“The pervasiveness of the influence of bottom trawlers on the Gulf of Mexico is evident in these images from NASA’s Landsat satellite. Showing two different areas of a single scene captured on October 24, 1999, the images reveal dozens of mudtrails streaking the Gulf in the wake of numerous trawlers, which appear as white dots. The amount of re-suspended sediment dredged up by the trawlers gives the water a cloudy appearance.
Read more at: http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17668
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Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
As this picture was taken in October 1999 and it is now June 2007 can we assume that this is the worst case to be observed in the past decade? More than likely. Lets see 24 October 2000, 2001, 2002, 2003, 2004, 2005, and 2006. And then lets see 24 January, Feb etc, for each of those years so we can assess the relevance of this photo.
A picture tells a thousand lies.
The mud trails pictured are interesting but are not indication of any detriment. The intense turbid area to the lower left centre in the upper picture is typical of that produced by large schoals of bottom feeding fishes such as mullet, croakers and Australian salmon. They play an important role in releasing nutrients trapped in bottom sediments. Trawlers do this as well.
The trails stirred up by the nets themselves are not very intense. Most of what is pictured probably comes from propeller wash. Similar trails can be seen in many satellite images of the Florida Keys where they are caused by larger yachts not towing any nets.
Such trails are most apparent when the water is calm and clear. Most of the time they are masked by natural turbidity stirred up by wind waves.
” They play an important role in releasing nutrients trapped in bottom sediments. Trawlers do this as well.” – Walter
Claim: from the bottom trawling industry :
Bottom trawling is like farming : it “tills” benthic sediments , enchancing overall productivity.
Fact: Bottom trawling is more closely analogous to forest clearcutting than to farming because both practices completely remove habitat structures that can take centuries or more to regrow.
Besides removing target species , trawling scrapes away corals, sponges and other organisms that provide spawning grounds and nurseries for juvenile fish.
Ann,
You are quoting third party assertions. I am speaking from direct observation. Do you have any experience in trawling? Have you ever ridden the headrope of a trawl underwater and seen what it actually does? The trawlers pictured are operating on sediment bottom. No corals or sponges are present. There is not even a remote analogy to forest clear cutting.
Hi Walter,
I think we have all heard the sort of things Ann is talking about. Do you mean that only the type of trawling in the type of areas pictured don’t do damage (and in fact are beneficial), or do you think all trawling is OK? As you have had experience with this, it would be interesting to read your views.
Hi Walter,
And btw , thanks Jennifer for posting this important thread.
Walter, I’m actually a bit informed on the bottom trawling issue as I did a work for Greenpeace International and an Estonian NGO on a bottom trawler, the Lootus II, that is operating on the high seas outside the Grand Banks and up in the Spitsbergen area.
I sure know exactly how a bottom trawling net looks like.
Deep-sea bottom trawl fishing vessels drag huge nets armed with steel plates and heavy rollers across the seabed.
It was a bit unfortunate that the sponge communities and corals were mentioned in my above quote , but I have seen what bottom trawl nets are doing on sediment beds as well from video footage. Not much is left…
The BT industry often claims that they are trawling on sediments without sponge communities and corals and this will be like ploughing a field..
However, what is dangerous with bottom trawling is that they are moving to new and deeper areas as soon as they have destroyed an old one..
They banned trawling for scallops in Port Phillip Bay because it was screwing things up for the eco-system. That was good, but now the Japanese sea stars have turned up, along other pests.
Trawling encompasses a wide range of equipment, habitats and environmental impacts. My comments apply specifically to what is pictured, i.e. coastal shrimp trawling in the northern Gulf of Mexico and to coastal paenid shrimp trawling generally. It is in no way comparable to the destructive and unsustainable deep sea trawling industry. Equating all trawling as highly destructive is simply ignorant. It’s like wanting to ban all vehicular use because a Caterpillar D11 can be so damaging in a flower garden.
Hi Walter,
Thanks for condemning deep seas bottom trawling…
Bottom trawling is one of my pet hates. In a previous life (i.e. before kids) I was a keen diver and I saw the effects.
Over sandy bottoms there probably is not much damage – but the real issue is that over any other kind of bottom – the weeds, sponges, corals etc get trashed. And these tend to be the nurseries for lots of fish… Anyone notice how the cost of fish is skyrocketing?
The deep sea trawling is probably the worst as the bottom can take literally centuries to recover from the effects of a “shot”. And with the modern equipment available today, areas previously too “equipment destroying” to fish get exploited now. Steve O’Shea (the Kiwi squid guy) is really aginst it. At the TONMO forum, he regularly has posts that highlight the damage. I can’t vouch for the veracity of these pictures – but as I said, I have personally seen simmilar.
http://www.tonmo.com/forums/showpost.php?p=48707&postcount=45
The other issue I have with this is the waste of the by-catch. It just gets dumped back into the water becasue it’s not commercial… very sad.
But I guess we all have to eat.
http://www.newscientist.com/article.ns?id=dn7947
cheers
Arnost