Too much plastic in the guts of deep sea fish, says study

New study finds much higher occurrence of microplastic fragments, mainly polyethylene fibres, in the gut contents of mesopelagic fish


Three in four deep sea fish have plastic in their stomachs, a new study revealed.

The figures are much higher than what scientists found in earlier such studies, raising an alarm on the potential secondary implications for other species and the wider ecosystem.

“Overall, we found a much higher occurrence of microplastic fragments, mainly polyethylene fibres, in the gut contents of mesopelagic fish than previously reported,” according to the study reported in the Frontiers in Marine Science journal.

Th study detected a “significantly higher occurrence rate” of 73% in contrast to previous studies reporting occurrence rates of 11% in the North Atlantic, and 9% and 35% in the North Pacific Gyre regions.

Using forensic methods, the study assessed microplastic frequency of occurrence in mesopelagic fish gut contents from a warm-core eddy in the Northwest Atlantic.

“Stomach fullness, species and the depth at which fish were caught at, were found to have no effect on the amount of microplastics found in the gut contents.

“However, these plastics were similar to those sampled from the surface water. Additionally, using forensic techniques we were able to highlight that fibres are a real con- cern rather than an artefact of airborne contamination,” according to the report in the journal run by an open-access academic publisher.

“Meso” means intermediate and mesopelagic, or midwater, “fish” refers to fish that live in the intermediate pelagic water masses between the euphoric zone at 100m depth and the deep bathypelagic zone where no light is visible at 1,000m, according to an article in the Encyclopedia of Ocean Sciences.

Most mesopelagic species make extensive vertical migrations into the epipelagic zone at night, where they prey on plankton and each other, and thereafter migrate down several hundred metres to their daytime depths, the article added.

Commenting on the findings, Stockholm-based water purification company Bluewater Group co-founder and CEO Anders Jacob- son said it was “extraordinarily worrying that plastic particles have now been found in three out of four deep sea fish thousands of kilometres from land”.

In a paper published in Science Advances last year, it was estimated that 8.3 billion metric tonnes of plastic had been produced in the 65 years since the 1950s when mass production of plastics began.

It was said that some 60% of that, or 4.9 billion tonnes, had already ended up in landfills or polluting the environment.

If the current production, use and waste management trends continue, the study projected that the total amount of plastic dumped in landfills or polluting the natural environments by 2050 will hit 12 billion tonnes.

‘Great Concern’

In the latest study on plastics and fish, the authors noted that such high numbers of microplastics in the gut contents of mesopelagic fish are of “great concern”.

It noted that microplastics have previously been shown to adversely impact invertebrate species such as lugworms, causing weight loss, reduced feeding activity and inflammation.

“The ingestion of microplastics by mesopelagic fish may also have secondary implications for other species, as well as the entire ecosystem,” the study said.

It added that mesopelagic fish are now known to make up a substantial biomass in the pelagic realm and provide an important food source for many large predators such as dolphins, seals, tuna, as well as sea birds.

The study noted that microplastics are a ubiquitous pollutant in seas today and known to have detrimental effects on a variety of organisms.

“Over the past decade, numerous studies have documented microplastic ingestion by marine species with more recent investigations focusing on the secondary impacts of microplastic ingestion on ecosystem processes,” it said.

However, it noted that few studies so far have examined microplastic ingestion by mesopelagic fish, which are one of the most abundant pelagic groups in oceans.

Through its vertical migrations, they are known to contribute significantly to the rapid transport of carbon and nutrients to the deep sea.

“Therefore, any ingestion of microplastics by mesopelagic fish may adversely affect this cycling and may aid in transport of microplastics from surface waters to the deep sea benthos,” it said.