The Decline of the Firth of Clyde

The Firth of Clyde is a semi-enclosed expanse of water located on the west coast of Scotland which forms the mouth of the river River Clyde. The Firth of Clyde is around thirty miles across at its widest point and much of the firth is more than 100 metres (328 ft) deep, and a number of lochs open into the Firth.

Firth of Clyde

There are also around forty islands in the Clyde, although only a handful are inhabited, with the largest being the Isle of Arran. Today the Clyde remains an important deep-water port used by commercial vessels and cruise liners, while some shipbuilding and ship repair still takes place on the Clyde. There is also a significant Royal Navy presence with Britain’s nuclear-armed Vanguard-class submarines based at HMNB Clyde.

The Abundance of the Clyde

Fishing has been one of the most important parts of the Clyde economy for hundreds of years. Prior to industrial fishing, the area saw an abundance of fish species. Huge shoals of herring entered the Firth of Clyde, in turn attracting cod, ling, plaice, turbot, monkfish, rays, and skate (1). Blue sharks, basking sharks and various species of whales were also present.  This abundance of marine life saw the fishing industry around the Firth of Clyde grow throughout the 1700s and early 1800s, with the combination of abundant fish stocks and the relatively sheltered waters of the Firth creating the perfect environment for the fishing industry to expand. The main methods of fishing were purse-seining and the use of gill nets, trammel nets (2) and hooks and lines (3), with fishermen using sail-powered boats. This level of fishing was sustainable and the Clyde maintained its high levels of productivity. Fishing provided employment for thousands of people in the fishing industry and tens of thousands more in the related industries and supply chains, allowing the towns and villages around the wider Firth of Clyde area to grow and expand.

Trawling Ban Implemented, and a Thriving Herring Fishery

The development of steam-powered trawlers in the late 1800s led to the first concerns that the Firth of Clyde could become overfished. These vessels were much more powerful than the sail-powered fishing boats they replaced and could stay out at sea for much longer and fish in all but the very worst weather conditions. They also fished by dragging trawls over the seabed, a much more damaging form of fishing than the static nets and hooks and lines which had previously been used. In 1889 seabed trawling was banned in the Firth of Clyde by the Clyde Fisheries Board due to the damage it was causing to the seabed (2).

Commercially Caught Cod
Commercially valuable species – such as cod – were once abundant in the Firth of Clyde.

From the start of the twentieth century until the 1960s, the Clyde continued to produce vast amounts of fish, with the herring fishing industry providing the bulk of catches. During the Second World War, with most commercial fishing on the open seas severely curtailed, fishing could still take place within the sheltered Firth of Clyde, and the area produced close to half of Scotland’s entire herring catch (3). The herring fishery continued to provide plentiful catches and correspondingly high levels of employment in the years immediately after the Second World War. In addition, huge numbers of recreational anglers were attracted to the area every year, putting further money into parts of the local economy which were not directly related to fishing, such as pubs, restaurants, hotels and guest houses.

Herring Gone and Trawling Reinstated

In the second half of the twentieth century the Clyde’s herring catches began to decline due to the increasing power and efficiency of fishing vessels. The fishery had produced catches averaging between 20,000 and 40,000 tons up until the 1950s, but herring catches collapsed in the mid-1960s with less than 10,000 tons a year being caught (3). Measures such as a closed season for the herring fishery between January and March and catch limits were implemented but herring catches continued to fall. By the 1990s the total catch of herring caught in the Firth of Clyde was measured in hundreds of tons, and stocks were so low it could only support a fishery which was a fraction of the size of previous decades. While this should have led to an investigation into the cause of the decline and further action should have been taken to restore the stock, the opposite happened. To make up for the lack of mid-water herring the ban on trawling for seabed-dwelling fish such as cod, haddock and flatfish was rescinded, although trawlers were not allowed to operate within three miles of land (3).

The Decline Begins

The combination of trawling within the Firth of Clyde, along with the increasing efficiency of fishing vessels due to the switch from steam to diesel-power, electronic fish finders and seabed mapping and advances in net technology, meant that the area was fished at a new level of intensity. Bottom-dwelling demersal fish such as cod, hake, turbot, haddock, whiting and flatfish were now all being caught, while a smaller fishery for the remaining mid-water species persisted and used new techniques such as pair-trawling which were much more effective and efficient than previous methods (3).

