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Resources and depletion

The North Sea and its coasts are a vast natural resource, used intensively and in a great variety of ways by the surrounding coastal states and the international community. The heterogeneous nature of the North Sea - its marshes, estuaries, and open waters - provides a wide range of habitats that support a varied and abundant wildlife. This ranges from the smallest unicellular organism to fish, large colonies of seabirds, and mammals (such as seals and dolphins). Several coastal areas that are of exceptional scientific and environmental interest have been designated as nature reserves. The most important is the Waddensea, lying to the north of the Netherlands and abutting the German and Danish coasts. This area is world renowned for its biological productivity, offering habitats for over half the European populations of waders, ducks, and geese (van der Zwiep 1990). This area also contains 21 per cent of all remaining North Sea salt marsh, and provides the nursery for 80 per cent of all plaice and 50 per cent of all sole caught in the North Sea.

Much of the coastline is used for enjoyment and relaxation by the urban population as well as by local communities. The North Sea is one of the most productive fisheries in the world and certain types of the bottom strata are an important source of sand and gravel for the aggregate industry. The Straits of Dover and the southern North Sea are among the most heavily trafficked sea routes on the globe, serviced by large commercial ports and smaller, local ports and harbours dotted along the coasts. The oil and gas fields situated in the central and northern North Sea are a major economic resource. At the same time, the North Sea receives much of the domestic and industrial effluent from the countries surrounding it.

Before the present century, human activity in the North Sea was on such a scale that it had little widespread impact on these resources and no one activity interfered very much with any other. With increased population, growth in industrial activity, and vastly expanded technical capabilities of states using the North Sea, it is becoming increasingly clear that resources, even those that are considered renewable (such as fish stocks), are near the point of overexploitation and in management terms many are in conflict with one another.

Marine ecology of the North Sea


Considerable marine biological productivity emerges from the high input of plankton nutrients spilling in from the north-east Atlantic and some additional nutrients from rivers that discharge into the North Sea. Open waters in the northern North Sea are stratified, for the most part, from late spring to autumn so that vernal and autumnal outbursts of phytoplankton utilize nutrients. These blooms can occur at the fronts that exist between water masses with different characteristics. These phytoplankton populations undergo annual "ploughing," which recycles nutrients in the water column. In addition, because the sea is shallow it has a rich benthic fauna sustained by detritus, and this forms a food supply for fish (Lee 1988).

All the following figures are from De Wolf and Zijlstra (1988). Van den Hoek and colleagues (1979) estimated that there are over 500 species of phytoplankton in the Waddensea alone, though there are undoubtedly more for the North Sea as a whole. The phytoplankton populations in the North Sea are studied in two ways:

1. through the Continuous Plankton Recorder Survey (CPRS), which has recorded spatial and temporal occurrence and variation since 1958 (Grover 1967; Glover, Robinson, and Colebrook 1974); and

2. through the study of phytoplankton dynamics in relation to nutrients, availability of light, hydrographic properties (e.g. salinity, temperature and mixing, grazing of zooplankton).

Data from the continuous survey between 1958 and 1973 indicate significant long-term changes (Reid 1978; Reid and Budd 1979). These changes are thought to relate to the position of the Gulf stream and to climatic change (Garrod and Colebrook 1978; Radach 1982; Reid and Budd 1979). Changes in the phytoplankton were accompanied by a general decline in zooplankton.

The data available for zooplankton are similar to those for phytoplankton, the major data source being the CPRS. Species caught by the CPRS are listed in table 8.2. These species have been regularly observed by the CPRS and only a few appear to be dominant, with the total number of species estimated at less than 300. Variations in their distribution prevail throughout the southern, central, and northern regions of the North Sea.

Table 8.2 Zooplankton in the North Sea

Species No.
Branchiopoda (s) 5
Calanoid copepods (s) 22
Cyclopoid copepods (g) 3
Malacostraca (f) 7
Planktonic Gastropods (s) 4
Tunicates (s) 4
Chaetognatha (s) "few"
Polychaete Tomopteris (g) 1

Source: De Wolf and Zijlstra (1988,130-131).
(s) = species
(g) = genera
(f) = family

Table 8.3 Numbers of species in infauna and epifaunal macrobenthos.

