The Clyde cod tragedy. Will once common fish ever recover?

The other reason for the absence of the cod supper is that it was never a favoured species at chip shops in Scotland, and still isn't now. Tiffany Irvin, at The Fish Works in Largs, observed “It’s only English people who ask for a cod supper. Scots always want the haddock.”

Still the fish on the menu at her popular shoreside restaurant tell us something. The only locally landed fish is langoustine, also often referred to as prawns or nephrops, which has now taken over as the big fishery in the Clyde. These two species, cod and nephrops, appear caught in parallel stories of rise and decline, a story visible in some of the graphs of fish landings.

Tiffany Irvin at The Fish Works in Largs serves langoustine landed fresh from the Clyde (Image: Robert Perry)

The Clyde cod once swam in great numbers. Landings of the fish peaked in the mid-1980s, with over 2000 tonnes in 1981, and steadily declined over the decades that followed, until, at the turn of the century there was no longer a fishery of cod or other whitefish in the Clyde.

Since then, cod has only been caught as by-catch by vessels hunting chiefly nephrops, which go under the more common names of scampi, langoustine or Dublin Bay prawns.

What has happened to the cod the Clyde is an issue of hot debate that raises questions about research and policy, and whether the Scottish Government is following, as it says it is, “the best available science”.

It touches on questions of how we value biodiversity and the populations of fish we eat and often call fish stocks, as well as what might be done to bring it back or why, beyond our bellies, we should care.

This graph, from the Scottish Government's Clyde Ecosystem Review (2012), shows the massive fall off in white fish landings, and in parallel a huge rise in Nephrops landings (Image: Scottish Government)

The Clyde cod box

The attempts to recover Clyde cod by closing off spawning areas to fishing became controversial, when, in 2022, the sudden announcement was made that an area known as the Clyde ‘cod box’, previously closed seasonally to whitefish trawlers, was now going to ban prawn trawlers, scallop dredgers and creelers.

This box at the south end of the Firth of Clyde, had previously been closed to whitefish trawlers, following  a report, in November 2000, by the International Council for the Exploration of the Seas (ICES) which stated that the cod stock in the West of Scotland was at serious risk of collapse.

ICES, in many of the years that followed, recommended a zero total allowable catch (TAC) quota for the fish in the West of Scotland - though what were issued were TACs that allowed for some cod to be landed as bycatch.

However, more recently, ICES advice for the north-western substock, including in the West of Scotland,  has shown a recovering stock, with the biomass now twice the size of the sustainable biomass threshold. In 2024 a total allowable catch of West of Scotland cod was agreed of 1,392 tonnes.

A genetically different fish

What also impacts Clyde cod management is research that shows that this local fish is genetically distinct, and therefore should be managed in separation from West Coast of Scotland stocks. 

Among those who see the Clyde cod as a discrete population, is Professor Michael Heath, an expert in the statistical modelling of fish populations at the University of Strathclyde.

He said: “For a long time, the whole of the West of Scotland was considered to be one cod stock, but as genetic analysis methods have become available, we’ve realised that cod are not just one big stock at all - they’re made of many sub stocks, with some exchange between them, more or less, depending on the areas.

“The International Council for the Exploration of the Sea (ICES) has recently reviewed all the evidence on west of Scotland cod populations from genetic, tagging, and bone chemistry. They concluded that although there may be some exchange between cod in the Irish Sea and cod in the Clyde, the Clyde cod are a distinct sub-population. There is very little evidence of exchange with the wider west of Scotland”.

"For example, if you look at the tagging data, very few of the cod tagged in the Clyde have been re-captured anywhere else outside the Clyde. They tend to stay in the Clyde and have developed a distinct genetic signature. That means that they’re a distinctive feature of Scotland’s biodiversity - and deserve protection.”

But has the box worked?

The Clyde cod box closure has been a key idea for preserving the species, though one that so far appears to have failed. It was initially triggered by the EU Commission, which in 2001, identified a “need for emergency and long-term measures to help the recovery of the cod stocks” due to “imminent danger of collapse”.

Such a closure wasn’t a new idea. Seasonal bans like these have been put in place around the world to prevent the possible over-exploitation of fish when they congregate at predictable locations  to spawn. However, a big question since has been whether the approach has worked.

A  2015 study by researchers from the University of Glasgow and Marine Scotland Science declared it “too little and too late”. There was no evidence, it said, that a seasonal closure of part of the Firth had led to local recovery of cod numbers or a reduction in overall mortality and the researchers noted,  “implementing spawning closures on nearly collapsed stocks may be why such measures often appear to have been ineffective.”

The cod box, however, continued as it was, until in 2021, the Scottish Government ran a consultation regarding the 2022/23 closure. The initial consultation supported a rollover of the limits already in place for many years.