By the 1980s stocks of cod, haddock and other seabed-dwelling fish were showing serious signs of depletion, with trawlermen struggling to catch enough fish to stay in business, while the herring fishery was also becoming less productive (3). This should have sparked both the Firth of Clyde fishing industry and politicians into action to protect the remaining fish stocks and allow both the fish numbers and marine environment to recover. Instead, the opposite happened. The ban on trawling within three nautical miles of the shore was lifted in 1984 (4) allowing the entire Firth of Clyde to be intensively trawled. While this provided a short-term boost to the now-struggling Clyde fishing industry it meant that remaining fish stocks were targeted and eventually fished out. Between 1984 and 2009 fish landing from the Firth of Clyde reduced by 99 per cent (3).

The decline of the Clyde’s fish stocks badly hit the angling community. The Lamlash Fishing Festival once attracted hundreds of anglers to the Isle of Arran (5). The record catch for the festival was set in 1967 when seven tons of fish were caught. This had dropped to around one ton by 1975, and by the 1990s the festival was producing under a quarter of a ton of fish. The Lamlash fishing festival has not been held since 1994 (6).

From Big Fish to Small Crustaceans

With the main commercially valuable fish species now absent from the Firth of Clyde, the fishing industry shrank dramatically with jobs being lost and boats decommissioned. Stocks of herring and whitefish fish were too low for commercial fishing for these species to be economically viable, so fishermen looked for a new species to catch. It soon became apparent that nephrops (a small lobster species also known as Norway lobster, Dublin Bay prawn and scampi) had dramatically increased in number across the Clyde as the fish species which preyed on them declined. Furthermore, the market for nephrops had grown significantly both in the UK and abroad, meaning that commercial fishermen could stay in business by switching to catching this species.

Nephrops now make up the majority of commercial catches in the Firth of Clyde.

Fishing for nephrops – along with smaller fisheries for prawns and scallops – came to dominate the Firth of Clyde. In 1986 fish catches still made up 60 per cent of landings by weight. By the 1990s this was down to under 40 per cent, and below 20 per cent in 2001. As fish landings rapidly declined nephrops catches steadily increased. In 2008 fish made up just 2 per cent of landings with nephrops, prawns and other crustaceans accounting for the other 98 per cent (7).

While this has allowed commercial fishing to on the Clyde to successfully continue, with around 120 nephrops trawlers operating in the region (3).  However, this came at a high environmental cost. While nephrops are considered sustainably fished in terms of numbers taken each year the methods which are used to catch them are highly damaging to the marine environment. Nephrops burrow into the mud and sediment, meaning that trawls which catch them dig into and churn up the seabed. This causes huge damage and has been shown to destroy organisms and structures on the seabed and, over time, alter the way the entire marine ecosystem functions. The heavy steel dredges which are used by the Firth of Clyde scallop fishery cause even more damage. A further, serious issue is that of discards. It is estimated that for every 1kg (2.2lbs) of nephrops that are caught, 9kg (20lbs) of other marine life is caught and discarded (3). This means that discard levels in the Firth of Clyde are at approximately 25,000 tons per year (3).

Finfish now make up only a tiny proportion of catches in the Firth of Clyde with nephrops dominating landings.

While commercial fishermen continued to catch nephrops the transformation of the Clyde began to make national news. A 2010 Sunday Times article titled Clyde Cleaned Out to Become Marine Desert said that the Clyde’s ecosystem was in “meltdown” due to the dominance of one species and the hugely damaging methods which were being used to catch it. Similarly, a 2013 article in the Scotsman titled Clyde Prawn Fisheries on Borrowed Time, drew on research carried out by the University of York. Dr Bryce Stewart, one of the lead researchers, was quoted in the article saying that the Firth of Clyde was “one of the most degraded marine environments in the United Kingdom” and that there were signs that a microscopic parasite was infecting nephrops on the Clyde. Known as ‘bitter crab disease’ the parasite can change the taste and texture of the crustacean species it infects. While Dr Stewart acknowledged that fishermen were still successfully making an income from the Clyde’s stocks of nephrops he warned that if the nephrops fishery was to “go wrong” then there would be nothing left for fishermen to catch. Charles Millar, director of the Sustainable Inshore Fisheries Trust, a Scottish charity which promotes the sustainable management of Scotland’s inshore waters was also quoted in the article saying:

