Scottish seas: what has changed ?

It is often said that Scottish seas are some of the most productive in the world. However, the reality is that much has been lost during the last 150 years as a result of more intensive fishing and use of destructive catching methods. Whilst overfishing is often seen as a recent problem, the signs of decline have been visible in Scottish waters for many years.

Until the 19th century, Britain probably had the richest natural oyster beds in Europe. The Firth of Forth contained the most important oyster fishery in Scotland during the 1800s, with oyster beds that extended 20 miles along the Forth. At the beginning of the 19th century, the oyster beds in the Forth were so productive that one boat could frequently drag up 6000 oysters in one day. However, from the mid 19th century, dredging for young oysters for export to beds around Holland and England, as well as an intensive local trade led to declines and the eventual commercial extinction of oysters throughout the Firth of Forth.

Other shellfish beds also suffered as a result of intensive dredging and collecting during the 19th century. Before Scotland embraced the otter trawl, many fishers used lines to capture large cod, skate and halibut. Bait was a vital part of this industry. During the late 19th century, greater line fishing effort, increased pollution in coastal areas and damage to shellfish beds as a result of bottom trawling meant that bait became scarce. Whilst legislation was passed to attempt to restore beds by preventing trawling, in reality little was done.

By the early 20th century, the large oyster beds of the Firth of Forth had declined beyond the point of return. The great line fisheries had also declined, and the majority of bottom-living fish were caught by the trawl. Many inshore areas could not withstand the high demand for fish and Scottish fishers had to travel to the northern North Sea and beyond as traditional fishing grounds became exhausted.

imageFigure 1 shows landings of bottom-living fish (i.e. cod, halibut, haddock) into Scotland from 1924 to 2007 taken from annual Scottish Sea Fisheries Statistical Tables. Landings declined during World War II but increased thereafter until the late 20th century, when they began to decline. However, landings alone do not show the whole picture as they may be influenced by a variety of factors other than the amount of fish in the sea. To gain a more accurate picture we need to take into account how technology has altered over time.

Figure 1. Landings of bottom-living fish by UK vessels into Scotland.
Source: Scottish Sea Fishery Statistical Tables.

clip_image005Figure 2 shows the fishing power of large Scottish trawlers. Fishing power is a measure of how fishers increase their catching ability over time e.g. technological improvements multiplied by the numbers of boats. Fishing power is measured in ‘smack units’, a smack being a typical 1880s sail trawler (see Thurstan et al. for full methodology). Figure 2 shows that overall fishing power increased rapidly throughout the 1960s, whilst landings only improved slightly during this period. Fishing power declined from the 1990s onwards as vessel numbers fell due to collapse in fisheries productivity and decommissioning.

Figure 2. Overall fishing power of large Scottish trawlers.
Source: Thurstan and Roberts, unpubl. data.

Figure 3 shows landings per unit of fishing power, that is, landings once technological innovations, vessel size, gear size etc. have been factored out. This shows the real situation much more clearly. Increased landings during the second half of the 20th century were in reality a result of technological improvements and more intensive fishing, which masked fish population declines.

clip_image007As we ran out of new places to fish we could not hide the problem of fisheries collapse any longer. Scottish bottom fisheries reached a peak around 1960, but then swiftly declined. These collapse in fisheries productivity occurred before the 200 nautical mile Exclusive Economic Zones were established and long before the Common Fisheries Policy began. Since then, vessel decommissioning schemes and conservation quotas have been insufficient to improve bottom fishery prospects (as yet there is no uptick in landings per unit power in Figure 3), despite the recent reduction in fishing power seen in Figure 2.

Figure 3. Landings per unit of fishing power.
Source: Thurstan and Roberts, unpubl. data.

A recent report to the Scottish Government showed that bottom-fish stocks are generally in a severely depleted state and that more needs to be done to conserve fish populations. Some stocks such as Nephrops are in better condition, ironically in part because of decline of their predators, such as cod and halibut. However, the widespread loss of bottom-living fish and shellfish such as oysters means that our seas are much less diverse and resilient than they were 150 years ago.

If we are to begin to reverse this trend, much more needs to be done. Destructive fishing activities need to be limited to allow habitats to recover and populations to bounce back. Groups such as SSACN are doing important work to understand shark populations through their Tagathon schemes, and to minimise impacts on fish populations through their Give Fish a Chance program. Other work in Scotland, such as the no-take zone at Arran on the west coast is also showing promising results for scallop populations (L. Howarth pers. comm.), whilst promoting the importance of allowing parts of our marine environment to recover from direct human impacts. There is definitely room for optimism, but we need to keep up the pressure on politicians and marine managers. It is important for everyone that we regain our once productive and diverse seas.

Ruth Thurstan is studying for a PhD at York University. Her research focuses on changes to UK marine ecosystems over the last two hundred years as a result of fishing activities. She hopes that this work will provide appropriate baselines by which suitable restoration and recovery targets can be set for UK seas.

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