Scientists warn of trawler damage to coastal waters

Crucial role of Britain’s shelf seas in absorbing carbon dioxide is under threat, says report, explains this article from The Observer.

The shallow seas around Britain absorb tens of million of tonnes of carbon dioxide from the atmosphere every year, scientists have discovered. This plays a critical role in stabilising the country’s ecology and in lessening the impact of carbon emissions.

But researchers warn that shelf seas are increasingly vulnerable to climate change and the impact is likely to worsen. In particular, rising temperatures and increased numbers of intense storms threaten to disrupt the coastal regions’ ability to absorb carbon dioxide. This could accelerate climate change, they state in Shelf Seas: The Engine of Productivity, published this week.

“The seas round Britain are some of the best-studied in the world,” said one author, Phil Williamson of the University of East Anglia. “Yet we are only just finding out how its many complex processes fit together.”

UK shelf seas have an average depth of 80 metres and cover 1.6m sq km, an area nearly six times Britain’s land area, and are worth £47bn to the economy. By comparison, the entire north-west European shelf sea covers 3.2m sq km, adds the report on the UK Shelf Sea programme.

Although shelf seas comprise only around 7% of the world’s oceans, they support more than 90% of global fish catches. However, they are coming under increasing stress from overfishing, pollution and trawling of the seabed as well as increased shipping, the erection of offshore wind farms and the construction of oil rigs.

UK Carbon Emissions

All these activities have impacts on the battle to limit global warming. According to the report, the north-west European shelf sea – half of which is made up by UK coastal waters – absorb 15-40m tonnes of atmospheric carbon dioxide a year, “the equivalent of between 10 to 25% of all UK carbon emissions”.

Some of this carbon is held in the water above the seabed but most – 70% to 88% – has been found in the top 10cm of sediments that make up the UK shelf seas floor. If this carbon is released the consequences could be severe.

According to the report, the potential release – from direct human action and indirectly from global warming – of the carbon dioxide in the north-west European shelf sea could result in around £9bn of damage over the next 25 years, much of it in the UK.

The report also highlights the dangers posed by trawling, the most widespread human activity in Britain’s shelf seas. Weighted nets dragged across the sea floor kill many more forms of marine life than the fish they are designed to catch.

Crucially, the researchers found that a single, initial trawl of a new seabed zone causes most damage while subsequent trawls do less. That means that full exclusion zones – in which no trawling is allowed – will have a greater benefit than allowing different levels of trawling in different zones. This “suggests there should be an all or nothing approach to marine protection zones”, said Williamson.

This article was originally published as Scientists warn of trawler damage to coastal waters at The Observer on 28/10/18.