Quarter of fish in Hauraki Gulf have microplastics in their guts, study finds

Thursday, 18 March 2021

Microplastics were found in 70 of 305 fish specimens in Auckland's Hauraki Gulf. (File photo)

A quarter of the fish from Auckland’s Hauraki Gulf sampled as part of a new study had microplastics in their guts.

The discovery comes after experiments were carried out by two masters students from the Joint Graduate School in Coastal and Marine Science.

Microplastics are pieces of plastic less than five millimetres long. They are either manufactured to be small or derived from larger plastics which have broken down into smaller pieces.

The study by Devina Shetty and Veronica Rotman has been labelled as one of the first into how microplastics are affecting New Zealand’s fish species.

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Veronica Rotman feeding fish in Niwa's Bream Bay laboratory as part of her work into whether fish are absorbing microplastics.

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Shetty focused on six fish species commonly found in the Hauraki Gulf – snapper, yellowbelly flounder, gurnard, jack mackerel, kahawai and pilchard.

Devina Shetty examing fish for microplastic injestion.

Microplastics were found in 70 of the 305 fish specimens, which included more than half of the yellowbelly flounder sampled.

“This higher ingestion rate for flounder could be due to microplastics accumulating in marine sediments which makes up more of their diet compared to other species, or it could be because the flounder samples were all obtained from the Waitematā Harbour, which is closer to Auckland as a potential microplastic source,” Shetty said.

University of Auckland research has previously found 33 out of 34 commercial fish species had evidently ingested plastic in the South Pacific, including Auckland.

Rotman, meanwhile, focused on hoki from the West Coast of the South Island, Cook Strait and the Chatham Rise.

One or more microplastics were found in the stomachs of 95 per cent of the 60 fish examined, with 90 per cent of the particles identified as fibres.

As part of a 10-week tank experiment at Niwa’s Northland Marine Research Centre, snapper were fed a diet containing polystyrene microplastic feed at different concentrations.

This led Rotman to find those fed a higher concentration were more likely to have microplastic in their white muscle tissue.

She also observed significant inflammatory, vascular and structural changes to the intestine with only a low “environmentally relevant” microplastic treatment, suggesting that similar damage is occurring in the wild.

The damage to the intestine increased with microplastic concentration, with 60 per cent of high treatment fish displaying severe alterations.

While this gut damage did not lead to any significant effects on growth or mortality in the 10-week experiment, it demonstrates microplastic has significant negative effects on the fish which eat it, Rotman said.

Dr Olga Pantos, a senior scientist in ESR’s health and environment group, said experts did not yet understand the potential human health effects of microplastics.

“There is a lot of work being carried out in this area but this area of research is still relatively new.”

She said many factors influenced the impacts of plastics in food species, including whether it was found in the guts or the flesh.

With finfish, for example, it is uncommon for the guts to be eaten, Pantos said.

“The morphology (whether fibres, beads, fragments etc), polymer type (and associated chemicals), and size may also play a role in their potential effects, and also how cooking can alter things.”

This meant there were a lot of different combinations of factors to take into account when determining the risk to human health.

“We must also be mindful of the fact that human exposure through ingestion also includes the microplastics that are in our air and settle on our plate whilst we are eating,” Pantos said.

Niwa fisheries scientist Dr Darren Parsons oversaw the projects.

He said there had only been one previous study looking at the effects of microplastics on New Zealand fish species and Shetty and Rotman’s studies provided some valuable insight into what has become an issue of huge concern.

“Microplastics are found throughout the world’s oceans, even in Antarctica. They pose a unique threat to marine life.”