The Clyde fishery needs more reserves and less trawling

At this year’s Arran Agriculture Show the mission of COAST (Community of Arran Seabed Trust) to establish an angler and creeler friendly marine protected area received support from woodcarver Marvin Elliott. He had carved a big cod out of a piece of drift beechwood. “This wooden fish is meant to be an eye-catching reminder of those days of Lamlash Fishing Festival. This is the sort of size of cod that you used to be able to catch off our shores. Until we change our ways, our fish won’t be able to recover.” said Marvin.

Marvin Elliott's cod carved a big cod out of a piece of drift beechwood

COAST hosted a Marine Scotland talk from Dr Bill Turrell, Marine Scotland, and early in August the cod was on display next to Dr Bill Turrell during his talk at Lamlash Golf Club –“The Clyde Marine Ecosystem: is it in Meltdown?”  Bill is leader of Marine Ecosystems at Marine Scotland Science. He described the Clyde as a “marvellous inland sea” with 0.8% of Scottish Marine waters. The sea bottom has 9% gravels, 66% sand and 25% muds. It is a productive area in terms of algae blooms in March-April and September–October. The Firth of Clyde is warming, as much as a degree per decade.

The big changes in the Clyde are the types of demersaldemersal Living on the seabed fish (these live and feed on or near the bottom of the sea floor, which consists of mud, sand, gravel or rocks). The size of fish in the Clyde has radically changed. One-year old whiting now represent 72% of the fish present and 90% of fish are below minimum landing size.                                                                                                                                                                                                                    The Clyde has changed from an even mix of fish with many large predators to one dominated by just a few types and no large fish. Between 1920-1959 there were 13 species of demersal fish,including cod, saithe, haddock and hake and this had fallen to 4 species in 2000 and now is 9 species. It is clear that overfishing and types of gear have impacted on fish stocks. In 2010 VMS data of Scottish boats shows there were 66 prawn bottom-trawling boats, and 24 scallop dredgers with a total of 52,802 fishing hours. (That is without counting the Northern Irish boats and nomads that “turn up”. This summer there have been up to 40 Northern Irish trawlers in Campbeltown.)

Many of the 60 listeners had questions about what could be done, and why the Scottish Government had done little so far except for just 2.67 Km2 of No Take Zone in Lamlash Bay.  That took 10 years of campaigning by COAST to achieve. Bill has hopes for the future. In October a survey of pelagicpelagic The ecological area consisting of the open sea away from the coast and the ocean bottom. The pelagic zone contains organisms such as surface seaweeds, many species of fish and sharks and some mammals, such as whales and dolphins. Pelagic animals may remain solely in the pelagic zone or may move among zones. fish (these live near the surface or in the water column of coastal and ocean waters, but not on the bottom of the sea) will be done using acoustics. More research is needed. He is hopeful for the Clyde in the longer term as the bioproductivity is good, and with improved fisheries management over time there is a chance a mixed fishery could return.
For COAST, there are some areas that give rise to more questions and doubts about the conclusions of The Clyde Marine Ecosystem Report:

1. In the 1930s and 40s, the Clyde was not un-fished. It was intensively fished, but not by bottom trawlers, as this method was considered too damaging by the fishermen and regulators of the day to be permitted.

2. The evidence for lower fish biomassbiomass The amount of living matter. This is therefore a different measure to numbers of organisms. So, for example, there is much more biomass in 1 elephant than there is in 1000 fleas and there may be more biomass in 100 large cod than you would find in 150 small (because of over fishing) cod. in the 1930s and 40s than today comes with the huge caveat that the sampling was scanty to say the least. Their total survey effort amounts to 138 trawl tows over 83 years (1.7 per year on average). This means the error margins on the estimates will be massive. In effect, it is based on about one trawl tow per year in the early part of the time series, a sampling intensity that most would consider utterly inadequate to characterise the status of any ecosystem. While landings data tell you slightly different things from trawl survey data, the sampling intensity was much greater, amounting to thousands of tows for every year of the time series in the paper by Thurstan and Roberts (2010). Their confidence in what those landings are telling us is correspondingly much higher than the confidence we can place in the trawl survey data. That is not to say that the survey data are worthless. They give us an interesting and important insight into the state of the Clyde today.

3. The modern biomass, as the Marine Scotland report shows, is made up of very different fishes from the biomass in the 1930s and 40s. Many of the larger species – the ones that formerly sustained productive fisheries – are pretty much absent from the Clyde today, just as the Thurstan and Roberts paper indicated based on landings data. If they were still there, we’d be catching them. 70% of the biomass today, as they point out, is made up of <1 year old whiting. Interestingly, they feed mainly on planktonplankton Plankton is a generic term for a wide variety of the smallest yet most important organisms form that drift in our oceans. They can exist in larger forms of more than 20cm as the larval forms of jellyfish, squid, starfish, sea urchins, etc. and can be algae, bacterial or even viral down to as small as 0.2µm. They are nutrient and light dependent, and form the essential foodchain baseline for larger dependent aquatic lifeforms. Fish species rely on the density and distribution of zooplankton to coincide with first-feeding larvae for good survival of their larvae, which can otherwise starve. Man-made impacts such as dredging, dams on rivers, waste dumping, etc can severely affect zooplankton density and distribution, which can in turn strongly affect larval survival and thus breeding success and stock strength of fish species and the entire ecosystem. They also form the essential basis of CO2 take up in our seas ecosystem, hence Global Warming..

It seems to many of us, reports COAST in the October Newsletter, that they are filling a niche that was formerly occupied by herring and saithe in the Clyde. Therefore, comparisons of fish biomass between the 1930s and 40s and today is like comparing apples and oranges. If you want to understand the Clyde’s transformation more fully, you have to look at the change in the biomass of planktivores too. The evidence is very strong that the biomass of the plankton feeding fishes in the Clyde in the 1930s and 40s was much higher than today, so the ecosystem as a whole, almost certainly has less fish today than it did then (setting aside the criticism above about sampling inadequacy, which means the reliability of the biomass difference claimed is low).

Of course, the report is to be warmly welcomed for its positive message that the Clyde is not a write off (this was NOT in the paper by Thurstan and Roberts, but written by journalists in the daily papers). But the only way to bring it back will be to curtail the area over which prawn trawling and scallop dredging take place. What is needed is a network of well managed protected areas including core No Take Zones within broader angler and creeler friendly marine protected areas, a reinstatement of the three mile limit on dredging and trawling and serious effort control in all other areas.


Heath, M.R. and D.C. Speirs (2011). Changes in species diversity and size composition in the Firth of Clyde demersal fish community (1927-2009). Proceedings of the Royal Society, B, doi, 10.1098/rspb.2011.1015
McIntyre, F., Fernandes, P.G. and Turrell, W. R. (2012) Clyde Ecosystem Review. Scottish Marine and Freshwater Science Report, Volume 3, Number 3, The Scottish Government. Available on the website ISBN: 978 – 1 78045 -877 -9 (web only) pp.1-119
Thurstan, R. H. and Roberts, C. M. (2010) Ecological Meltdown in the Firth of Clyde, Scotland. Two Centuries of Change in a Coastal Marine Ecosystem. PLoS one, Volume 5, Issue 7, e11767 pp.1-14

Source: COAST October 2012 Newsletter,

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