Humans cause a lot of problems for sea turtles, in spite of the status of these reptiles as charismatic megafauna: destruction of habitat, disturbance of nesting sites on beaches, egg theft, hunting, pollution, and accidental death and injuries through fishing and boating. Three Brazilian researchers (Bugoni et al., 2001) examined yet another anthropogenic impact, ingestion of plastic debris, on sea turtle populations, in the southern part of their country. They collected stranded sea turtles along the coast of the state of Rio Grande do Sul, measured the curved carapace length to determine age classification, and removed the foregut region (esophagus and stomach) of the digestive tract to analyze number and weight of plastic pieces ingested.
For the Green Turtles (Chelonia mydas) in the study, 23/38 had ingested anthropogenic debris, and even this high percentage may have been an underestimate. Plastics were by far the most frequent type of debris found, but one of the Green Turtles appeared to have ingested oil and tar from a recent spill at a nearby offloading terminal. Most of the plastic debris was in the form of ropes and bags, and the plastic bags were predominantly white (28.9%), transparent (39%), or black (18.4%); plastic bags are thought to be mistaken as jellyfish by the Green Turtles. Four of the 23 Green Turtles appeared to have died from gut obstruction by the plastic debris. Bugoni and colleagues also analyzed 10 Loggerhead Turtles (Caretta caretta), which had a lower frequency of ingested plastic debris than did Green Turtles, perhaps because of their wider digestive tracts or benthic foraging habits.
Green Sea Turtle, Chelonia mydas
Photo: NOAA Photo Library
A more recent study included two stranded sea turtles, one Green Turtle and one Olive Ridley Turtle (Lepidochelys olivacea), found along the northeastern coast of Brazil, Paraíba state. Mascarenhas and colleagues (2004) pointed out that both debris ingestion and entanglement in items such as lines, plastic ropes, and nets can cause serious injury and death in sea turtles. The Olive Ridley Turtle in this study was found with several large external wounds from a boat propeller, and nine pieces of hard plastic in the stomach. The Green Turtle was found alive, with a fractured maxilla and frontal bone, but subsequently died during the rehabilitation period. This animal had experienced an intestinal perforation, likely due to hard, sharp plastic pieces that it had ingested. From these two Brazilian studies, and similar ones in other parts of the world, it is clear that ingestion of plastic and tar is a significant cause of non-natural deaths in sea turtles.
Bugoni, L., Krause, L., and Petry, M.V. (2001). Marine debris and human impacts on sea turtles in Southern Brazil. Marine Pollution Bulletin 42(12), 1330-1334.
MASCARENHAS, R. (2004). Plastic debris ingestion by sea turtle in Paraï¿½ba, Brazil. Marine Pollution Bulletin, 49(4), 354-355. DOI: 10.1016/j.marpolbul.2004.05.006