Plastic: One Green Turtle Can Hold the Equivalent of 10 Ping-Pong Balls

[Un article de The Conversation écrit par Xia (Alice) Zhu – Chercheur postdoctoral Banting, Sciences océaniques, Université Memorial de Terre-Neuve – Chelsea Rochman – Professeur adjoint d”écologie et de biologie évolutive, Université de Toronto – et Matthew Mazloff – Chercheur, Institut océanographique Scripps, Université de Californie, San Diego]

Thousands – or even millions – tons of plastic enter the oceans each year, but their destination is poorly known. What is their final destination? How are it distributed in the ocean? This is a question still misunderstood.

For years, researchers have been trying to assemble the pieces of the puzzle. For this, they estimate the amount of plastic that the ocean can house on the surface, or in the water column and in the depths of the ocean. But in these calculations, marine animals are too often overlooked.

All animals can be plastic pollution tanks. But to illustrate how easily the oceanic plastic pollution can be stored by marine fauna, we have taken sea turtles as a case study.

Sea turtles ingest plastic debris of various shapes and sizes. For example, plastic pellets, foam, plastic bags, plastic tarpaulins, fishing equipment and food packaging. Their ingestion can have a whole series of negative effects, such as leading animals to die of inanitition, to email or even cause lesions of the intestinal mucosa. Sea turtles can also get into plastic nets and strings.

%iframe_0%

A vulnerable species

We were interested in sea turtles because we know that they are affected by plastics and that they are particularly vulnerable to the global changes that affect the ocean. Six of the seven species of sea turtles are classified as vulnerable, in danger or critical danger of extinction by the International Union for Nature Conservation (IUCN).

To estimate the quantity of plastic that remains in sea turtles, we have built a model that is based on the data available on plastic ingestion by sea turtles as well as on several additional factors that we suspect of predict the amount of plastic ingested by a turtle. These are geographic, socio-economic and ecological factors.

We estimated the size of this global tank for green turtles (Chelonia Mydas) females, because it is for this group that we had the maximum data.

We believe that at any time, we can find about six tonnes of plastic waste in the population of female green turtles. This is approximately equivalent to the amount of plastic waste contained in a garbage truck.

Based on these results, we have evaluated that only one green turtle could contain up to 26.4 grams of plastic on average, the equivalent of the mass of 10 ping-pong balls.

How to predict plastic ingestion

The place of life of turtles is also important. We have found that the sea turtles that eat near the equator are more likely than the others to accumulate plastic waste. In addition, turtles that eat near countries with lower socio-economic status are likely to eat more plastic, socio-economic status being linked to waste management.

We also found that characteristics specific to each kind of turtle, including body size and food search strategy (where and how a turtle identifies and recovers food) could also play a role.

For example, caouanne turtles) are carnivores and feed on the high seas during the first seven to fifteen years of their lives, before migrating to coastal areas close to the shore.

On the other hand, lute turtles spend most of their life on the high seas and feed on soft bodies, especially jellyfish and salps). It is therefore easy for them to confuse plastics with food.

The green turtles, on the other hand, feed mainly on seaweed and sea herbs and only spend three to five years on the high seas before moving to shallow coastal areas where they remain until the end of their lives.

These differences in behavior and size between the different species of sea turtles influence the way they are exposed to plastic debris and the amount of plastic that can enter their stomach.

It is important to understand the factors that predict plastic ingestion to determine what are the most threatened species. We have thus found that lute turtles have the greatest propensity to ingest plastic debris.

Future prospects

Sea turtles are undergoing the full whip of the problems that affect the oceans, and our plastic waste is part of the problem. The relatively constant quantity of plastic found in sea turtles raises questions about the associated risks.

As part of our study, the next step is to try to understand

If the quantity of stored plastic differs depending on animal species. What is the total quantity stored in marine animals around the world at some point?

There is an additional question: could sea turtles and marine animals in general could transport plastic waste during their trips, thus acting as plastic “treadmills” in the ocean?

A call to action

To answer these questions, we need more data on sea turtles and other species. We call for increased monitoring of sea turtles in order to improve modeling and improve the quality of information about the associated risks. We also call for further surveillance of other species and recommend normalizing the way data is recorded, as well as improving their transparency.

We hope that our results demonstrate the value of surveillance to fill the gaps in our knowledge of the plastic cycle in the environment. This knowledge could in turn contribute to the development of the world treaty on plastic pollution.

We also hope that this work will be able to provide a basis for direct actions to better protect sea turtles from plastic effects and reduce the amount of plastic that enters the ocean.