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Fish junk food.

It is estimated that globally, 300 million tons of plastic are produced each year, and a significant amount of this ends up in the world's oceans. A study published last year estimated that about 8 million tonnes of plastic waste enter the oceans annually. In recent times, scientists have shown real concern over the growing mass of discarded plastic floating around in the oceans, killing all manner of marine creatures from whales to fry of certain species. Moves are afoot by some engineers to develop semi-automated floating machines to roam the oceans and gobble up waste plastic and other litter.

What is not widely known, is that through wave action and chemical degradation, once exposed to UV light, plastics break down into what are known as micro-plastics--fragments 5mm and less in size. These, along with micro-beads (tiny manufactured plastic beads found in cosmetic and personal care products), pose a real threat to some fish species, whose wont it is to actively seek out plastic and eat it. Scientists have been worried that these tiny fragments can build up in the guts of marine creatures and can also leach toxic chemicals.

According to a report published by the BBC, some Swedish scientific studies show that young fish become hooked on eating plastic in the seas in the same way that humans enjoy unhealthy fast food. The study found exposure to high concentrations of polystyrene makes perch larvae favour the particles over more natural foods, and this apparently leads to fry that are smaller, slower and more susceptible to predators. The researchers exposed perch larvae to different concentrations of polystyrene in test tanks. In the absence of micro-plastics, about 96% of the eggs successfully hatched; this dropped to 81% for those exposed to large quantities of micro-plastics. The fish that did hatch in waters with a high quantity of micro-plastics were "smaller, slower, and more stupid" than those that hatched in clean waters, according to lead author Dr Oona Lonnstedt, from Uppsala University. Furthermore, when predators were introduced, about half the young perch from clean waters survived for 24 hours, while those that had been raised with the strongest plastic concentrations were all consumed by pike over the same period.

What the researchers found, was that this plastic diet changed food preferences, stating, "They all had access to zooplankton and yet they decided to just eat plastic in that treatment. It seems to be a chemical or physical cue that the plastic has, that triggers a feeding response in fish", said Dr Lonnstedt. "They are basically fooled into thinking it's a high-energy resource that they need to eat a lot of". The BBC reports, "In the study, the researchers link the decline of species such as perch and pike, observed in the Baltic Sea over the past two decades, to increased deaths at the juvenile stage. They argue that if plastics are impacting young fish across species, it could have 'profound effects' on ecosystems".

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While the use of micro-beads in cosmetics has been banned in the USA, and a similar action may follow in the UK, the bigger problem of waste plastic littering the oceans is likely to be with us for decades to come.

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Title Annotation:This 'n That
Publication:African Fisherman
Date:Aug 1, 2016
Words:535
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