Pat Gowen – Offshore aggregate dredging: do fish campaigners realise the damage it causes? – Mar 2013

Thanks for hunting and finding that paper on seabed recovery at http://www.cefas.defra.gov.uk/media/463535/monograph2-web.pdf

Sadly, after struggling for half an hour, my wretched machine was only capable of displaying the first page, e.g. the headings. I just don’t get on at all well with PDF files.

I dared not pursue for longer, as my time is fully occupied with masses of concerns over the recent massive escalation of coastal erosion here in Norfolk and Suffolk.

I wonder if I dare suggest that you write an item for our website on this issue using the latest CEFAS material ? It would be of great interest to our readers. If you could submit such to our MARINET editorial scrutiny group via Stephen it would really be appreciated.

We could do with some items from more dedicated experts such as your good self anyway.

Interesting…

There’s a more up-to-date review of recovery of the seabed following dredging at http://www.cefas.defra.gov.uk/media/463535/monograph2-web.pdf. It indicates that recovery does occur, albeit over a variety of timescales depending on local conditions. This seems to run contrary to what the fishermen say, however, the reference discusses recovery of seabed faunafauna The animals characteristic of a region, period, or special environment rather than fish. Could it be that the dearth of fish is simply due to the massive over fishing that has occurred in recent decades?

Finally, it seems a bit simplistic to compare the experience of such a site specific, targeted, and highly managed activity such as oyster fishing with the more random, wide scale and opportunistic activities of the offshore mobile gear fleet. In my view not a good analogy…

I may contact Cefas – sounds like they may have more information to share.

You will have seen the areas licensed for aggregate dredging in the articles I listed earlier, and also the CEEFAS three and four year post dredging findings at
http://www.marinet.org.uk/campaign-article/cefas-centre-for-environment-fisheries-aquaculture-science-find-no-recovery-of-eco-system-damage-after-offshore-dredging from the Wallingford/CEFAS paper at http://www.marinet.org.uk/wp-content/uploads/Assessment-of-the-Rehabilitation-of-the-Seabed-following-Marine-Aggregate-Dredging.pdf

It might not be a bad idea to contact CEFAS to ask them if they have looked at the same areas since.

Of course, up to now, apart from a few exclusions, e.g. prohibition due to navigational dangers, military exrcises, etc. fishermen may fish as they will where they will, so the actual floor areas covered could be far greater than that allocated for dredging.

The latest report I have from the (few remaining) local fishermen is that the areas aggregate dredged well over twenty years ago are still as dead as the proverbial Dodo, but apparently dredge fishermen, such as the Oyster gatherers at West Mersea, visit the same areas with a productive degree of success time and time again.

Do let me know what CEFAS says. They are usually quite good with their replies. It might spur them to look at the same areas again so to provide the answer.

I was really just trying to get some clarity as your original post seemed to imply dredging was occurring over vast areas of seabed – actually, it seems that is not the case.

You still imply that there is a lack of recovery of the seabed after dredging – it that really the case? I’ve checked out your suggested reading and, not surprisingly, it shows that dredging does affect the seabed, but the indication is that recovery does occur once dredging has stopped.

Good luck with securing funding for the submarine!

It appears that we have been talking at cross purposes and that whilst you are naturally concerned over the impact of trawling damage over the wider areas, I was referring to the greater severity of the damage resulting from marine aggregate dredging at any one area and the lack of recovery due to this.

Thanks for bringing the Oxford Journal paper to my attention. Some excellent statistical information in that.

I wish MARINET owned a submarine !

I’ve just been doing a search and this might be of interest:

http://icesjms.oxfordjournals.org/content/64/3/453.full.pdf+html

It states that fishing affects 5.4% of the UK continental shelf (and may be as high as 21.4%) whilst the most extensive effect of dredging – plumes – only affects 1.2%.

Thank you – that’s interesting. I had hoped though that you could provide more information to qualify the point you made about aggregate dredging affecting a greater extent of seabed than fishing.

Also, you said the damage from aggregate dredging was irreversible. Are you saying that recovery of the seabed never occurs after aggregate dredging?

The reasons that offshore aggregate dredging is far more invasive and damaging than scallop or other bed trawling is because it sucks up large complete areas of sand to a depth more that sufficient to uproot the embedded sea floor flora, take up all the entrained fish and shellfish, molluscs, everything in fact, and further smothers downtide sea areas with the wash-off debris and silt that is washed overboard to leave the gravel and cohesive grit and sand as cargo in the hold to take to port. It leaves behind a marine desert that does not recover even after twenty years, in the same way that removal of your garden topside would leave a sterile area.

On the other hand, scallop dredging and chain dredging only scrapes the sea bed surface, bruising but leaving much of the flora bruised and damaged but still rooted so as to permit regrowth. Much is only rolled over. Smaller molluscs, fish, etc. can escape between and around the rakes as powerful suction is not used. That’s quite bad enough, but recovery soon follows.

There are our pictures of the seabed before and after aggregate dredging to be seen in our briefing at http://www.marinet.org.uk/campaign-article/marinet-briefing-paper and more in the CEFAS pages to be located by first going to http://www.marinet.org.uk/campaign-article/cefas-centre-for-environment-fisheries-aquaculture-science-find-no-recovery-of-eco-system-damage-after-offshore-dredging

For fine detail evidence also please go to the following:

http://www.marinet.org.uk/wp-content/uploads/entrainment.pdf as well as http://www.marinet.org.uk/campaign-article/seabed-recovery-following-dredging and see our video at http://www.marinet.org.uk/campaign-article/marinets-video-on-the-impact-of-offshore-aggregate-dredging-2

There are many more items on our website Marine Aggregate Dredging that should fully convince you.

Thanks Pat – I look forward to hearing from you.

An explanatory reply is on it’s way to you. I’m sorry for the long delay but it entailed much hunting for the evidence !

Pat – interesting points. I’m wondering though, by what measure do you conclude that trawling and scallop dredging results in a less extensive effect on the seabed than aggregate dredging?