More food for the debate on scallop harvesting (post no 2)

Dear all

The debate continues and your blogger, for one, is learning so much. Methinks we will need to have a public meeting to share visual material and knowledge, insights and ideas.

For now, here's the next contribution – items in angular brackets have been inserted by Margaret Powell-Joss, your blogger.

Is Scallop dredging Sustainable?

by David Ainsley

In his recent posting, D[.F.] states that he is fishing the same grounds that he fished 30 years ago and making a profit. He argues that this means that he is fishing sustainably – but he has not considered the damage that dredging causes to seabed communities and the evidence of declining scallop spawning stock biomass and recruitment.

Scottish scallop landings by UK vessels have risen from less than 2000 tonnes in 1974 to around 8-10,000 tonnes from 1994 to 2008. The 2008 figures are about 10% down from the peak.

The spawning stock biomass was just over 5000 tonnes in this area (North West management area) in 1999 but in 2007 – the last year for which figures are available – the SSB was at the lowest historic level of just over 1000 tonnes.

Both West coast of Scotland scallop management areas are shown in red on the chart on the report as spawning stock biomass and recruitment are declining [ref (1)].

But measurements of spawning stock biomass only go back to 1981. We know that seabed communities have been subject to damage by steam trawlers since the 1870’s – dredging started much later. In order to decide how healthy a stock is, we need to know what the historic stocks were before fishing began.

One way to do this is to look at all the old records, and the book The Unnatural History of the Sea by Prof. [Callum] Roberts takes this approach [ref (2)]. One scientific study estimates that only 10% of the fish swim in European waters that were present in the year 1900. But by 1900 stocks had already been industrially fished, so the real figure may be 5%.

Another approach is to close areas to fishing and monitor what happens to stocks. By 2006, the first Isle of Man closed area, protected for 20 years, had scallop biomass levels at more than 60 times those shown prior to protection [ref (3)]. Stocks have since continued to increase. There is strong evidence that this has led to greater returns from adjacent fishing grounds.

So catches remain high, but spawning stock biomass and recruitment are at dangerously low levels.

Why has this happened? There are a number of reasons:-

- In the early days, solid dredges were used in open areas like Luce bay. The solid dredges gave way to Newhaven dredges with spring-loaded tooth bars designed to work rough ground. This, combined with advances in electronics, allowed boats to work previously un-fished grounds.

- In the old days Decca was used for navigation. It relied on a land-based signal and, like mobile phones, there were many areas where it didn’t work well. Now we have stunningly accurate GPS, plotters, side-scan sonar, 3-D echo-sounders, systems such as Roxanne, which reveal very bit of suitable ground, allowing all those little bits nobody knew about before to be fished out. Scientists call it technological creep - in recent years it has been more of a technological gallop.

The scale of the ecosystem damage is obvious to those of us who have dived here [in the Firth of Lorn and further along the West coast of Scotland] over the last thirty years. Until the mid-eighties we never used to see sea-beds damaged by dredgers, but – as technology improved over the years – the dredgers worked right up to (and sometimes over) the reefs. It is now difficult to find a piece of seabed suitable for dredging that has not been dredged. To find such areas, you need to go to Norway, where they do not dredge and have miles of mussel beds and other healthy sea-beds, supporting healthy ecosystems – if anybody is interested, I have film to show this.

Dredged sea-beds are less efficient as settlement areas for small scallops and as nursery areas for fish. Thus dredging affects fish stocks and, by association, the porpoise, dolphins, seals and whales which feed on them.

What scientists call the Alee effect applies: as scallop spawning stock biomass declines, the individuals left become generally spaced further apart. There comes a point at which the individuals are so far apart that the gametes rarely meet, and recruitment declines, as is the case now.

As David [Frazer] correctly pointed out, the recent closed areas in the Isle of Man were closed with the participation and support of the fishermen. This is because they can see that having closed areas works to restore stocks. A survey in the Isle of Man showed that 85% of respondents are in favour – or strongly in favour – of Marine Protected Areas. There has also been huge support for the Marine Conservation Society’s campaigns, Your Seas Your Voice and Marine Reserves Now.

There is a legally established Public Right to Fish, and it follows that the public have a right to require that their fish stocks are fished in a sustainable way. If the damage caused by dredging happened on the side of the road where people could see it, there would be an outcry. People are now becoming aware of the state of the seabed and fish stocks.

We currently have an unfair situation where the very large percentage of the owners of the stocks who wish to have areas closed to allow fish and shellfish stocks to regenerate currently have only 0.006% of UK seas fully protected.

Dredgers are decent people. But if there had never been dredging, there would almost certainly be opportunities for other fisheries, and the seabed would be much healthier, as in Norway.

The Firth of Lorne is closed to dredging, but divers – who harvest scallops without damaging the seabed – can still operate. If an area were closed to all fishing, scallop stocks could rebuild and seed other areas, as happens in the Isle of Man.


Ref (1) Steven Keltz, Nick Bailey (Sarah Heath, ed), Fish and Shellfish Stocks, Crown copyright, 2010. marinescotland science. pp63-66. [link takes you to pdf version for download]

Ref (2) Callum Roberts, The Unnatural History of the Sea: The Past and Future of Humanity and Fishing (Gaia Thinking), Washington/Covelo/London: Shearwater Books/Island Press, 2007.

Ref (3) BD & JS Beuchars-Steward, Principles for the Management of Inshore Scallop Fisheries Around the UK, 2007. [link takes you to quickview of pdf document]