Ingestion and indigestion of plastic in turtles

Photo courtesy of USFWS Pacific  

Many marine turtles have been found to consume plastic debris items, often mistaking it for food items. The most common example of this is the consumption of plastic bags, which look and move like jellyfish in water, the most common (and in some cases exclusive) food item in the diet of marine turtles.

The contents from the stomach of a single juvenile turtle, found off the coast of Argentina in 2011, was found to contain over 400 pieces of plastic. Unsurprisingly, these sharp plastic shards were the cause of this animal’s death, which impacted upon and caused obstruction of the oesophagus. Unfortunately this is not an isolated event, rather an increasingly common one. Other cases have revealed a green turtle off the coast of Australia with 317 pieces of plastic in its stomach and intestines, and the monitoring of another individual off the Florida coast revealed 74 foreign man-made objects including four types of latex balloons, various hard plastics, as well as a piece of carpet-like material and two tar balls. With rising levels of non-biodegradable plastic pollution in our oceans, the chances of marine turtles and other wildlife encountering and consuming or becoming entangled in plastic debris items are ever increasing.

An estimated 260 million tonnes of plastic are produced a year, with a huge amount ending up in the world’s oceans and continually circulated by its powerful currents. One such significant convergence exists in the Pacific Ocean, known as the great pacific garbage patch. This gyre of marine litter is approximately the size of Texas and contains an estimated 3.5 million items of detritus, making it the largest mass of oceanic debris in the world.

The complex structure of most plastics means that most varieties do not biodegrade like other marine debris; instead they photodegrade, disintegrating into smaller and smaller pieces whilst still remaining a polymer. Even in this micro state, plastic is still detrimental to marine life; the plastic flotsam concentrates into the upper levels of the water column where it is ingested by the smallest marine organisms, such as plankton. From this level, plastic moves up through the food chain via the many marine creatures that consume plankton as food.

All seven species of marine turtle are listed on the IUCN (International Union for Conservation of Nature) Red List of Endangered Species as either "endangered" or "critically endangered". Even though they lay around one hundred eggs at a time, on average only one out of a thousand will survive to adulthood. Many natural occurrences already endanger marine turtles, including predation (especially of hatchlings), and currents which drag individuals from their native warmer waters into colder seas where they become cold shocked and die. However, many new threats to sea turtle species have arisen and increased due to the presence of humans. Such problems include egg collection, collisions with boats and interactions with fisheries. Pollution with plastics is perhaps the most unnecessary contribution to the decline of turtles, and one that can be significantly reduced. With numbers already low, threats to marine turtle populations are perhaps more significant than ever and any further increase may eventually see this remarkable animal disappear from our seas forever.

By Will Matthews