Causes of change
Major changes to the Firth of Clyde ecosystem
In the 1880s, it was estimated that 500,000 people in Scotland were involved in the fisheries in some form, either as fishers, gutters, curers or for the supply of boats and gear[i]. By this point, the fishing industry in the Clyde had already had a substantial impact on the marine ecosystem. The fishing grounds were frequently referred to as ‘exhausted’31, and references were commonly made to the diminution of species25, 36. By 1890 there was already a feeling that the Clyde fisheries (except perhaps for the herring) had passed their greatest productivity.
Important technological advances occurred in the Clyde throughout the end of the 19th century, until the latter half of the 20th century. Within this time, the scale of transformation of the Clyde ecosystem was extensive. By the 1960s, the famous herring fishery had suffered severe declines, and even improved technology could no longer find enough herring. The same pattern occurred for demersal species once the herring had gone, but the rise and fall of these fisheries took a much shorter period of time. This was probably because of the many previous years of fishing pressure, and the large catches that could be taken quickly by very efficient gear.
The way these species were fished almost certainly contributed to their and other species decline, as demersal trawls and dredges are not selective and damage and destroy the habitats they are dragged through. Improved technology also left nowhere for the fish to hide, therefore few animals were able to reproduce to continue supplying the fishery. Those interviewed stated that declines in both the size and abundance of fish occurred as trawling increased (pers. comm.).
Boris Worm and colleagues recently investigated in to the declines of commercial fish populations and the impact this may have on ecosystem services[ii]. They classed fisheries as collapsed where there had been a 90% or greater decline from maximum catches. Records dating from 1960 will not record the maximum abundance of cod, haddock, whiting and other species, as these have been exploited for hundreds of years. Nevertheless, using the top recorded landings for each of these species in the 1960s, and comparing them to landings in the last couple of years, cod and whiting show declines of over 99%, and haddock over 95%. These fisheries are collapsed, and now commercially extinct.
These species are not yet biologically extinct, but they are ecologically extinct and no longer perform functional roles in the Firth of Clyde ecosystem. This environment is now less biologically complex and with much lower abundance of species and is therefore less resilient to environmental fluctuations[iii]. This decline of fish in the Firth of Clyde may in part account for the success of the Nephrops and scallop fisheries which target species subject to much reduced predation pressure, increasing population sizes.
The transformation of the Clyde has been swift and may be irreversible if current practises continue. The fisheries of the 19th century concentrated on herring but also included many diverse fisheries for demersal and invertebrate species. Today, the composition of main species fished has changed greatly. Fish no longer dominate catches, and invertebrates from the bottom end of the food chain are the main species fished today.
Figure showing the relative proportions of species landed in the Clyde from 1987 to 2006. Nephrops now dominate catches, and other invertebrates have increased. The proportion of finfish has lessened to less than 10%. Source: SFPA.
Figure showing the quantities of groups of species landed in the Firth of Clyde from 1987 to 2006. Overall landings peaked at nearly 8000 tonnes in 1992 but have since decreased. Flatfish landings have become insignificant and roundfish have greatly declined in the last 6 years. Invertebrates dominate catches. Source: SFPA.
The value of Clyde fisheries is now mainly supported through Nephrops catches, which contributed 85% of the Clyde’s total fisheries value in 2006. This contrasts greatly with Clyde fisheries at the turn of the century, when herrings dominated the composition and value of catches, taking 81% of the value in 191348.
Figure showing the value of landings of groups of species landed in the Firth of Clyde from 1987 to 2006. Nephrops dominate landings by value. Source: SFPA.
Why has this transformation occurred? A global perspective
The origins of intensive exploitation of fisheries for herring and cod can be traced back to 1000 AD when there was a sudden expansion of marine fisheries, thought to be due to urban population growth, an increase in agriculture and the subsequent decrease of freshwater resources[iv]. By the twelfth century, herring and cod were being cured and widely traded. The early development of the east coast of North America from the 15th century was based on the trade in cod, whilst in northern Europe herring became a staple food during lean winters[v].
From the mid-1800s the industrial revolution concentrated a growing population in the cities, increasing demand for food91. Much of this was from the sea, as transport expanded and improved, and the use of ice increased to preserve fish on their journey from expanding fishing grounds to inland populations[vi].
