Threat of plastic pollution to seabirds is global, pervasive, and increasing

Abstract

Plastic pollution in the ocean is a global concern; concentrations reach 580,000 pieces per km(2) and production is increasing exponentially. Although a large number of empirical studies provide emerging evidence of impacts to wildlife, there has been little systematic assessment of risk. We performed a spatial risk analysis using predicted debris distributions and ranges for 186 seabird species to model debris exposure. We adjusted the model using published data on plastic ingestion by seabirds. Eighty of 135 (59%) species with studies reported in the literature between 1962 and 2012 had ingested plastic, and, within those studies, on average 29% of individuals had plastic in their gut. Standardizing the data for time and species, we estimate the ingestion rate would reach 90% of individuals if these studies were conducted today. Using these results from the literature, we tuned our risk model and were able to capture 71% of the variation in plastic ingestion based on a model including exposure, time, study method, and body size. We used this tuned model to predict risk across seabird species at the global scale. The highest area of expected impact occurs at the Southern Ocean boundary in the Tasman Sea between Australia and New Zealand, which contrasts with previous work identifying this area as having low anthropogenic pressures and concentrations of marine debris. We predict that plastics ingestion is increasing in seabirds, that it will reach 99% of all species by 2050, and that effective waste management can reduce this threat.

Keywords: extinction; ingestion; marine debris; risk analysis; seabird.

Fig. 1.

Plastic ingestion by seabirds as reported in the literature (1962–2012). (A) Frequency of individuals with plastic fragments in their digestive system per species–study combination. (B) Proportion of individuals in each species–study combination having plastic in their digestive system with time. Plot shows median and quartiles, with bars extending to 1.5 times the interquartile range. (C) Date of first discovery of plastic ingestion for seabird species across all species identified in the literature review.

Fig. 2.

The expected number of seabird species ingesting plastic and driving factors. Predictions are at the 1 × 1 degree scale. (A) The expected number of species ingesting plastic based on predictions from a generalized linear mixed model, using a random effect to represent taxa-specific ingestion rates (n = 186). (B) The expected number of species ingesting plastic, as in A, but based on a generalized linear model using fixed effects for taxa-specific ingestion rates (n = 92). (C) Modeled concentration of marine debris in the world’s oceans on a log scale. (D) Species richness for seabirds considered in this study, based on data from Birdlife International (32).