• Anglers need to know that discarded plastic can adversely affect fish.
    Anglers need to know that discarded plastic can adversely affect fish.
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PLASTIC is the predominant type of man made debris found in today's rivers and oceans, with between 60 and 80 per cent of all marine debris today comprised of petroleum based plastics.

This is despite the fact that plastic pollution is only a relatively recent phenomena. Rafts of floating plastic at sea began to be reported in the scientific literature in the early 1970s but in the 40 years since, the problem has reached the far corners of the global oceans. Sure, the most obvious visible plastic pollution is inshore, such as those rafts of flotsam seen on our beaches and intertidal areas after flood events. However, recent science is showing this is only the tip of the iceberg and most of the problem is out of sight, out of mind.

The plastic problems getting most publicity in mainstream media in recent years have been the “garbage patch” rafts of floating plastic in the middle of the North Atlantic and North (and South) Pacific Oceans. These rafts form where ocean winds and currents concentrate floating plastics in certain places. Because of the remoteness of these locations, they certainly meet the criteria for “out of sight, out of mind”, but this doesn’t mean the problem should be ignored. Scientists have found that plastic debris in high densities can have far ranging impact on marine ecosystems, some of which are not at all obvious.

We all know through the mass media that a wide range of the usual “charismatic marine life” are impacted by plastic pollution through entanglement or ingestion, including marine mammals, birds and, most notably, turtles. However, the average angler is seldom besotted by blubber wearing or blubber eating marine beasts, being more interested in fish. So, what impact can plastic pollution have on fish? You may be surprised that the answer is, “plenty”.

The issue with plastics and fish is again, out of sight, out of mind. But in the case of fish, this is because of the microscopically small size of the plastic particles that cause the problem. The vast majority of plastic debris that finds its way into our waterways and the marine environment is non-biodegradable. In other words, the plastic cannot be broken down by natural microbial processes into carbon dioxide, methane, water, or inorganic compounds.

Most plastics, (including many that are claimed to be “biodegradable”) are in fact, “bioerodable”. Bioerosion (also known as “abiotic disintegration”) simply means the plastics break up into smaller pieces. Sometimes this process is accelerated by “oxidative embrittlement” (heat ageing) or “photolytic embrittlement” (UV ageing), but the upshot is that non-biodegradable plastics don’t disappear, they just break up into smaller and smaller pieces, eventually called microplastics when their size is reduced to less than 1mm. This is the crux of the reason why the plastic problem in our oceans doesn’t go away. It's mostly all still out there, even if you can’t see it with the naked eye.

So what? I hear you ask. How can small pieces of plastic hurt anything, let alone the fish anglers are most interested in?

The answer lies in the fact that most fish (sharks and rays and a few live bearing species excepted) start out life as planktonic larvae barely a few mm long. Planktonic fish need to feed on other planktonic organisms to survive and grow, but in some parts of the world's oceans today, there is more plastic than plankton. For example, in 1999, a US based marine research foundation found that in certain places in the North Pacific Central Gyre (middle of the North Pacific Ocean), floating microplastics outweighed zooplankton by a ratio of 6:1 and averaged over 300,000 pieces per square km. Barely ten years later, in 2008, they returned to the same location and found that the number of floating plastic particles per square km had more than doubled to 752,110, outnumbering natural plankton by over 10:1.

If this trend continued, the researchers speculated, it may affect the ability of larval and juvenile fish in the area to distinguish between plastic and natural food items, and indeed, around 35 per cent of the larval fish they studied in 2008 had ingested plastic pieces in their stomach. Now, obviously plastic provides no nutritional value to the fish, potentially reducing growth rates, but of concern were other potential effects on fish health during critical early developmental stages, such as exposure to organic pollutants and potentially hormone-altering compounds in the plastic itself.

Of course, the issue of microplastic pollution is not confined to the open ocean. A recent study done in the Great Lakes region of the United States found an average of 43,000 floating microplastic particles per square km across the lakes, with peaks of nearly half a million particles per square km downcurrent from a major city. A significant proportion of these particles were found to be plastic microbeads from cosmetics such as facial scrubs and cleansers, and other personal care products which survive sewage treatment.

These numbers highlight that today, microplastic has become a significant component of the plankton both near urbanised environments, and even far offshore. While microplastics might never choke a turtle or entangle a dolphin, they still may have significant unwanted and unforeseen effects when eaten by planktonic fish.

Of course, the upshot for anglers who care for fish is that they can help to curb the problem by always making sure all plastic bags and other such items remain secured in boats so they can’t blow overboard, and always take all your rubbish (and that of others) with you to dispose of properly in domestic waste. This includes chewed or used soft plastic tails, which are all too often thrown overboard by unthinking anglers.

These commonsense steps, together with selection of biodegradable lures and other fishing gear when it is available, will minimise the chances of anglers contributing to the relentless march of the plastic waste problem.

If you want to go even further for the fish, let other people know that anglers care about plastic too, and if you want to go the extra mile, lobbying your local council or government for better quality sewage treatment is a very good start (with reverse osmosis being the best choice for fish stocks for many reasons that, due to lack of space, we can’t go into here).


 

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