Area Polychaetes Molluscs Crustaceans Echinoderms
German Bight (1985) 90 54 52 12
German Bight (1978) 68 38 55 9
Central North Sea - - - 57
Doggerbank 143 - - -
Oyster Ground - 63 - -
West of Scheveningen 62 16 49 5
57°20'-54°40'N and 2°20'-5° E 2 75 56 20

Source: De Wolf and Zijlstra (1988,134).


The zoobenthic organisms are usually divided into three categories of micro-, meso-, and macrobenthos. Table 8.3 shows the number of species of infauna and epifaunal macrobenthos.

Table 8.4 Data on 11 important fish species in the North Sea fisheries

Species Average landing 1965-1969 ('000 tonnes, fresh weight) % of total landings Industrial catch 1974 ('000 tonnes) Habitat Distribution
Herring 933 30.7 88 Pelagic All North Sea
Mackerel 618 20.4 230 Pelagic All North Sea
Haddock 287 9.5 44 Demersal North, central
Cod 227 7.5 5 Demersal All North Sea
Norway pout 179 5.9 753 Pelagic North, central
Sandeel 157 5.2 512 Pelagic Central, south
Whiting 139 4.6 117 Demersal All North Sea
Plaice 106 3.5   Demersal Central, south
Coalfish 86 2.8   Demersal North
Sprat 77 2.5 243 Pelagic All North Sea
Sole 25 0.8   Demersal Central, south
Total 3,036 100.0      

Source: Adapted from De Wolf and Zijlstra (1988, 137).


The greatest amount of information available on North Sea organisms has been collected on the commercial fish stock. Because of the very intensive fishing of the North Sea, most fish species occur either as the catch or as the by-catch (Tiews 1978). This fishing effort has considerably changed the ecosystem, however, and fisheries are adapting rapidly to these changes.

It is estimated that there are approximately 160-170 fish species in the North Sea (Wheeler 1969, 1978). Although values can vary from sample to sample, it can be concluded that around 25-30 species are very common (table 8.4).

A more detailed explanation of the fishing industry in the North Sea is given later in this chapter.


Bird populations fall into two groups - coastal and open sea. The littoral populations breed along the coasts, collecting food from the open sea, intertidal mudflats, and inland areas. They usually migrate over the sea at the end of the breeding season. The open-sea birds breed along the coasts, collecting food from the open sea. They normally stay in open sea for six months during winter.

Bellamy and colleagues (1973) list 71 species of coastal and open-sea birds along and on the North Sea. According to Camphysen and van Dijk (1983) many more species live along the coast of the Netherlands. However, only limited data are available on the number of open-sea bird species present in the North Sea, although Evans (1973) lists 19 such species, with a winter population of 21 species.


Seals usually occur along or near the coast, spending part of their time on land or on dry tidal flats in the breeding season and the rest of their time in the water. There is a wider knowledge of seals than of cetaceans as they are easier to study. There are six species in the North Sea, of which four are rare or occasional stragglers and two are common (and are discussed here).

Grey seals are mainly found in the west and north-west of the North Sea and are only occasionally located in the eastern regions. Their population in the United Kingdom is thought to be around 29,000-32,000 individuals (Summers, Bonner, and van Haaften 1978). The grey seal used to be common in the German Bight.

The common or harbour seal, as it is sometimes known, lives seaward of the German Bight, the Wash, and the English and Scottish east coast, with estimated populations of around 4,500-5,000, 6,000, and 7,000-10,000, respectively (De Wolf and Zijlstra 1988, 140).

A report from the Food and Agriculture Organization (FAO) of the United Nations in 1978 noted that, over the whole extended range, the seal population seems to be stable. However, there are clear indications that the common seal suffers from the effects of polychlorinated biphenyls (PCBs).

The total food consumption of the seal population in the North Sea is estimated at around 100,000 tonnes per annum, with the common seal requiring 5 kg of fish per day and the grey seal consuming 5-8 kg per day. The favourite fish species of the seals are cod and salmon.

There are known to be 30 species of whales and dolphins in the North Sea: 22 are rare or occasional stragglers, known only because of strandings, whereas 8 occur regularly and in large numbers. These are all dolphins. Whales are extremely rare in the North Sea.