So it came as a shock to fishermen when, following further consultation, the Scottish Government announced it was going to remove the exemptions for trawlers and creelers, to "maximise numbers".

Many fishermen, scientists and campaigners asked what the evidence was to back this decision, and criticised the manner of the consultation and rush through of the legislation.

Was the approach, some asked, being taken around minimising disturbance to spawning grounds, valid?

Some scientists argued that the problem was not so much with spawning disturbance, but cod bycatch in the nephrops trawl fishery. A response was issued by Professor Michael Heath on behalf of a long list of scientists, which said that benefits derived from “eliminating disturbance to mating behaviour” were likely “to be negligible and undetectable” and noted that “the justification for excluding creels from the cod box” was “lacking”.

It also pointed out: “Discarded by-catch of cod in the Nephrops trawl fishery appears, on face value, to be a potentially significant factor that could be limiting recovery of the stock. Cod by-catch is a very small proportion of the Nephrops catch weight, but appears to be a potentially significant fraction of the cod stock biomass.

The question of by-catch and the idea that nephrops trawling might be playing a role was not new - but only recently had research emerged to support it.

A study by Strathclyde University PhD student Ana Adao, controversially overlooked by the Marine Directorate on the basis that it was not yet peer-reviewed, was the first to show that a key factor impacting the cod population was the continuing levels of bycatch in the nephrops fishery.

Adao analysed several sets of data,  including the bycatch records made by observers sent out by the Scottish Fishermen;’s Federation and Marine Directorate on fishing boats and the landings of cod at fish market, and created statistical models.

PhD research by Anna Adao at the University of Strathclyde has shown that mortality of juvenile cod from bycatch is above sustainable limits.  (Image: Ana Adao, University of Strathclyde, SPICE)

Prof Heath, talking recently,  summed up what this data showed. “All the evidence suggests that cod in the Clyde are declining despite this spawning closure in the spring, and that it’s because they’re being caught in large numbers as bycatch by the prawn trawlers.

"The Scottish Government says that decisions are supposed to be made on the basis of the best scientific evidence. Here we have a solid piece of research, co-supervised by the Marine Directorate, which indicates that bycatch is plausible factor in the decline in cod, but the evidence is being ignored. On the other hand, we have the spawning closure which is supported by only circumstantial evidence, none of which has been gathered in the Clyde, with no evidence that it is having a positive effect.

Master fishmonger, John Watson, outside his shop in Largs (Image: Robert Perry)

"Why? The prawn fishery is a very valuable industry for Scotland and that should be a factor in the decision making too. However, there are measures that could be taken with the participation of Clyde fishermen, such as localised limits on trawling in places and at times when real-time bycatch data shows that cod are abundant, as has been done elsewhere. Surely that’s worth considering.”

Fishermen I spoke to have their own ideas about what is happening with the cod and the changing waters and fisheries of the Clyde. Some told me it was too late,  the cod were already gone, and that climate change was in part to blame. Some were sceptical about the modelling. Others talked of their efforts, and those by others, to fish sustainably and devise gear that catches vanishingly small amounts of cod. Many described a desire to be involved in collecting data to provide stronger science. But there are other proposals  too. 

For instance, Robert Younger, a lawyer for Fish Legal and Clyde 2020 believes that it would be sensible to close the northern half of the Firth of Clyde to damaging mobile fishing gears because that is where most of the cod nursery grounds are.  

A Scottish Government spokesperson said: “The Scottish Government has a duty to balance environmental and economic issues. The current approach reflects our commitment to maximise protection of cod and minimise their disturbance during spawning, while mitigating socio-economic impacts on our coastal communities.

Not the only fish

But the story of the Clyde is not only the story of cod.  Interestingly, there are positive stories around white, demersal fish. Professor Heath provides one. “Cod," he said, "have declined. But then haddock have increased in numbers. We don't really know why."

According to the Scottish Government's Clyde Ecosystem Review, the overall biomass in the sea is the same, but the ecosystem has changed, "with  the community of fish... now made up mostly of small fish, and mostly small whiting".

This should be of concern since what we see in the Clyde looks similar to a pattern, globally, which has been shown by research, of a shift towards populations of smaller fish. In the Clyde that appears as  more haddock and whiting than cod; more sprat than herring; more nephrops.   

Adult cod are among our bigger demersal fish, and can live for up to 25 years and typically grow up to 100–140 cm, or bigger. In 1970, famously, a record-weighing 46Lber was caught on the Firth of Clyde. Will we see such big cod, and such abundance again? 

Certainly, hatever solutions are pursued, it's unlikely fish shops will be full of Clyde cod anytime soon. Like Tiffany Irvin, John Watson, a master fishmonger in Largs, gets his cod, and most other fish,  from Peterhead. 

But the cod supper is not what counts most. It's the fish itself. The species may not be the only one in the Clyde, but it is a big fish that matters.