2 November 2018

Scion and fish make an odd combination, but biopolymer scientist Jamie Bridson was part of a team that looked at plastic microparticle ingestion by commercial fish species across the South Pacific. 

Plastic particles smaller than 5 mm (microplastics) are found everywhere in the sea. Being small, they are easily ingested by marine organisms and can find their way up the food chain from smaller fish to larger fish (and maybe to humans).

One out of four fish caught in Samoa, Tahiti, New Zealand (Auckland) and Rapa Nui (Easter Island) waters between September 2015 and October 2016 was found to have plastic microparticles in its gut. 

The New Zealand species in the trial included grey mullet, tarakihi, yellowtail kingfish, Australasian snapper and gurnard.

The gut contents of fish were dissolved then filtered to recover any plastic microparticles. The microparticles were counted and described using a microscope then the different plastic types were identified by their infrared spectra.

The researchers found 33 out of the 34 species, and about one quarter of all the fish in the study, had ingested microparticles, containing on average two pieces of plastic per individual fish. One fish from Rapa Nui was found to contain 104 pieces, which is thought to be a world record.

Overall, fish from Rapa Nui contained significantly higher levels of ingested microparticles than fish from the other three locations. The average ingestion by fish in the Auckland sample was the lowest but not significantly different to the average values of the Samoan and Tahitian samples.

The high levels of plastic microparticles found in fish from Rapa Nui is thought to be due to the island sitting in the middle of the South Pacific garbage patch – a zone of the subtropical ocean where plastic debris accumulates and the availability of food is low.

The plastics recovered were fragment, films and fibres of polyester (28%), polyethylene (26%), rayon (17%), polypropylene (9%), and others.

The research team also observed evidence of microparticles transferred from prey to predator. While this study focused on microparticle ingestion and gut contents, other workers have found microplastics in fish livers and muscle tissues. 

The results of this study emphasise how important it is to stop plastic litter reaching waterways and to develop more effective legislation and waste management systems to reduce, recycle and recover plastics.

The work was part of lead author Ana Markic’s PhD research. It was supported by the Secretariat of the Pacific Regional Environment Programme. 

Markic, A., Niemand, C., Bridson, J. H., Mazouni-Gaertner, N., Gaertner, J. C., Eriksen, M., & Bowen, M. (2018). Double trouble in the South Pacific subtropical gyre: Increased plastic ingestion by fish in the oceanic accumulation zone. Marine Pollution Bulletin, 136, 547-564.