The boat rocks lightly. A fisherman stares down at his net in the water patiently. When he pulls it up, the catch could be described as meager, at best. One would expect overfishing to be the culprit of lower fish catches these days. Or maybe climate change. But, there is one threat lurking beneath the water’s surface that could be causing some serious issues for fish and fishermen—microplastics.
A recent study conducted by Oona M. Lonnstedt and Peter Eklov at Uppsala University in Sweden shows just how much of a threat microplastics can be. Lonnstedt and Eklov studied Eurasian perch larvae, a freshwater perch native to Europe and northern Asia, which is fished for food and game.
Example of Eurasian perch larvae used in study.
The researchers found that microplastics are making fish stupider and lazier. Microplastics inhibited the fish larvae’s abilities to avoid and detect predators. They also reduced their activity levels, how many hatched from their eggs, and their body size.
Microplastics are pieces of plastic less than 5mm in length, which is a little less than the width of a wooden pencil. Plastic is not biodegradable, so over time it breaks down into smaller and smaller pieces called microplastics.
Scientists suspect these pieces of plastic will last hundreds to thousands of years or more in the environment. That potato chip bag that blew out of my hand on a whale watching boat ten years ago? It’s still in the water, but not so visible to us anymore.
Lonnstedt and Eklov’s research comes at a time when microplastics are raising international concern for their potential health effects in marine organisms and humans. In February, another study revealed that microplastics impair oyster reproduction. Other studies are finding that microplastics are showing up in much of our seafood and even sea salts. There is concern among scientists that if we ingest enough microplastics we may experience health effects similar to those shown happening in marine creatures, like infertility.
Almost half of the human population depends on fish for protein or on fishing for their livelihoods. In 2013, 3.1 billion people depended on fish as a primary source of animal protein. 12% of the world’s population depends on fisheries for their income. More than 90% of these people are small scale fishers.
According to Lonstedt and Eklov’s research, the fish populations people depend on could be in serious jeopardy if microplastic concentrations continue to increase.
For their study, Lonnstedt and Eklov reared Eurasian perch larvae in aquariums with three different microplastic concentrations: no microplastic particles, a current environmentally realistic concentration of microplastics, or a high concentration of microplastics. The larvae placed in high microplastic concentrations were less healthy and more likely to be killed by predators.
Eurasian fish larvae from study that has filled its belly with microplastics, the small clear dots.
When placed in a simulated natural environment with juvenile pike fish, a natural predator to young perch, all of the perch fish larvae that grew in high concentrations of microplastics were killed after 24 hours, compared to two-thirds of perch reared in an average microplastic concentration. Those reared in water with no microplastics did the best: only one half of the fish died.
Most surprisingly, Perch reared in the highest level of microplastics seemed to actually prefer eating plastic particles rather than their natural food. Plastic is not nutritional so, not surprisingly, these young fish were significantly smaller and weighed significantly less.
Though more research needs to be completed, this study indicates that microplastics could have wide-ranging effects on fish populations and, consequently, entire food webs if other fish larvae react similarly to microplastics.
This is bad news for fish and people. Many communities depend on fish as a means to survive and for their livelihood. If fish actually prefer eating plastic over their natural food sources, that means when we eat seafood, we will be consuming more microplastics too.
We create and throw away more plastic everyday. This study highlights the need for better management of plastic waste and the importance of further research on microplastics, an unseen, but all too real threat for fish, fisheries, and ourselves.