There are two dolphin species with a tendency for coastal distribution that are again better known about because of strandings. These are the harbour porpoise and the bottlenose dolphin (Verweij and Wolff 1982).

Less common species such as the common dolphin, the white-beaked dolphin, the white-sided dolphin, and, in the north, the beluga and pilot whale are hardly known. In the period before the 1960s the minke whale was frequently observed, but there has been a severe decline due to whaling (Zijlstra 1988).

There has been a reduction in population owing to pollution or a reduction in prey, which is thought to be causal in the decline (Andersen 1984). The population is also declining owing to the accidental catching by faster and more powerful fishing vessels (FAO 1978).

Depletion of fish stocks

Fishing is the most established and extensive resource use of the North Sea, yet overfishing is one of the most critical resource issues facing the region today.

Roman merchants in Utrecht conducted active fishing businesses. Small fishing operations, which required relatively little capital outlay, flourished along the east coast of Britain. There are various records of herring fisheries from medieval times. The fourteenth century saw the first conflict between the British and Europeans over territorial fishing rights (Coull 1988). The Dutch were very skilled as a fisherries nation but were unable to meet the demand of the growing European market for fish.

The Dutch were the first to establish a substantial open-sea fishery for herring, and by the fifteenth century had pioneered the basic techniques of catching herring in drift-nets and curing them with salt in barrels, the dominant methods for herring fisheries until World War II. Extensive trading of the barrels, especially in the hinterland of the southern Baltic, provided a source of great wealth to the Dutch.

Up to the nineteenth century the British fishing industry had never been very strong and had declined to a point of danger that the country would lack trained soldiers and sailors to staff ships in times of war. In 1549, Fridays, Saturdays, and Lent were made "fish" days, and in 1563 Wednesdays were added. Although this gave temporary benefit to the industry, food regulations were never popular and were eventually abandoned.

The emergence of the fishing smack in 1830 transformed the British industry, which had previously relied upon the use of hook-and-gill nets (Morley 1968). By the mid-1800s the industry rapidly began to acquire a modern image, mainly because of improvements in fishing techniques and the spread of railways linking ports to large population centres. This shows up in the history of Grimsby town, which grew famous for its fishing trade (table 8.5). The railway allowed the transport of Norwegian ice from the port on the Humber to Grimsby, thereby boosting both the fish and lobster trade.

Table 8.5 Fish landings in Grimsby, 1854-1958

Year Amount of fish landed (tons)
1854 453
1856 1,500
1890 70,000
1900 135,000
1909 175,000
1958 220,000

Source: Adapted from Morley (1968,123).

The improved quality of fish reaching the consumer - owing to packaging ice as well as the opportunity for further transportation led to an unprecedented rise in the demand for fish. This demand in turn necessitated a drastic reorganization of the fishing industry.

By 1900 the British Isles had become the leading fisheries nation of the world at a time when the North Sea was positively abundant with all types of fish species. It has been estimated that British fishing boats caught approximately two-thirds of all herring and nearly all pelagic fish (Morley 1968). During World War I, however, fishing declined dramatically. After the war, the British fishing industry picked up again but never reached its prominent pre-war level.

The inter-war years saw increasing competition from the Germans, whose fish catches after 1925 nearly equalled the British catch. The Germans also competed for the export market and introduced significant changes in fishing methods (e.g. the use of drift-nets with trawlers instead of drifters). World War II again curtailed the fishing industry, but a post-war world shortage of animal oils and the increased use of fish-meal in foodstuffs prompted a change in the fish species sought. These species are known as industrial species (for example, the Norway pout) and included the trawling of areas in search of adolescent 23-year-old herring. The change in demand led to a reduction in the overall British catch, because Britain did not find it economical to engage in industrial fishing.

The current deep-sea-fishing challenge has been met by investment in new high-powered diesel craft and technology in navigation, in methods of locating fish shoals, and in equipment for freezing and processing on board.

Countries of eastern Europe and the former USSR expanded their distant-water fisheries, putting further pressure on the fish resources and increasing the total catches of North Sea herring.

The advent of the revolutionary purse-net in the mid-1960s raised the catching effort to an unprecedented peak. An increase in the strength of the synthetic fibres and the introduction of the power-block meant that purse-nets could now be used in the open sea, not just in sheltered waters to which they had initially been confined. The 1960s also saw the collapse of the surface herring fishery, mainly owing to new technology that enabled the identification of such shoals (MacGarvin 1990). The Norwegians changed fishing grounds from the North Atlantic to the North Sea.

