Juvenile Sea Turtles and Plastic Ingestion – A Possible Evolutionary Trap? Expert Q&A
You may have seen recent news stories about the “evolutionary trap” that sea turtle hatchlings are facing with regards to plastic ingestion, sparked by the publication “Plastic Pollution and Small Juvenile Marine Turtles: A Potential Evolutionary Trap.” We caught up with Drs. Emily Duncan and Col Limpus, two of the authors of the publication, to ask them about their research, the findings, and the implications they may have for sea turtle conservation.
© Emily Duncan
SWOT: Can you explain the concept of an evolutionary trap and how it relates to sea turtle hatchlings and plastics?
Duncan & Limpus: Organisms, including sea turtles, rely on environmental cues that have developed over evolutionary time scales to make life history decisions like food choices and migrations. Because human disturbances to the environment have been rapid, formerly reliable environmental cues used by turtles may no longer be associated with favorable outcomes. As such, turtles have become “trapped” by their evolutionary responses. This is a particularly acute concern for marine turtles because they do not have the behavioral plasticity to assess and rapidly respond to evolutionarily novel situations.
Ocean plastic pollution is now widespread in the ocean environment and can mimic traditional evolutionary cues (e.g. those associated with food choices). Post-hatchling turtles now occupy pelagic waters that were once an ideal location for a reliable supply of suitable food resources to support growth and guarantee high survivorship. However, these sites now have high concentrations of plastic debris that turtles may ingest or become entangled in. This will certainly lower survivorship, and may potentially cause sub-lethal negative impacts on growth and maturity.
SWOT: How do you think hatchlings ingesting plastics could affect sea turtles at the population level?
Duncan & Limpus: Unlike other threats to sea turtles which can impact localized segments of the population, all seven sea turtle species globally are exposed to threats from floating marine debris in many stages of their lives. Hatchling turtles globally share the behavior of rapidly swimming for a few days (called the ‘swimming frenzy’) that takes them offshore into pelagic waters where, as post-hatchlings, they change their behavior to drifting with the currents and foraging on macroplankton. The pelagic habitats occupied by post-hatchling turtles now coincide precisely with areas where marine debris, especially plastics, have accumulated. The regularly-reported high occurrence of ingested plastic in post-hatchling turtles is of great concern, as related mortality and implications for eventual recruitment into breeding populations are still unquantified. Plastic ingestion is known to have negative impacts on turtles’ nutrient acquisition, pathology, and potentially on morbidity or mortality, and could possibly cause population level impacts as well, hence further study is needed to elucidate impacts on growth and survivorship.
SWOT: Did you find anything surprising or unexpected in this study? Anything that stood out that should be highlighted?
Duncan & Limpus: The study demonstrates a high incidence of plastic ingestion in small juvenile marine turtles in the Pacific and Indian Ocean, as has been reported in several other locations and populations globally, and we made significant additions to the knowledge of plastic ingestion for the flatback turtle. Despite lacking an oceanic development phase like most turtles, this species still displayed plastic ingestion. Therefore bioavailable-sized plastic must also be present in surface (pelagic) waters over the continental shelf where flatbacks feed. The presence of ingested buoyant plastics reinforces our knowledge that flatback turtles forage at or near the surface in continental shelf waters, like other sea turtle species.
SWOT: Based on the findings, what do you suggest as the next steps in terms of management and/or research?
Duncan & Limpus: We believe that these data point to the need for a major global reduction in the use of hard plastics that dominate the debris ingested by our post-hatchling turtles, as well as soft plastics such as single-use plastic bags and drinking straws.
Future research should focus on increasing knowledge of population-level mortality rates due to plastic ingestion, especially work with veterinarians, veterinary pathologists, and other specialists with access to diagnostic testing to determine plastic ingestion impacts on morbidity and mortality.
Tagging efforts with post-hatchling turtles will also be needed to quantify the spatial distributions of different rookeries and to define population trends and survivorship metrics.
Use of X-ray and ultrasound may also help to identify the presence of ingested plastics in live captured post-hatching turtles.
Learn More
Past SWOT Articles on Plastic Pollution:
Cohen, R. 2008. "There's a Great Future in Plastics…". In SWOT Report—The State of the World’s Sea Turtles, vol. 3: 28-29.
Gunn, R., & Veenstra, T. 2009. Ghostnets. In SWOT Report—The State of the World’s Sea Turtles, vol. 4: 31-33.
Savage, A., Lamilla, I., & Guillen, R. 2010. Totebags from Trash Help Turtles and Tamarins. In SWOT Report—The State of the World’s Sea Turtles, vol. 5: 40-41.
Duncan, E. 2016. Turtles and Plastic - A Case for More Action. In SWOT Report—The State of the World’s Sea Turtles, vol. 11: 6-7.
González-Paredes, D., & Estrades, A. 2018. Addressing the Plastic Pollution Challenge in Uruguay. In SWOT Report—The State of the World’s Sea Turtles, vol. 13: 42-43.
Miaud, C., & Darmon, G. 2020. Turtles Help Tackle Ocean Plastic Pollution in Europe. In SWOT Report—The State of the World’s Sea Turtles, vol. 15: 36-37.