Global analysis of anthropogenic debris ingestion by sea turtles

Abstract

Ingestion of marine debris can have lethal and sublethal effects on sea turtles and other wildlife. Although researchers have reported on ingestion of anthropogenic debris by marine turtles and implied incidences of debris ingestion have increased over time, there has not been a global synthesis of the phenomenon since 1985. Thus, we analyzed 37 studies published from 1985 to 2012 that report on data collected from before 1900 through 2011. Specifically, we investigated whether ingestion prevalence has changed over time, what types of debris are most commonly ingested, the geographic distribution of debris ingestion by marine turtles relative to global debris distribution, and which species and life-history stages are most likely to ingest debris. The probability of green (Chelonia mydas) and leatherback turtles (Dermochelys coriacea) ingesting debris increased significantly over time, and plastic was the most commonly ingested debris. Turtles in nearly all regions studied ingest debris, but the probability of ingestion was not related to modeled debris densities. Furthermore, smaller, oceanic-stage turtles were more likely to ingest debris than coastal foragers, whereas carnivorous species were less likely to ingest debris than herbivores or gelatinovores. Our results indicate oceanic leatherback turtles and green turtles are at the greatest risk of both lethal and sublethal effects from ingested marine debris. To reduce this risk, anthropogenic debris must be managed at a global level.

Keywords: Caretta caretta; Dermochelys coriacea; Eretmochelys imbricata; Lepidochelys kempii; basura; escombros; garbage; litter; residuos; rubbish; trash.

Figure 1

Change in probability of ingestion of debris over time for different species of sea turtles (black dots, presence [1.0] or absence [0.0] of debris in turtles from one iteration of a Monte Carlo function; gray lines, inverse logit calculation of the probability of a turtle ingesting debris on the basis of the median slope and intercept for 100 iterations of the Monte Carlo function; p values, median values for 100 iterations of the Monte Carlo function). For the leatherback turtle graph, data are for all leatherback turtles, and for the leatherback post 1985 graph, data from Mrosovsky et al. (2009) are excluded.

Figure 2

Total number of studies reporting on ingestion of particular types of marine debris by sea turtles. In many cases, multiple types of debris were found, so a study could be counted in more than one category.

Figure 3

Locations of studies of ingested debris by sea turtles worldwide (enlargements: [a] the Gulf of Mexico and [b] the Mediterranean) overlaid on a 30-year model of global debris distribution (red and yellow areas on maps, high debris concentration) (Lebreton et al. 2012). Circles are sized relative to the total number of turtles necropsied (large, 100 turtles; small, 10 turtles). Red areas in circles indicate the percentage of turtles in each study found with ingested debris. All species have been amalgamated. (Background map reprinted from Marine Pollution Bulletin [Vol. 64], L. C.-M. Lebreton, S. D. Greer, and J. C. Borrero. Numerical Modelling of Floating Debris in the World’s Oceans. Pages 653–661. Copyright 2012, with permission from Elsevier.)

Figure 4

Percentage of the total number of each species of turtle across all studies that were reported to have ingested debris. Different letters above bars indicate significant differences between species (p < 0.05) (n, total number of turtles necropsied for each species).