The year 1972 saw the enlargement of the EEC to include two major fisheries nations, the United Kingdom and Denmark, which became influential in the formation of the Common Fisheries Policy (CFP). Norway did not join. In the 1970s there was a worldwide extension of Exclusive Economic Zones (EEZs) to 200 nautical miles, and in 1977 a median line was drawn between the EEC and the Norwegian EEZ.

In pelagic rather than demersal fisheries the diagnosis of overfishing is generally more problematic, and so effective remedies are difficult to formulate. Adult herrings tend to form different shoals from juveniles, which gives greater scope for mesh size controls. Conservation of shoals can be promoted by limiting the length of permissible fishing season or by complete closure. The herring also lays eggs on the seabed rather than letting them drift, a practice that allows ready identification of spawning grounds.

As the capacity and efficiency of fishing fleets increased over the years, concern grew regarding the impact on fisheries and their profits. The monitoring of catches began in the 1950s and was based on the monitoring of fish larvae and the prediction of the amount that would survive to adulthood. It was found that the adult population varied annually, owing to such factors as food availability, the prevalence of disease, and the effect of storms and currents. These unpredictable external factors have led to inaccurate mathematical modelling, which ironically has been used in the setting of fishing quotas. Short-term models have also been used to predict fish stocks but have been too short-sighted to provide an accurate picture of the capability of the stock to regenerate sufficiently (MacGarvin 1990).

Table 8.6 Recommended and adopted total allowable catches (TACs) and total catches for herring in the North Sea, 1974-1976 and 1982-1986 ('000 tonnes)

  1974 1975 1976    
Whole North Sea:
Recommended 310-356 136 0    
Adopted 305 183 160    
Catch 331 365 183    
  1982 1983 1984 1985 1986
Skaggerak & Kattegat:
Recommended 30-40 30 40 30-40 60-80 50
Adopted 61 59 - 117 46
Catch 147 198 205 n.a n.a.
South North Sea & East Channel:
Recommended 60 36 49 62 37-42
Adopted 72 73 49 90 70
Catch 69 64 46 n.a. n.a.
North and central North Sea:
Recommended 0 62 95 166 235
Adopted 0 72 -a 230 500
Catch 167 244 272 n.a. n.a.

Source: Coull (1988).
n.a. No agreement.

With overfishing a reality and spawning stock considerably reduced, it was imperative to impose catch restrictions. The principle of total allowable catches (TAC) was accepted from 1974, though effective conservation methods were slow to come into action. The United Kingdom used emergency powers of veto to prohibit all herring fisheries beyond its own 12 mile limit after 1977. This was eventually accepted by all countries in 1982. The resultant recovery of the stock has been claimed as one of the few examples of definite and positive results from the new management regime (Coull 1988). Despite the adoption of the principle of TAC, administrators, in the face of pressure from fishing interests, betray a strong tendency to raise the scientifically based advised levels (table 8.6).

It was agreed in 1983 that scientific models should be used to set target catches (i.e. TACs for each species of fish). This required a detailed knowledge of individual life cycles, and, in doubtful cases, species received a "precautionary" TAC (MacGarvin 1990). Not enough is known, however, to define the maximum possible catch consistent with survival.

As table 8.6 shows, economic issues can undermine the TAC principle, as can political pressure. Biologists now recommend that existing TACs should be halved in order to allow for some degree of regeneration (Symes 1990). For example, it is now estimated that over 55 per cent of the total stock (including recruitment age classes) is now caught annually.

TACs and overfishing have again become an important issue of political discussion. The Council of Fisheries Ministers of the European Communities met in 1990 to set annual catch limits and to discuss the preservation of fish stocks and the associated industry. The Council acted on scientific evidence that concluded that an overfishing of more than 90 per cent of fish stocks prevailed in the North Sea. The depletion of cod and haddock, in particular, was considered critical (Financial Times 1990a). The Council proposals, which were about half as restrictive as scientists wanted, included reducing the annual cod quota from 98,270 to 85,700 tonnes and the haddock quota from 41,700 to 40,500 tonnes. The Council also ruled that fishing boats near concentrations of cod should remain in port for 10 consecutive days per month, that net mesh sizes should be increased from 90 mm to 120 mm, and that net meshes should be changed from a diamond shape to a square shape.

