by Nick Perni, RJD Intern
For decades there has been a steady increase in the production of plastic materials. Due to negligent disposal techniques and the resiliency of the material, plastic accounts for 80% of all Marine debris in some areas. The large abundance of plastic in the world’s oceans and coastal areas has detrimental effects on marine organisms. Sea turtles in particular have been heavily affected; all six species have been recorded to ingest debris nearly 90% of which is made up of plastic. The two main ways that plastic debris affects turtles is by entanglement and ingestion. Entanglement can kill organisms by preventing it from escaping predators or drowning the animal. Ingestion can also be lethal; many animals that ingest plastics can suffer from a punctured or impacted digestive system and are also susceptible to chemicals leeching from the plastic.
Qamar Schuyler and his team investigated both causes and effects of marine turtles ingesting plastic over a span of five years (2006-2011). The experiment focused on two species in particular; the Green turtle and the Hawksbill turtle. All turtles used in this experiment were already deceased and were collected for necropsies from two sources: stranded turtles from North Stradbroke Island in Queensland, Australia, and turtles from the rehabilitation facility at Underwater World, in Mooloolaba that did not survive treatment. In total 115 turtles were obtained for the study. Beach surveys on N. Stradbroke Island and on the Sunshine Coast, where the Underwater World turtles were stranded, were used to determine the amount and type of debris that the turtles encountered.
Green and Hawksbill turtles have almost identical life stages beginning their developmental stages in the open ocean (Pelagic) and returning to the coastal (Neritic) environment as latter stage juveniles to live the remainder of their lives. The different environment of these two life stages seems to be the reason for differences in probability of ingestion and debris selectivity.
Of all 115 turtles examined, 22 were in the pelagic stage and 93 were in the neritic stage. Each turtle was recorded to contain anywhere from 1-329 pieces of debris. From Schuyler’s findings he concludes that it is much more likely for smaller pelagic turtles to ingest debris than it is for larger neritic turtles. Of the 22 oceanic turtles, 12 (54.5%) had ingested debris while of the 93 coastal turtles examined, 27 (29%) were found to have ingested debris. This difference is due to the fact that most of the debris collected from the turtles digestive systems is positively buoyant, floating on or close to the surface where the oceanic turtles feed. As far as debris selectivity in the turtles examined, it was found that larger coastal-sized turtles preferred clear, soft plastic while the smaller oceanic turtles were more selective towards rubber. Of all the rubber ingested 78% were balloon fragments. When balloons are released into the air they rise to a height of about 8 kilometers then rupture into thin strands.
Since turtles are primarily visual feeders, it is obvious why these materials are the most frequently ingested items when you look at the similarities between these objects and one of the turtle’s natural preys, the jellyfish.
Other than the differing probability of ingestion between the two life stages, there were no significant differences in ingestion found between species, number of pieces, total weight of debris, and volume of debris ingested. Schuyler believes it is critical to implement pollution prevention plans, in order to stop acts such as mass balloon releases, and create appropriate waste disposal techniques worldwide. This would be an ideal start to lowering the amount of debris in our oceans and the encounters between debris and marine wildlife.
Schuyler Q, Hardesty BD, Wilcox C, Townsend K (2012) To Eat or Not to Eat? Debris Selectivity by Marine Turtles. PLoS ONE 7(7): e40884. doi:10.1371/journal.pone.0040884