“The Clyde prawn fishery really is in the last chance saloon. Although it provides lucrative rewards in the short-term, if stocks were to collapse, and there are international precedents, then the Clyde would be devoid of a material commercial fishery”

Advocates of commercial fishing point to the fact that there is still some fish in the area, but often neglect to mention that it is immature fish, mostly whiting which make up the vast majority of the Clyde’s fish stocks. A 2012 study found that 85 per cent of the total weight of fish in the Clyde was below the legal landing size (9). Sea angling still takes place in the Firth of Clyde but it is a shadow of former times, with dogfish and small whiting making up the majority of catches. Only the summer mackerel still arrive in anything approaching good numbers. The Community of Arran Seabed Trust (COAST) states that the following species are now so reduced in number that they are – in commercial terms – absent from the Clyde: herring, turbot, cod, whiting, plaice, saithe (coalfish), ling, hake, halibut, dab, angler fish (monkfish), flounder, skate and rays.

Recovery Attempts

From 2001 onwards, limited measures and regulations have been put in place to restore the Clyde’s fish stocks, but these have met with limited success and some surprising results. Trawlers have been prohibited from operating between mid-February and the end of April as this is the spawning season for species such as cod. Despite the damage to the seabed that they are known to cause, scallop dredgers and nephrops trawlers were not covered by the ban and were still allowed to operate (creel fishermen were also allowed to continue fishing) (10), cod stocks showed little sign of recovery.

In 2015 an application was made to establish a regulated fishery in the Firth of Clyde (11). This would create limit commercial fishing to low-impact methods such as diving for shellfish and settling creels and traps in some areas, while other forms of damaging fishing would still be allowed in the remainder of the Firth of Clyde. This type of regulated fishery would have allowed a more varied range of marine life to re-establish itself in the low-impact zones of the Firth of Clyde. In 2016 the Scottish Rural Environment Secretary Fergus Ewing said that the regulated fishery would not be implemented due to “practical difficulties in managing quota,” [issues with] “fleet flexibility,” and “a low level of support from those who would be directly managed by the regulating order.” The Scottish Fishermen’s Federation (SFF) welcomed the decision to reject the order (12).

Plans to ban fishing with creels and traps in the Firth of Clyde have proved controversial.

With the Firth of Clyde fish stocks still seeing no meaningful recovery new measures were finally introduced in 2022. The ban on bottom trawling was extended to include scallop dredgers and nephrops trawlers. Although they allowed these types of fishing to continue for almost twenty years, Marine Scotland (the department of the Scottish government which oversees Scotland’s Seas) stated that “during spawning, cod are extremely vulnerable to any activity impacting the seabed” and “minimise disruption to the spawning environment and harness cod reproduction” (13). The new limitations also controversially banned creels being set for crustaceans species, despite this being one of the most sustainable and least damaging forms of commercial fishing (14), although this was later partially reversed and creels were allowed to be used in some parts of the Firth of Clyde.

One conservation measure which has been put in place is the no-take zone (NTZ) in Lamlash Bay. This was established in 2008 after many years of campaigning from the local community. The zone covers around one square mile (2.6 sq km) at the northern end of Lamlash Bay on the Isle of Arran. No fish or shellfish can be taken from the zone and the surrounding shore area (6).

Lamlash Bay NTZ and Maerl C ArranCOAST
Lamlash Bay NTZwas established in 2008 and protects the maerl beds. Images © ArranCOAST.

The no-take zone also protects the maerl beds which are found in Lamlash Bay. These are a seaweed-like form of pink algae which provides a habitat for juvenile fish and other sea creatures, but due to the slow growth (which averages around 1mm a year), they are highly vulnerable to destruction by trawlers and dredgers. The no-take zone has been a success – lobsters and scallops are four times more abundant in the zone than in the areas surrounding it which are open to trawling, and seabed weeds and marine vegetation have also recovered and now provide a nursery area for juvenile cod.