Although the European Communities reached an unexpected agreement on the reduction of quotas, they did not agree on all conservation measures, in particular net mesh size. Furthermore, coastal states have not yet agreed on planned reductions in boat sizes for the 1990s (Symes 1990).

The total allowable catch for cod was pushed above the EC recommendations, to 93,570 (and not 85,700) tonnes, but it was down on 1990's TAC figure of 98,270 tonnes. The TAC for haddock was set at around 40,500 tonnes. Only "structural conservation measures" were agreed upon - boats near cod stocks were to be kept in port for 8 consecutive days, not 10, per month, and "generous EC funding" was envisioned to encourage the decommissioning of vessels to reduce overcapacity (Financial Times 1990b).

The North Sea foodfish decline is serious but not yet critical. The industry is steadily contracting, with much hardship to traditional coastal fishing communities. The politicians are caught in their own trap: TACs are too high and fluctuate annually, as described above. This is no basis for any long-term, controlled reduction in the fishing industry. Furthermore, the reduction in boat numbers is too small, because each quota chosen is politically embarrassing. One solution would be to allocate fishing quotas to the highest bidders, set within TACs. But this would result in a massive shakedown of marginal boats and skippers and is politically unthinkable at present. On balance, the North Sea foodfish industry looks set to remain above the pain threshold for many years to come.

Land reclamation

Land reclamation is a natural process. It usually takes place in sheltered areas such as estuaries, where rich alluvial deposit processes cause gradual accretion. The deposits eventually become colonized by plant species that drain the soil in a process known as soil ripening. The resulting soil can be drained further and is excellent for agricultural purposes, providing a stable, fertile soil for some years.

Gradually man came to the assistance of nature in the North Sea area to speed up the process of accretion. Salt-marshes were embanked to protect them from further inundation. This was the beginning of the operations of land reclamation, started by the demand for fertile farmland and a need for coastal protection, for new space for industry and commerce, and in some cases for building other structures such as roads or railways. Land reclamation in the United Kingdom dates back as far as the eleventh and twelfth centuries. Some areas of the Thames may have been reclaimed by the Romans, with other similar early works around the rivers in Kent and within the Humber estuary. One area that has been well studied is the Wash, where reclamation has been taking place since the Middle Ages. The first significant gain of land reported in this area was in the seventeenth century when around 15,400 ha of salt-marsh were embanked. By 1979 this had reached 31,000 ha.

Land-reclamation works have taken place in many areas along the North Sea coasts of Great Britain and the Continent - for example, at the Firth of Forth, on the banks of the rivers Tees and Humber, on the salt-marshes of the Wash, and in the Wadden area stretching from the city of Den Helder in the Netherlands to Esbjerg in Denmark.

The previously jagged coastline of the Wadden area has been either straightened or shortened artificially, resulting in the loss of tens of thousands of acres of land (including mudflats, salt-marshes, and summer polders) outside the dikes. Only an area of 375 kmē is left, representing less than 4 per cent of the Wadden area. And even these few areas are threatened by further reclamation.

Mineral extraction

Minerals required by construction industries originate from the ice ages of the Quaternary period. They are extracted on a national basis, as are oil and gas. (All figures are from Sibthorp 1975.)

With regard to the geological environment of the North Sea, only three groups of minerals are likely to be present in quantities sufficient to allow them to be economically worked. These are superficial, unconsolidated deposits, such as sand and gravel and the so-called "heavy minerals" (notably including sources of titanium); bedded deposits such as coal and evaporites (e.g. halite [salt], potash, and anhydrite); and petroleum and natural gas.

The only mineral being extracted on a large scale from sea water is magnesium. Extraction plants are located mainly at Hartlepool in the United Kingdom and in Norway. Current production figures are not available, although it is known that, earlier, 60-65 per cent of world magnesium production (1973 figures) was from sea water. Salt is also being recovered on a small scale at Maldon, Essex (UK).

