By Ola Wietecha, undercurrentnews – November 23, 2015
An ongoing two-year independent study on trawling and its effect on benthic sea life — species that live on sea floors where trawling occurs – has found that the practice may not be as devastating as it is portrayed by some NGOs.
The study called, ‘Trawling: Finding Common Ground on the Scientific Knowledge Regarding Best Practices’, is being funded by the Walton Foundation and the Packard Foundation in partnership with the National Fisheries Institute, and is being done by a group of international scientists who are collecting and assessing data of global sea floors where trawling occurs.
The major data collection and analysis for the project has been completed, including assessments of mobile bottom contact gear in Europe, Australia, New Zealand, Argentina, South Africa and most of the US, making it six times more extensive than and previous compilations.
According to Ricardo Amoroso of the University of Washington, who presented the data at this year’s Pacific Marine Expo in Seattle, public perception of trawling is often negative. Common public beliefs include the equivalent of 10 football fields are trawled every four seconds and that trawling is turning the seafloor into a desert.
“What we want to do with this project is actually contract these perceptions with data,” he said.
A major problem, Amoroso said, is that data are often represented by low resolution square cells, each representing several hundred kilometers.
“It’s the way that local management agencies are collecting the data, but this is problematic in terms of trying to assess the footprint,” he said.
Within each one of these cells there is a wide range of fishing activity, with some areas being heavily trawled and others remaining virtually untouched.
One important aspect of this report, Amoroso said, was to represent the data using the highest resolution possible, mostly at 1 kilometer squared, in order to get a more accurate representation of how much of the seafloor was being trawled.
“When we use one square kilometer resolution our perception is that 70% of the area has never been trawled, as soon as we change the resolution to 10km, 50% of the area has been untrawled, and if we change the resolution to 40 square kilometers, only 30% has never been trawled,” he said.
The team found that trawling tends to be highly concentrated, rather than widespread and in fisheries where they have data, they have found that trawling is either declining or is stable.
“Is trawling everywhere? Nope, fishing efforts tend to be very aggregated in very specific places…is the footprint of trawling increasing globally? There are many places in the world where we don’t have data, but for the places where we do have data, we have seen that management has absolutely been able to stabilize or reduce fishing pressure,” Amoroso said, negating the list of common misperceptions he began his presentation with.
In terms of trawling on sea life, another aspect of the study, the activity does have an effect, although Robert McConnaughey, also involved in the study, said that the overall consequences on sea life aren’t clear.
In the short term, trawling has a “negligible” effects on the biomass, but long term effects are ambiguous.
“It’s clear, if trawls are used, there will be changes in…the habitats will be disturbed in terms of physical and biological characterizes,” said McConnaughey.
“If we think about management and what constitutes best practices there’s a number of key questions you have to think about.”
McConnaughey said that striking a balance between economic feasibility for fishermen while managing the fisheries in a way that will make them sustainable in the long term is complicated and difficult.
“We know trawling is an efficient way to fish and we need to feed the planet, so in that context it’s a very positive activity…for those that are responsible for protecting the integrity of these [habitats], virtually any change is unacceptable…I think in reality the answer is somewhere in the middle,” he said.