Bringing Home the Trash: Do Colony-Based Differences in Foraging Distribution Lead to Increased Plastic Ingestion in Laysan Albatrosses?

Abstract

When searching for prey, animals should maximize energetic gain, while minimizing energy expenditure by altering their movements relative to prey availability. However, with increasing amounts of marine debris, what once may have been ‘optimal’ foraging strategies for top marine predators, are leading to sub-optimal diets comprised in large part of plastic. Indeed, the highly vagile Laysan albatross (Phoebastria immutabilis) which forages throughout the North Pacific, are well known for their tendency to ingest plastic. Here we examine whether Laysan albatrosses nesting on Kure Atoll and Oahu Island, 2,150 km apart, experience different levels of plastic ingestion. Twenty two geolocators were deployed on breeding adults for up to two years. Regurgitated boluses of undigestable material were also collected from chicks at each site to compare the amount of plastic vs. natural foods. Chicks from Kure Atoll were fed almost ten times the amount of plastic compared to chicks from Oahu despite boluses from both colonies having similar amounts of natural food. Tracking data indicated that adults from either colony did not have core overlapping distributions during the early half of the breeding period and that adults from Kure had a greater overlap with the putative range of the Western Garbage Patch corroborating our observation of higher plastic loads at this colony. At-sea distributions also varied throughout the year suggesting that Laysan albatrosses either adjusted their foraging behavior according to constraints on time away from the nest or to variation in resources. However, in the non-breeding season, distributional overlap was greater indicating that the energy required to reach the foraging grounds was less important than the total energy available. These results demonstrate how a marine predator that is not dispersal limited alters its foraging strategy throughout the reproductive cycle to maximize energetic gain and how this has led to differences in plastic ingestion.

Baseline for beached marine debris on Sand Island, Midway Atoll

“…Some of the identifiable items, as well as debris pieces, we found on the beaches of Sand Island have also been found in Laysan Albatross (Phoebastria immutabilis) chicks (Auman et al, 1997;Petit et al, 1981); these items and pieces are fed to chicks by the adults which feed in the North Pacific Gyre (Young et al, 2009). The large amount of plastic pieces on Sand Island, including pieces smaller than those collected in our study (McDermid and McMullen, 2004), is indicative of the larger issue of plastic degradation on beaches (Corcoran et al, 2009).…”

Individual-level Variation and Higher-level Interpretations of Space Use in Wide-ranging Species: An Albatross Case Study of Sampling Effects

“…Commonly in multi-colony tracking studies, the size of the areas used and the degree of at-sea spatial segregation among seabird colonies are delineated by a pooled KDE from a sample of tracked individuals from each group. The size of pooled KDE 50 or 95% contours are quantified and compared, and the degree of overlap between groups is calculated (e.g., Young et al, 2009;Frederiksen et al, 2012;Thiebot et al, 2012;McFarlane Tranquilla et al, 2013;Ratcliffe et al, 2014). However, without consideration of individual variation within an available dataset, these higher-level inferences can be inadvertently misleading.…”

“…Defining period-specific space use can help to identify the source or severity of common or distinct threats posed at different periods in the annual cycle for a species, and for further sub-groups divided by for example age-class (e.g., Péron and Grémillet, 2013;Riotte-Lambert and Weimerskirch, 2013;Gutowsky et al, 2014a), or sex (e.g., Phillips et al, 2004;Hedd et al, 2014). At the colony level, individual-based tracking data have been used to discern period-and colony-specific space use and potential associated impacts for population dynamics for a variety of seabird species (e.g., Young et al, 2009;Catry et al, 2011;Gaston et al, 2011;Wakefield et al, 2011;Frederiksen et al, 2012;McFarlane Tranquilla et al, 2013).…”

“…from the same colony during breeding), and the practice has since become commonplace. Some recent examples include the use of pooled KDE to compare space use between different annual periods for a species and colony (e.g., Robertson et al, 2014), different species from the same colony (e.g., Linnebjerg et al, 2013), different colonies of the same species (e.g., Young et al, 2009;Thiebot et al, 2011), and different species and colonies (e.g., McFarlane Tranquilla et al, 2013Tranquilla et al, , 2015Ratcliffe et al, 2014). …”

“…GLS recovery rates varied among years but were on average 77% at Midway (2008-2013) and 91% at Tern (2008. While it was not possible to formally assess tag effects, deployments at a Laysan albatross colony on Oahu, Hawaii resulted in no detectable short-term effects on reproductive success (Young et al, 2009 …”