The recent story of Clyde fish is summed up in one, frequently-shared graph originally published in the Scottish Government’s Clyde Ecosystem Review in 2012. Though not up to date, it does tell a story of how the Clyde reach its current point, in terms of fish populations: one of the rise and collapse of whitefish landing, and the parallel rise of the nephrop or /prawn fishery.
The Ecosystem Review came hot on the heels of Ruth Thurstan and Callum Roberts’ 2011 paper, Ecological Meltdown in the Clyde, which told a story of a decline in fish landings from the 1880s, which was moderated by closures, but accelerated when a three-mile limit on trawling was removed in 1984.
In a 2021 paper, Paul Fernandes and Joshua Lawrence described the Clyde as “one of the most anthropogenically impacted marine environments in the world”.
"Overfishing," it said, "throughout the latter half of the 20th century brought about the collapse of these traditional 'finfish' fisheries, and these have now been replaced with a fishery for prawns. This is an example of fishing down the food web."
There are many other graphs that tell a similar story. For instance, the following, of catches from the Lamlash Fishing Festival which dramatically declined and never recovered.
What about quotas?
Part of the story not told in the Clyde Ecosystem Review graph is that of quotas, and many fishermen point out that the low landings are at least in part due to quotas or total allowable catches (TACs), which are themselves calculated through stock assessments and modelling. The following graph shows the agreed quotas advised by the International Council for the Exploration of the Sea for the West of Scotland since 1987.
Are cod being impacted by climate change?
A comment frequently made by fishermen is that the cod are leaving in pursuit of colder waters because of climate change - and there is evidence to suggest that cod have shifted polewards with rising temperatures, but the distribution of the shift is complex.
One study published earlier this year titled 'Variable trends in the distribution of Atlantic cod (Gadus morhua) in the Celtic seas' found that the West of Scotland stock “significantly increased in latitude and longitude over time, indicating that the distribution of cod there moved north and east, towards the North Sea”.
Is there less life in the Clyde than in the past?
Not according to the Scottish Government’s Clyde Ecosystem Review. It said: “The biomass of fish in the Clyde is the same, or for some species more, than when intensive fishing started... However, the community of fish is now made up mostly of small fish, and mostly small whiting.”
Are nephrops trawlers responsible for the loss of cod and other whitefish?
Various studies have looked into this. Was it that nephrops populations grew because the whitefish that ate them had been overfished? Or is it that nephrops trawling itself is impacting the cod populations? Two ways in which it has been suggested that bottom trawling could be impacting on cod populations is through damage to their nursery grounds and by cod moralities in their bycatch.
It is only recently, however, that a study of cod landings and observer monitoring data produced a model that shows that even the small levels of bycatch caught by nephrops trawlers appears to be impacting the recovery of cod populations. The following graph, originally produced by the Scottish Parliament (SPICE) illustrates this.
Is there a bycatch or discard problem?
A full discard at sea ban came into place in the UK in 2019, following a phased introduction that started in 2015
An observer programme, jointly operated by the Marine Directorate and Scottish Government, collects data on bycatch at sea, recording species, size and quantities. What a graph it has produced reveals is that the quantity of cod in bycatch by nephrops trawlers (the grey blocks) is so small in the West of Scotland it does not even register for 2023.
However, it should be noted that though the Clyde sea is one of the most intense areas of nephrops fishing, there were no observer trips in the area in 2023.
In 2019 an Open Seas article examined the question of whether discards at sea, though banned, were still happening. Their calculations revealed a difference between expected landings and the actual landings data. This suggested either bycatch had reduced naturally or had been reduced by gear modifications, or that some discards were happening at sea.
This Open Seas calculation is now relatively old. However bycatch data since has revealed a continued decline in nephrops trawler bycatch.
How has the Clyde fishing flee changed?
The Clyde fishing fleet is reported to be aging faster than other Scottish fleets. It has also shrunk dramatically with many families, who have fished for generations, leaving the industry. Graphs published in the Clyde Fishermen's Trust report A Vision: The Clyde Fishery illustrate this shift.
The number of vessels had also decreased.
Are the cod in the cod box?
Clyde fishermen will often say that one of the problems with the closure area is that the cod are not there. They are not spawning in the box. But what does the science say? The problem is that the research on this is fairly old.
The area is one that in the past (1980s and earlier) cod did annually congregate in, attracting an intense fishery, with vessels arriving from Ireland and elsewhere. But, according to Professor Michael Heath, the cod box was never the only place that cod congregated to mate. “There were other smaller areas on the Clyde as well, that are well documented from fishing data and also from plankton surveys to map the distribution of cod eggs in the water.”
Current data on cod in the box is sparse and amounts to only a few sample trawl tows by Clyde Fishermen’s Association vessels.
Are there other areas that should be closed or protected?
One suggestion being made by some campaigners and scientists is that what are often called nursery grounds, where young cod can be found, which are mostly in shallow rock areas, near kelp forests and seagrass beds. The habitats cod uses are vulnerable to damage by trawling.
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