Difficulty in obtaining sufficient building aggregate on land has led to the increased usage of marine aggregates since the early 1960s. By 1972 this was contributing around 12 per cent of total production in Great Britain. The most suitable deposits are located in the British sector of the North Sea, 7-20 miles offshore at various sites from the Humber to the Thames. The continental side of the North Sea is mainly sandy, with exceptionally rare gravel deposits. As a result, dredged aggregate is delivered from the British areas to Rotterdam, Dordecht, Bruges, Dunkirk, and Calais.

In 1972, about 6 million tonnes of sand and gravel were dredged from the North Sea. Technological developments and the building of very large dredgers now enable areas of lower-grade materials to be worked, but it is becoming clear that many reserves have become exhausted. Strata containing salt, anhydrite (calcium sulphate), and potash extend beneath the North Sea off the Yorkshire and Durham coasts. Salt is extracted near the Tees estuary by controlled pumping of a saturated brine solution through a network of boreholes. Although enormous deposits of salt have been found beneath the North Sea during the search for hydrocarbons, the existence of very large reserves of salt on land in Britain renders it unlikely that salt will ever be extracted from beneath the sea on a large commercial basis.

Potash occurs in an extensive bed at a depth of around 1,000 m over a very large area in Yorkshire, stretching from the Durham border to Scarborough and for a very considerable distance out to sea. Only a small proportion of this area is currently mined because of technical difficulties involved in extraction.

Several coalmines extend beneath the North Sea off the Northumberland and Durham coasts. Usable deposits are located mainly in the southern North sea and are extracted mainly by the United Kingdom, Denmark, the Netherlands, and Belgium. Most of the extraction takes place near the coast, on land, though the United Kingdom disposes of the wastes at sea. The United Kingdom is currently the only country that does this, on the grounds that it is inert material. It is likely that this practice will have to cease by the end of the century if not before (see below on industrial waste).

Oil and gas extraction

The first discovery of natural gas occurred in 1959 and production began in 1967. Since then large-scale production and exploration have been extensive. The search is continuing, with many of the main fields (e.g. the large Stratfjord field) already having been discovered. Gas is a non-renewable resource but it is a very important financial benefit to the economies of the countries (i.e. the Netherlands, the United Kingdom, and Norway) that have jurisdiction of the continental shelf.

Gas fields owned by the United Kingdom are situated mainly in the southern and central North Sea basin, located to the east of Yorkshire, Lincolnshire, and Norfolk. Some of the natural gas fields situated in the northern sector of the North Sea are not extensively exploited commercially. These were formed from the carbonization of flora and fauna in the Carboniferous period, the salt seal that formed above them preventing anaerobic decomposition. They are mostly owned by the Netherlands and the United Kingdom.

Oil fields are found mainly in the northern North Sea, from Jurassic shales. They are predominantly owned by the United Kingdom and Norway. North Sea crude oil is high quality, low in sulphur, and "light," and therefore suitable for the production of petrol and diesel fuel (but unsuitable for heating fuel). Considerable quantities of the mineral have been found in the northern North Sea off the Scottish coast.

The oil and gas reserves are of enormous strategic importance to the North Sea states. They contribute significantly to the wealth of the Norwegian economy and account for more than 10 per cent of the real wealth of the British and Dutch economic output.

With respect to oil, the best estimate for UK reserves is that North Sea oil will begin to decline in annual output around A.D. 2000-2010 and that the effective resource will be viable until around 2040 (BP 1991; UK Digest of Energy Statistics 1991-). Much depends on price and technological innovation. Certainly the scope exists for extending existing reserves, given the appropriate incentives.

For gas, the picture is similar to the UK oil reserves, with around 4050 years of availability at current rates of exploitation (BP 1991). Again, this could be expanded with suitable pricing and regulatory actions. For the Dutch and Norwegian reserves, the expected commercial lifetime is a little longer (about 50-60 years), bearing in mind a growing demand over this time for exports to other North Sea basin states (Kemp 1990).

The oil and gas industries are privately owned in the United Kingdom, and quasi-private in Denmark, Norway, and the Netherlands. Regulatory offices and tax and depletion policies strictly enforce controls over economic exploration. The international price for fossil fuels and the current preference for gas over new coal and oil on the grounds of thermal efficiency, lower carbon-dioxide generation, and lower sulphur-dioxide production influence the management of these resources. Co-generation of gas with oil is likely to increase as a consequence.

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