, 1998; Ng et al., 2018a). The turtle was successfully released with a satellite transmitter at Haikou Beach (22°05´28N, 120°42´52E ) in southern Taiwan on March 31, 2016. Satellite track of the oceanic movement was plotted using the basemap at Google Earth (Maptool (SEATURTLE.ORG, Inc.; http://www.seaturtle.org/maptool/) primarily with positional Argos data derived from the more accurate Location Class (LC) 1 to 3 signals; large spatial gaps were filled using data points of LC 0, A and B where appropriate following visual filtering for obviously inaccurate points (Chan et al., 2003; Parker et al., 2009), on the basis of excluding biologically unreasonable results of location points, including travel speed (>5 km/hr), points located on land and a turn of greater than 90 degrees in less than a 24-hour period (Parker et al., 2009). A maximum of one fix per day was selected with the highest accuracy LC and if more than one fix had this LC, the one closest to midday was selected (Casale et al., 2012; Parker et al., 2009). The end of a track was determined either by the last Argos position or when positional locations aggregated at a specific area ‘near shore’ if the turtle settled in areas along the open coast generally for approximately one month, implying that the tracked turtle had arrived and settled down at its foraging ground (Parker et al., 2009).

Results of metabolic parameters indicated an elevation in pO2 (mmHg) at 37°C, temperature corrected pO₂ and TCO₂; all other values (included PCV) were within the reference interval (Aguirre and Balazs, 2000; Anderson et al., 2011; Bolten and Bjorndal, 1992; Lewbart et al., 2014; Hamann et al., 2006; Phillips et al., 2015). Two days after intake, buoyancy of turtle improved as it was able to submerge. Within 3 to 26 days of rehabilitation, debris were found in turtle feces or floating at the surface of basins. The debris included fishing line, hard plastic, soft plastic, rope, wood and styrofoam (Fig 2 and Fig 3). After release on March 31, 2016 (Fig 4), during the 81-day satellite tracking, the turtle moved northward and reached Xiao Liu Chiu Island, where foraging green turtles are found around the Island waters harboring coral reef (Doo et al., 2012) and seaweed (Chang and Tseng, 2010) communities. The turtle stayed around Xiao Liu Chiu Island for 5 days and then moved southward back towards its release spot. The turtle remained residing in waters off Hengchun of southern Taiwan, possibly its foraging ground, for almost two months until the satellite signal went off (Fig 5).









In several studies of hospitalized sea turtles (Camacho et al., 2015; Keller et al., 2012), metabolic acidosis has been identified as a common acid/base disorder. In general, most of the blood analytes we recorded were similar to those reported previously for healthy sea turtles (Bolten and Bjorndal, 1992; Aguirre and Balazs, 2000; Hamann et al., 2006; Anderson et al., 2011; Lewbart et al., 2014; Phillips et al., 2015) .This indicated that the turtle in this study was not affected by metabolic and respiratory derangements. Green turtle is the most common species recorded in Taiwanese waters (Kuo et al., 2017; Cheng et al., 2019). Major threats to C. mydas populations worldwide include habitat degradation (Cheng et al., 2009), marine pollution (Ng et al., 2018b), disease (Chen et al., 2012; Li et al., 2017; Tsai et al., 2019), fishing activities (Chen et al., 2012) and ingestion of plastics and other anthropogenic debris (Ng et al., 2016; Jerdy et al., 2017; Jung et al., 2018; Duncan et al., 2019). Marine debris is a serious pollution problem affecting the oceans worldwide. With its increasing presence at sea, marine debris interaction pose a major threat to marine fauna (Laist, 1997). Ingestion of anthropogenic debris is well documented in sea turtles (Clukey et al., 2017; Jerdy et al., 2017; Godoy et al., 2018; Jung et al., 2018). In a dietary study of green turtles in Hong Kong by Ng et al., (2016), apart from the regular food items such as red algae, plastic fragments and a small plastic bag of tissue packaging and other foreign materials, such as rope strands, were found in the stomach contents of 2 of the 8 individuals sampled during necropsy. Marine pollution and debris has been considered one of the threats to foraging green turtles in the South China Region as revealed by Ng et al., (2016, 2018b). However, there are limited studies involving detailed analysis of anthropogenic debris obtained from fecal samples of live sea turtles.
 

Endangered green turtles are well-known to be the marine turtle species that most commonly ingest and interact with anthropogenic marine debris (Schuyler et al., 2014). Despite the recent increasing public awareness in marine pollution in Taiwan, such as banned use of plastic bags by law and beach clean-up activities organized by local concern groups, international, regional and local efforts are still required to tackle the trans-boundary pollution problem for the conservation of migratory green turtles in the vast ocean. This study presents an apparent successful rehabilitation of an endangered green turtle in Taiwan that hopefully helps further enhance public awareness and concerted actions against marine pollution in general and anthropogenic debris related problems in particular.

Rescue and rehabilitation work for sea turtles at the National Museum of Marine Biology and Aquarium (NMMBA) was approved and supported by the Forestry Bureau of Taiwan. We also thank the Southern Coastal Patrol Office for their contribution to the rescue of sea turtle and temporarily holding of the injured sea turtle.