Dr Roger Munro uses his 35 years of catch data to ask whether an alarming reduction in the catch-rate of flounders across much of the UK’s estuaries is linked to decades of plastic polluting both the freshwater and marine environments
Sperm counts in western men have more than halved over the past 50 years. This has led to an alarming drop in fertility rates in westernised countries and the rate of decline has doubled since 2000. This is a complicated issue involving many factors. During the 1970s the average sperm count per 1 millilitre was 100 million. Today, the “normal” count is only 49 million. But what on earth does this have to do with reduced flounder numbers in estuaries? I believe that a significant contributor is the advent of plastics. There are hundreds of research papers which show that declining sperm numbers are due to the increase in micro-plastics and their effect on reproductive hormones, not only in man but also in other animal species.
Plastic production has been increasing since the 1960s. This has completely changed the profile of waste production and has led to significant plastic accumulation in the environment. Micro-plastics have been confirmed as emerging pollutants in the marine environment due to their persistent presence and toxicity. Plastic is the most widespread type of marine debris found in our oceans, particularly in our estuaries.
MICRO PLASTICS
The main sources of plastic debris found in estuaries are land-based with plastic leakage into rivers and estuaries coming from urban and storm-water runoff, sewer overflows, littering, inadequate waste disposal and management, industrial activities, tyre abrasion, construction and illegal dumping. However, ocean-based plastic pollution originates primarily from the fishing industry, and nautical activities. Under the influence of solar UV radiation, wind, currents and other natural factors, plastic breaks down into small particles called micro-plastics (particles smaller than 5mm) or nano-plastics (particles smaller than 100nm). To put this into context, the diameter of a helium atom is about 0.06 nm. This small size makes them easy for marine life to ingest accidentally.
Fish that ingest plastics show signs of slowed digestion rates and liver toxicity. Estuarine biological information shows that fish found particularly near industrial areas encounter much higher plastic concentrations in water columns and sea-bed deposits than those in the open ocean. This may, in part, explain why flounder catches on our beaches don’t appear to be as badly affected as those in estuaries. Given
