A study of mesopelagic fish found that 73 % of them had plastic in their gut!

We hear a lot about how much plastic there is in our oceans, with the craziest examples being the Great Pacific garbage patch that have often been known as “plastic islands”. It is not quite an island, but there is still a very high density of plastic particles in this area, which goes to show that the plastic we throw in the ocean ends up causing havoc on ecosystems somewhere.

A lot of plastic wash up on the beaches, but even more get eaten by fish, or just travels with the currents in the ocean. Image is Public Domain.

Today I want to talk a bit about a new study that looked at the plastic content of mesopelagic fish. A mesopelagic fish simply means that it is a fish that feeds in the mesopelagic zone, which is roughly 200 to 1,000 meters below the ocean surface.

We don't really know a whole lot about many of the species that live in this zone, but what we do know is that they are all adapted to a pretty unchanging environment with little light.

Why mesopelagic fish

Mesopelagic fish are interesting to look at for a couple of reasons. Firstly they are abundant, so there are many different species as well as many species with large populations. Secondly they are important for the transport of carbon and nutrients from the upper part of the ocean to the deep sea. Because of this we also assume that they are responsible for a lot of transportation of plastic from the ocean top to the deep sea.

This happens because the mesopelagic fish often travels up high during the day to feed on fish, and can eat fish that are not really able to travel further down into the ocean depths. The mesopelagic fish on the other hand tends to have a big vertical movement, and some species even dive really deep during the night to hide. So by doing this they have a vertical transportation of nutrients, and most likely also plastic.

Finding plastic in 3/4th of all mesopelagic fish

The research team consisted of scientists from National University of Ireland Galway, and they caught a total of 233 fish in the Northwest Atlantic, about 1,200 kilometers west from Newfoundland. All fish were caught from the depths of 300-600 meters, and consisted of fish from 7 different species.

The results show that almost three quarters of the fish the examined has plastic in their gut! Out of some of the samples species, such as Gonostoma denudatum that had plastic in every single sampled fish.

They also found that stomach fullness, and the depth at which fish were caught at did not affect the amount of plastic in their stomach, and the plastic found was similar to the plastic found at surface levels.

Read more: Plastic waste in the ocean has been found to have a twentyfold increase of disease in corals; adding one more threat to the list of things that could potentially kill corals.

How does the plastic end up in the ocean?

The big questions when we are talking about plastic in the oceans is how it ends up there, and the short answer is that it is carried by rivers to the ocean. Pretty much all plastic that is not recycled ends up in the ocean at one point. Just imagine throwing a piece of plastic into a garbage can that is already pretty full; the plastic might fall out. After this point it will eventually get carried away by the wind, and might end up in a river which carries it downstream. At one point it will most likely reach the ocean, so a lot of plastic that is thrown away in cities and in garbage bins end up in the ocean after a while.

A study has even found out that over 95 % of the plastic in the ocean originates from only 10 rivers! These are all big rivers that flows through countries with poor inhabitants, where they generally focus less on recycling. 8 of the rivers are in Asia, with the two remaining ones in Africa.

River Niger, one of the ten rivers that are responsible for 95 % of the ocean plastic pollution. Image by Guaka, posted with the Creative Commons Attribution-Share Alike 3.0 Unported license.

Some of the most common types of plastic that cause havoc in the ocean ecosystems are things such as grocery bags, plastic bottles used for soda, and plastic packaging used for food items and snacks. These are of course too large to be eaten by most fish, but they get gradually worn down by solar radiation and mechanical stress as they are carried along the currents in the ocean. Once they reach a small size they will be eaten by the fish, and get stuck in their stomach.

The plastic have long-term effect on the ecosystem

One might expect that the bad cycle of plastic ends when the fish has died from the plastic content in its gut, but the truth is that the cycle continues, and the plastic affect the entire marine ecosystem. If the fish dies a natural death it will sink to the ocean floor where the plastic will either be gradually turned to sediment, or be eaten by new species down in the depths.

Other problems arise when sea birds eat a lot of fish that has plastic in their gut, and just take a look at the image below of an albatross with its entire stomach filled with plastic!

Not much room for food here! Image by Chris Jordan, posted as Public Domain.

Getting a stomach filled with plastic is a big problem for piscivores (animals that primarily eat fish), such as many species of whales and sea birds. There have been many documented cases of both these groups of animals actually dying because of a too high plastic content in their stomach, leaving no room for real, digestible food.

We need to recycle plastic

If we want to stop this, the only solution is to recycle the plastic we use! Obviously it would be a lot better if companies started to use other types of packaging for their products, but it is generally more expensive and less durable, so that’s why they go for the easy choice and make plastic packaging.

Anyone, every single one of us is responsible for plastic pollution, even those of us who try our best to not do this. It's very easy to pollute with plastic even without meaning to, and just think about how many animals that can be saved if we all work together to reduce our usage of plastic, and become better at recycling it!

Thanks for reading

Thanks for reading about the plastic found in mesopelagic fish. I guess it’s not really a surprising study, but it goes a long way to show that even fish that live at several hundred meters depths get affected by our pollution.

PS. Sorry that I have not answered most comments and replies in the last few days; I’ve been a bit more busy than expected. But don’t worry, I’ll get back to it soon, and everyone will get their upvotes and replies :)

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