Technological improvements continued throughout the early 20th century as diesel engines came into use, enabling fishers to travel further out to sea, or surround shoals of fish faster with their nets and prevent fish from escaping[vii]. Synthetic nets came into widespread use by the 1950s, which were much stronger and allowed the scaling up of fishing activities93, as did the invention of rock-hopper gear in trawls a few years later. Innovations in technology, coupled with a rise in effort led to a dramatic growth in fisheries, and global landings rose from 19 million tonnes in 1950 to 64 million tonnes in 197093. This rise in catches continued until the 1980s, when despite the fact that efforts continued to increase, landings declined[viii]. This was not noticed until much later however, because of massive over-reporting from China94.
It has only been in recent years that people have started to understand the major changes that have taken place within marine ecosystems due to human influences. People rarely see the harm that is being caused by human activities, as it is hidden underneath the surface of the sea. Another reason for the lack of understanding is that historical changes to the marine environment have rarely been documented, or, if references do exist, these are taken as anecdotal and assumed to be exaggerated3. It is easy for people to fail to appreciate changes in abundance and size of marine species because of the ‘shifting baseline syndrome’, which was described by Daniel Pauly[ix]. This is where each successive generation comes to see the current status of fish stocks as the baseline for a normal abundance.
Changes in people’s perceptions of what is natural, can therefore take place extremely rapidly. The fluctuations that are so often seen in marine populations also have a hand in buffering our ability to see gradual declines and changes. Descriptions by past fishermen and anglers then become fanciful tales that seem as if they could not possibly have been true. Rapid changes in environmental baselines have been shown by Saenz-Arroyo and colleagues[x] for fishers in the Gulf of California, where young fishers failed to appreciate the sizes and abundances of fish quoted by older fishers. The fact that baselines have shifted so rapidly, emphasises the importance of taking into account those few ‘anecdotal’, qualitative references that we have of past oceans, and using these to determine how much marine ecosystems have changed through human influences.
Possible sources of bias
Fishery statistics had to be taken from a few different sources covering slightly different areas in the Firth of Clyde. However it was felt that the statistics were still comparable because the data regions did not change to a great extent over the years.
Questionnaires were to be conducted to assess people’s perceptions of the changes to the Firth of Clyde ecosystem (see Appendix 1). However, I experienced a few difficulties when trying to contact fishers. I was only able to contact 8 people, and I did not believe that this constituted a representative sample. While the questionnaires were unable to be used in any statistical analysis, people’s comments and views were included.
Regrettably, when trying to contact other fishers through the Scottish Fisheries Federation, the links with York University essentially halted my investigation, and I was not able to contact anyone who may have had important views on the reasons behind the declines of finfish in the Clyde. This is unfortunate, as whilst some people may mistakenly feel that their views would be either misrepresented or disagreed with; without their input, their views cannot be represented at all.
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[ii] Worm, B., Barbier, E.B., Beaumont, N., Duffy, J.E., Folke, C., Halpern, B.S., Jackson, J.B.C., Lotze, H.K., Micheli, F., Palumbi, S.R., Sala, E., Selkoe, K.A., Stachowicz, J.J. and Watson, R (2006). Impacts of biodiversity loss on ocean ecosystem services. Science: 314: 787-790.
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[iv] Barrett, J.H., Locker, A.M. and Roberts, C.M (2004). The origins of intensive marine fishing in medieval Europe: the English evidence. Proceedings of the Royal Society of London B 271: 2417-2421.
[v] Valdimarsson, G. and James, D (2001). World fisheries – utilisation of catches. Ocean & Coastal Management 44: 619-633.
[vi] Roberts, C.M (2007). The unnatural history of the sea. Island Press, Washington DC, USA.
[vii] Valdemarsen, J.W (2001). Technological trends in capture fisheries. Ocean & Coastal Management 44: 635–651.
[viii] Pauly, D., Christensen, V., Guenette, S., Pitcher, T.J., Sumaila, R., Walters, C.J., Watson, R. and Zeller, D (2002). Towards sustainability in world fisheries. Nature 418: 689-695.
[ix] Pauly, D (1995). Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology and Evolution 10: 430.
[x] Saenz-Arroyo, A., Roberts, C.M., Torre, J., Carino-Olvera, M. and Enriquez-Andrade, R.R (2005). Rapidly shifting environmental baselines among fishers of the Gulf of California. Proceedings of the Royal Society B 272: 1957-1962.
