Incidence of plastic in seabirds from the tropical pacific, 1984–1991: Relation with distribution of species, sex, age, season, year and body weight

The incidence of plastic in seabirds was studied (number of individuals of a species containing plastic per number inspected, and number of particles per individual), in 1574 individuals representing 36 species of seabirds collected in the tropical Pacific, mostly between 110 and 150 ° W longitude, from 1984 to 1991. Incidence of plastic was lower in resident species compared to those which bred to the south or north but wintered in the region, and especially when compared to species that crossed the tropics in migration between the South and North Pacific. Seasonal and age-related patterns in incidence of plastic, number of particles, and particle type (pellets versus user-plastic) among a group of five Procellariiform species (each with >5% of the individuals containing plastic and for which samples were >20 birds) indicated that degradation for an individual particle in the gizzard required less than one year, and that little plastic was regurgitated by parents to chicks. Two patterns emerged from this data regarding body weight: (i) heavier birds (for a given species, age-class, season and year) were more likely to contain at least some plastic, from which we hypothesize that birds in better physical condition fed more often in areas where higher densities of plastic and food are found, such as fronts and convergences; and (ii) among individuals who contained plastic (grouped by species), there was a significant negative correlation between number of plastic particles and body weight. This is the first solid evidence for a negative relationship between plastic ingestion and physical condition in seabirds. The likelihood that higher quality individuals are more prone to ingestplastic has serious implications regarding health of some seabird populations.