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The blue marble

Supertrawler banned just as new evidence of trawling impacts emerge

News that the Dutch owned “Abel Tasman” super trawler may have to leave Australian waters after the lower house passed laws to freeze its operations for at least two years is well received. Allowing the operation of the super trawler with current uncertainties on impacts would have been irresponsible.

Just last week, the publication of a paper by Spanish scientists in Nature provided evidence of major impacts and long lasting effects of trawling on the sea floor. This paper looked at bottom-trawling boats - a different method to that used by the mid-water trawler “Abel Tasman”. But it showed how little we know about the damage fishing can do.*

Trawl fisheries has a long history, but it is a brutal practice. This perception is not a recent sentiment of environmental softness, as France banned trawling in 15th Century as a practice that destroyed productive marine ecosystems and was punished with decapitation. I recommend a precautionary approach to trawling, but do not recommend such stringent penalties!

This early awareness and extreme zeal, however, did not help conserve the French seafloor ecosystems on the long run.

France, through the IFREMER is one of the leading nations in the exploration of the ocean depths. Their fleet of advanced submersibles and ultradeep ROVs and submersibles able to reach 6,000 m like Nautile, has been used intensively in recent years to explore deep corals ecosystems.

Deep corals have been known to grow in Norwegian fjords for over a century. However, only recently, these fascinating coral ecosystems have been observed and explored in any detail. These deep-coral ecosystems grow on a cold, dark environment, and generate complex habitats that provide refuge for fish and invertebrates.

Deep coral ecosystems like that protrayed in this photograph once paved the shelf edge of all continents. Photograph: IFREMER, 900 m depth off the Atlantic French coast. Courtesy Dr. Sophie Arnaud-Haond.

As advanced technologies for deep sea exploration developed, deep coral ecosystems were found to be present along the continental shelfs and slopes of all continents, including Antarctica, forming a belt of coral that must have extended from 300 to 1,000 m depth along most of the 170,000 Km of shelf edge in the ocean.

But the initial excitement of these discoveries soon turned into concern as many of the corals discovered were completely trashed and devastated by trawlers. This was the fate of most of the deep corals that once paved the French Atlantic shelf edge, as French scientists discovered, with dismay, just last year.

Trawling has destroyed most of the deep coral ecosystems that paved the shelf edge of the Atlantic French coast. The smoking gun is still to be found. Photograph: IFREMER, 850 m depth off the Atlantic French coast. Courtesy Dr. Sophie Arnaud-Haond.

Seagrass meadows in the Mediterranean were also damaged and injured by trawling boats that left deep scars in the meadows and opened, as the attached acoustic image illustrates.

Side scan sonar image showing trawling scars, as parallel lines, in a 7 m Mediterranean Posidonia meadow. Courtesy: A. Marhuenda.

How many seagrass meadows and coral shelfs may have been lost to trawling before been ever observed or documented? Many of these ecosystems will never recover or will recover after centuries.

The ecological damages of trawling are devastating, but are far deeper than hitherto realised. The article just published last week in Nature by Puig and coauthors (“Ploughing the deep sea floor”) showed that trawling in the NW Mediterranean disrupted the sea floor and caused, when conducted along slopes, a destabilistion of the sea floor leading to intense erosive impacts.

As stated by one of the coauthors in an interview, trawling if the sea floor can be compared to plowing agricultural land. However, the key difference is that agricultural fields are plowed only once a year, whereas in many fishing grounds around the world the sea floor is often “plowed” every day. There is no chance of ecosystem recovery.

I do not advocate for an immediate end of trawling, but will like to see this damaging practice be phased out within my life span. We cannot just pretend we do not see, for now we have the technology to see the damage trawling makes. While trawling in the Aegean Sea in a study of red shrimp in the Mediterranean, my friends in the crew of spanish R/V García del Cid were devastated when the net emerged carrying one toilet. An ironic portrait of what we treat our seas like.

Fisheries should be sustainable or shall not be, for our future will strongly depend on our capacity to maintain healthy marine ecosystems. Industry, regulators and scientists must work side by side to this end.

*This paragraph was updated by an editor after publication to clarify the author’s meaning.

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