Mapping marine debris encountered by albatrosses tracked over oceanic waters

Abstract

Anthropogenic marine debris is a threat to marine organisms. Understanding how this debris spatially distributes at sea and may become associated with marine wildlife are key steps to tackle this current issue. Using bird-borne GPS- and video-loggers on 13 black-footed albatrosses Phoebastria nigripes breeding in Torishima, Japan, we examined the distribution of large floating debris in the Kuroshio Current area, western North Pacific. A total of 16 floating debris, including styrofoam (n = 4), plastic pieces (n = 3), plastic sheet (n = 1), fishery-related items (rope or netting, n = 4), and unidentified debris (n = 4), were recorded across the 9003 km covered by nine birds. The debris was concentrated in the southern area of the Kuroshio Current, where the surface current was weak, and the albatrosses were foraging. The albatrosses displayed changes in flight direction towards the debris when at a mean distance of 4.9 km, similarly to when approaching prey, and one bird was observed pecking at a plastic sheet; indicating that albatrosses actively interacted with the debris. This paper shows the usefulness of studying wide-ranging marine predators through the use of combined biologging tools, and highlights areas with increased risk of debris exposure and behavioral responses to debris items.

Figure 1

Distribution of marine floating debris (red circles) encountered by black-footed albatrosses at sea in relation to their foraging area (purple lines: 95% kernel density contour of the on-water bout locations where the birds fed on squid or fish confirmed from video footage). GPS tracks of 23 foraging trips made by 13 birds from Torishima (yellow triangle) are shown by gray lines, with green sections symbolizing when concomitant video records were available. Black arrows show surface ocean current during 15 February–2 March 2017, when field survey was conducted. Isobaths of 500 m are shown by black line. Red square represents study area of Yamashita and Tanimura (2007) where small floating plastic samples were collected using a neuston net over the Kuroshio Current. The figure was generated with the ArcGIS Desktop 10.7.1 software (https://www.esri.com/en-us/home).

Figure 2

Examples of marine debris floating at the sea surface, recorded by video-loggers fitted on black-footed albatrosses breeding on Torishima, Japan. Styrofoam recorded from Bird 31 (a), styrofoam, Bird 48 (b), plastic, Bird 39 (c), plastic with barnacles, Bird 42 (d), styrofoam with barnacles, Bird 46 (e), fishing net with barnacles, Bird 49 (f), fishing net and rope with barnacles, Bird 49 (g), rope used in fisheries, harboring a Aluterus scriptus filefish, Bird 43 (h), and Bird 44 pecking at a plastic sheet (i). Images were extracted from footage taken during flight bouts (a–c), or during sitting-on-water bouts (d–i).

Figure 3

Comparison of the behavioral response of black-footed albatrosses to debris and prey. Reaction distance toward debris (n = 9) and prey (n = 46) (a). On-water bout durations between those with debris (n = 9) and prey (n = 61) (b). Results of Mann–Whitney U test are shown in each panel.