The conversation23 Feb 2021 18:35:14 IST
Billions of barely visible pieces of plastic float in the world’s oceans, from surface waters to deep seas. These particles, called microplastics, are typically formed when larger plastic objects such as shopping bags and food containers break down. Researchers are concerned about microplastics because they are tiny, widely distributed, and easy for wildlife to consume, accidentally or intentionally. We study maritime science and animal behavior and wanted to understand the magnitude of this problem. In a recently published study we conducted with an environmentalist Elliott Hazen, we looked at how marine fish – including species eaten by humans – ingest synthetic particles of all sizes.
In the broadest review on this topic that has been carried out to date, we found that, so far, 386 species of marine fish known to have ingested plastic debris, including 210 commercially important species. But discoveries of plastic consuming fish are on the rise. We believe this could be happening both because methods of detecting microplastics are improving and because plastic pollution in the oceans continues to increase.
Solve the plastics puzzle
It’s not news that wild creatures ingest plastic. The first scientific observation of this problem came stomach of a seabird in 1969. Three years later, scientists reported that the fish off the coast of southern New England were consuming tiny plastic particles.
Since then, more than 100 scientific papers have described the ingestion of plastic in many species of fish. But each study only provided a small piece of a very important puzzle. To see the problem more clearly, we had to put these things together.
We did this by creating the largest database in existence on the ingestion of plastic by marine fish, drawing on every scientific study of the issue published from 1972 to 2019. We gathered a range of information from each study. , including the fish species examined, the number of fish that had eaten plastic and when those fish were caught. Because some areas of the ocean have more plastic pollution than others, we also looked at where the fish were found.
For each species in our database, we identified its diet, habitat, and feeding behaviors – for example, whether it was feeding on other fish or grazing on algae. By analyzing this data as a whole, we wanted to understand not only how many fish were eating plastic, but also what factors might cause them to do so. The trends we found were surprising and disturbing.
A global problem
Our research has revealed that marine fish ingest plastic around the world. According to the 129 scientific articles in our database, researchers have studied this problem in 555 species of fish around the world. We were alarmed to find that more than two-thirds of these species had ingested plastic.
One important caveat is that not all of these studies looked for microplastics. This is probably because the discovery of microplastics requires specialized equipment, such as microscopes, or the use of more complex techniques. But when the researchers looked for microplastics, they found five times more plastic per fish than when they only looked for larger pieces. Studies that were able to detect this previously invisible threat found that plastic ingestion was higher than we initially expected.
Our review of four decades of research indicates that the consumption of plastic fish is increasing. Just from an international assessment carried out for the United Nations in 2016, the number of marine fish species found with plastic has quadrupled.
Likewise, in the last decade alone, the proportion of fish consuming plastic has doubled for all species. Studies published from 2010 to 2013 revealed that on average 15% of the fish sampled contained plastic; in studies published from 2017 to 2019, this share rose to 33%.
We believe there are two reasons for this trend. First, scientific techniques for detecting microplastics have improved dramatically over the past five years. Many of the previous studies we looked at may not have found microplastics because researchers couldn’t see them.
Second, fish are also likely to consume more plastic over time due to plastic pollution in the oceans. globally increasing. If this is true, we expect the situation to get worse. Several studies that have sought to quantify the plastic waste project as the amount of plastic pollution in the ocean keep increasing above the next decades.
While our findings may give the impression that ocean fish are filled with plastic all the way to the gills, the situation is more complex. In our review, almost a third of the species studied did not consume plastic. And even in studies showing ingestion of plastic, researchers haven’t found plastic in every fish. According to studies and species, about one in four fish contained plastics – a fraction that appears to grow over time. Fish that consumed plastic usually only had one or two pieces in their stomachs.
In our opinion, this indicates that the ingestion of plastic by fish may be widespread, but it does not appear to be universal. It doesn’t seem random either. On the contrary, we were able to predict which species were most likely to eat plastic based on their environment, habitat, and foraging behavior.
For example, fish like sharks, groupers, and tunas that hunt other fish or marine organisms for food were more likely to ingest plastic. Therefore, species higher in the food chain were more at risk.
WATCH: People ingest plastic in drinking water, but also through foods like shellfish, which tend to be eaten whole, so plastic from their digestive systems is also consumed https://t.co / ADCNQQAcRG pic.twitter.com/dtciVhybuY
– Reuters (@Reuters) December 16, 2020
We were not surprised that the amount of plastic consumed by fish also seems to depend on the amount of plastic in their environment. Species that live in ocean regions known to have a lot of plastic pollution, such as the Mediterranean Sea and the coasts of East Asia, have been found with more plastic in their stomachs.
Effects of a plastic diet
It’s not just a question of wildlife conservation. Researchers don’t know much about the effects of ingesting plastic on fish or humans. However, there is evidence that microplastics and even the smaller particles called nano plastics can pass from the stomach of a fish to its muscle tissue, which is the part that humans typically eat. Our results highlight the need for studies analyzing the frequency of transfer of plastics from fish to humans and their potential effects on the human body.
Our review is a step towards understanding the global problem of ocean plastic pollution. Of more than 20,000 species of marine fish, only about 2% have been tested for plastic consumption. And many parts of the ocean remain to be examined. Nonetheless, what is now clear to us is that “out of sight, out of mind” is not an effective response to ocean pollution – especially when it can end up on our plates.
Alexandra McInturf, PhD candidate in animal behavior, University of California, Davis and Matthieu Savoca, Postdoctoral fellow, Stanford University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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