There has been some positive, if surprising, recent news on fish stocks in the Firth of Clyde. In 2021 scientists found that the reduction of fishing pressure in the Clyde had seen sprat numbers increase rapidly (15). This was unexpected as it was believed that the herring which the Firth of Clyde was once famous for would return as fishing intensity eased. Dr Joshua Lawrence, the lead scientist on the study, told the Guardian:

“We’ve seen no recovery in the herring stock, as one would normally hope for following a reduction in fishing pressure. Instead, we have seen a huge increase in the biomass of sprat in the area” (15).

The reasons why herring have not returned, and sprat appeared to have taken their place, are currently not known. It may be connected to changing sea temperatures or spawning patterns, or it may simply be that herring numbers have been reduced to such a low level that even with reduced fishing pressure the species has been unable to make a recovery in the Clyde (15). The scientists who carried out the study warned that the replacement of herring by sprat shows that once an area has been overfished it does not necessarily return to its original state once fishing is reduced and that trying 555to restore the marine environment can lead to unexpected and unintended results. Dr Lawrence added that the most important factor should always be “ensuring stocks do not become overexploited in the first place” (15).

The Future of the Clyde

Herring Shoal
Herring were once the main species found in the Clyde, but have declined in number and have recently been replaced with growing numbers of sprats.

The fate of the Firth of Clyde is a sad story and one which mirrors Canada’s Grand Banks fishery. Both fisheries were once abundant but began to see a depletion of fish stocks due to overfishing. After multiple chances to reign in fishing intensity and allow the area to recover both fisheries collapsed, and both now rely on a single crustacean species – snow crab in the case of the Grand Banks and nephrops in the Firth of Clyde. Both areas can also be seen as an example of fishing down the food chain – the process of large, commercially valuable species being removed and fishermen then having to switch to a new, smaller species which was previously ignored.

The return of sprats to the Firth of Clyde is a small positive step, as is Marine Scotland’s belated decision to finally ban scallop dredging and nephrops trawling during the cod spawning season. However, much more stringent limitations on forms of commercial fishing that damage the seabed will be needed before the Firth of Clyde will see any form of meaningful recovery. It remains to be seen if Marine Scotland and the Scottish government have the will to enforce these changes.

Revive the Clyde is a campaign run by SIFT (Sustainable Inshore Fisheries Trust) which aims to work to restore the Clyde and help make the changes which will once again lead to the Clyde becoming a diverse and healthy fishery. You can pledge your support by signing the Clyde Charter by clicking here, and follow the campaign on Twitter and Facebook.


  1. Changes in the Firth of Clyde Ecosystem Since 1850, R. Thurstan.
  2. Howard Highlights the Hey-Day of Clyde Fishing, The Arran Banner, 18 Jan 2020.
  3. Ecological Meltdown in the Firth of Clyde, Scotland: Two Centuries of Change in a Coastal Marine Ecosystem, Ruth H. Thurstan, Callum M. Roberts, 29th July 2010.
  4. Sea Change: The Three Mile Limit, Coastal Communities Network Scotland, 3rd January 2019.
  5. Scott, K., Arran Community Imposes No-fishing Zone, The Guardian, 7th February 2008.
  6. No Take Zone: Lamlash Bay, ArranCOAST.
  7. Figure 15, Plos One.
  8. Clover, C. and Smith, L., Clyde Cleaned Out to Become Marine Desert, The Sunday Times, 11th July 2010.
  9. ‘Signs of Recovery’ for Fishing in Firth of Clyde, BBC News, 19th June 2012.
  10. Editor, Gougeon Says No Plans to Amend Seasonal Clyde Cod Spawning Closure, The Fishing Daily, 3rd March 2022.
  11. Report to the Scottish Parliament on Orders Regulating the Management of Shellfisheries under the Sea Fisheries, The Scottish Government, February 2016.
  12. SFF Welcomes Decision to Reject Regulating Order Proposal for the Firth of Clyde, Scottish Fishermen’s Federation, 28th July 2016.
  13. Seasonal Clyde Cod Spawning Closure, Marine Scotland, 13th January 2022.
  14. Brown, H., Clyde Fishing Ban: ‘No scientific Evidence of Creel Fishing Impact on Cod Spawning’, Says Professor as Fishermen’s Struggles Continue, The Scotsman, 3rd March 2022.
  15. Richardson, H., Clyde’s Fish Stocks Start to Recover – With a Different Fish Than Before, The Guardian, 7th October 2021.