Jellyfish (Pelagia noctiluca) trapped in plastic, Kornati, Croatia.
Jellyfish (Pelagia noctiluca) trapped in plastic, Kornati, Croatia. Image: Matko Pojatina
© WWF-Adria / Matko Pojatina

This article was originally published by WWF-Australia.

There's been a great deal of coverage on the amount of plastic entering the oceans: We now know that over 100,000 marine mammals and one million seabirds die every year as a result of plastic pollution, and some parts of the ocean resemble huge vats of plastic soup.

But what about the fish?

By 2050 it's estimated that there will be more plastic than fish in the ocean (by weight), and there are concerns over how this will impact food chains. This means us.

Plastic and the Great Pacific Garbage Patch

When we think of rubbish in the ocean, the most common mental images are of the Great Pacific Garbage Patch.

The Great Pacific Garbage Patch sits between Hawaii and California and is the biggest accumulation of ocean plastic on the planet. It covers an area roughly twice the size of Texas, and contains an estimated 1.8 trillion pieces of plastic weighing nearly 80,000 tonnes.

However, while larger objects contribute most to the visual impact of the Great Pacific Garbage Patch, when it comes to object count, 94% is represented by microplastics.

These microplastics are created by sunlight and waves breaking down larger plastic objects, and it's estimated that today there are 51 trillion of these particles in the oceans.

Microplastics are what we're most interested in when it comes to fish.

70% of deep sea fish have eaten plastic
70% of deep sea fish have eaten plastic Image: WWF-Australia
© WWF-Australia

Why do fish eat plastics?

Microplastics measure less than five millimetres, and one simple reason that fish eat them is that they can look a lot like food that fish naturally hunt. However, this might not be the whole story.

A recent study involving anchovies, one of the fish species found to be eating microplastics, shows that smell may also play a part in this occurrence. You can see the fish's logic: if it smells like food and looks like food, chances are it's food.

While it's worrying enough that fish are eating plastic, anchovies were chosen partly because of their position in the marine food chains. Anchovies eat krill but in turn are eaten by creatures ranging from other fish to whales, birds and even humans.

It's already been shown that plastics will pass up the food chain from prey to predator - the presence of plastics in endangered southern bluefin tuna captured near Tasmania was attributed to their predation on smaller fish species - so are we eating plastics?

Are there microplastics in the fish we eat?

The short answer is 'Yes', and it doesn't stop with anchovies.

In fact 12 of the 25 most important species for global fisheries industries were found to have consumed microplastics, according to research published in 2017. The species named included dinner time favourites such as chub mackerel, Atlantic herring, blue whiting and sardines, as well as bivalves including oysters and mussels.

With the same study showing that Oceania is the continent with the highest per capita consumption of fish, what does all of this mean for Australians?

Starfish (Fromia monilis) stuck on a plastic calculator trashed near Banda Neira, Indonesia
Starfish (Fromia monilis) stuck on a plastic calculator trashed near Banda Neira, Indonesia Image: Jurgen Freund
© Jurgen Freund / WWF

Should we be concerned?

For birds and marine mammals, the sheer amount of plastic consumed can be enough to cause death through punctured intestines or starvation. For humans, this isn't the case. What concerns scientists isn't the volume of plastic consumed, but the associated chemicals.

Plastic products contain a large number of additives, including stiffeners like bisphenol A (BPA). While the exact effects of consuming plastic that comes from a marine environment are unknown, it's worth noting that, in high enough doses, BPA has strong links to cancer for some individuals.

Oceanic plastics also have the opportunity to pick up additional water-borne pollutants which wash into the waters as a result of human activity. These include heavy metals, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). All of these can easily adhere to the surface of debris in the ocean, and will enter into the food chain when the plastic is ingested.

The good news from our point of view is that, when microplastics have been found in fish, they have been in the gut, whereas the meat we eat comes from the muscle tissue. Even species such as mussels, anchovies and oysters, which are eaten whole, are likely to contain only negligible amounts of microplastics.

However, there's concern for the future.

As microplastics continue to break down, they eventually become nanoplastics. Invisible to the human eye, these plastics can penetrate cells, and have the frightening capability to enter tissues and organs.

For now researchers are unable to identify nanoplastics in food, so there's no data on whether they're already being absorbed by humans, or the exact effects they may have. But it's likely that in the future a clearer picture will emerge.

What we do know is that animals at all stages of the food chain are feeling the effects of plastic pollution, and the situation is only going to get worse if human behaviour doesn't change.

On an individual level you can pledge to #ReduceYourUse or participate in beach litter collections. When it comes to fighting plastic, only a unified response can lead to meaningful change.