Plastic and marine turtles: a review and call for research

Sarah E Nelms,Annette C Broderick,Matthew H Godfrey,Emily M Duncan,Mark Hamann,Brendan J Godley,Tamara S Galloway,Penelope K Lindeque

doi:10.1093/icesjms/fsv165

Abstract

Plastic debris is now ubiquitous in the marine environment affecting a wide range of taxa, from microscopic zooplankton to large vertebrates. Its persistence and dispersal throughout marine ecosystems has meant that sensitivity toward the scale of threat is growing, particularly for species of conservation concern, such as marine turtles. Their use of a variety of habitats, migratory behaviour, and complex life histories leave them subject to a host of anthropogenic stressors, including exposure to marine plastic pollution. Here, we review the evidence for the effects of plastic debris on turtles and their habitats, highlight knowledge gaps, and make recommendations for future research. We found that, of the seven species, all are known to ingest or become entangled in marine debris. Ingestion can cause intestinal blockage and internal injury, dietary dilution, malnutrition, and increased buoyancy which in turn can result in poor health, reduced growth rates and reproductive output, or death. Entanglement in plastic debris (including ghost fishing gear) is known to cause lacerations, increased drag—which reduces the ability to forage effectively or escape threats—and may lead to drowning or death by starvation. In addition, plastic pollution may impact key turtle habitats. In particular, its presence on nesting beaches may alter nest properties by affecting temperature and sediment permeability. This could influence hatchling sex ratios and reproductive success, resulting in population level implications. Additionally, beach litter may entangle nesting females or emerging hatchlings. Lastly, as an omnipresent and widespread pollutant, plastic debris may cause wider ecosystem effects which result in loss of productivity and implications for trophic interactions. By compiling and presenting this evidence, we demonstrate that urgent action is required to better understand this issue and its effects on marine turtles, so that appropriate and effective mitigation policies can be developed.

Highlights

Between 1950 and 2015, the total annual global production of plastics grew from 1.5 million t to 299 million t (PlasticsEurope, 2015)
Use standardized methods to catalogue debris for comparable results Create risk maps by assessing exposure to and consequences of ingestion, i.e., utilizing satellite tracking, oceanographic and niche modelling in combination with empirical data, i.e., from necropsies for ground-truthing Understand distribution of plastic by size and type in the water column and benthic habitats and develop three-dimensional oceanographic models to understand transport and sink areas for microplastics In situ investigation of plastic passage time and breakdown in turtle gut Health studies focusing on short- and long-term impacts of plastic debris ingestion Investigate role as secondary consumers including dietary analysis using molecular and isotope techniques
Mesocosm experiments in a controlled laboratory setting Further investigation of potential for plastic consumption to lead to secondary contamination and methods to detect exposure Develop methods for the quantification of microplastics in turtle gut content Develop risk frameworks for species and populations, including detection of vulnerable life stages Develop a global online database that records incidents of exposure according to entanglement, debris type, species, and life stage Increase reports and understanding of entanglement in plastic debris from land-based sources Creating risk maps utilizing satellite tracking, oceanographic and niche modelling, and data from fisheries layers such as vessel monitoring system (VMS)

Summary

Introduction

Between 1950 and 2015, the total annual global production of plastics grew from 1.5 million t to 299 million t (PlasticsEurope, 2015). Plastics could present a major threat through ingestion, entanglement, the degradation of key habitats, and wider ecosystem effects (Barnes et al, 2009; Vegter et al, 2014; Gall and Thompson, 2015) Among these species are the marine turtles, whose complex life histories and highly mobile behaviour can make them vulnerable to the impacts of plastic pollution (Arthur et al, 2008; Ivar do Sul et al, 2011; Schuyler et al, 2014).

Land-based

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Conclusion