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Crayfish Plague

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CASE NAME: European Crayfish Dispute


1. The Issue

On 18 May 1994, The European Court of Justice (ECJ) delivered case C-131/93 in which the European Commission sued the Federal Republic of Germany for initiating a ban on live crayfish imports. The ban of 1 August 1989 was a response to the fungal disease (Aphanomyces astaci) commonly known as the crayfish plague, spread mainly by the incorporation of alien species of crayfish. The German law required an import license to be obtained before live crayfish could be imported into Germany. Even with such a license, crayfish could be imported only for research and teaching purposes. This adversely affected eight to ten German firms engaged in the importation and distribution of live crayfish. A conditional exemption was, therefore, provided allowing the importation of crayfish for a limited time. The exemption required that the precise quantity, the country of origin and species name be specified. The Commission argued that such restrictions were in violation with the EC Treaty because it established import bans against member states. The ECJ agreed with the Commission and found the ban meant that Germany was not fulfilling its obligations of the EC treaty.

2. Description

The decapods called crayfish, otherwise known as crawfish or crawdads, are freshwater crustaceans (although a few species of crayfish live in brackish or salt water). They are closely related to and resemble the lobster and usually range in size from 3/4 of an inch to 16 inches. The average crayfish is usually 3 inches long, however some species found in Tasmania can be as large as 40 centimeters long and weigh up to 8 pounds. Crayfish are found in every continent except Africa and Antarctica and flourish in the temperate areas of the Americas and Eurasia. More than half or more of the 500 species are indigenous to North America. Crayfish are nocturnal and feed on all kinds of vegetation and animal food including snails, small fish, tadpoles, young insects and insect larvae and worms. Crayfish, however, are generally regarded as grazers and scavengers. Most crayfish live in lakes, ponds, reservoirs, rivers and streams where they often conceal themselves under rocks or logs. Others live in swampy places or wet meadows where they live in burrows. Some of the burrowing habits of crayfish have been known to destroy crop land or weaken levees and milldams.Crayfish are considered to be a delicious delicacy to both humans and other animals as they are often used as bait and are an important element in the diet of many animals such as the eel, trout, pike, chub, perch, otter and mink. In the United States, large numbers are raised on fish farms.

In many parts of the world, crayfish are consumed in large numbers by humans. In Europe consumption is high, therefore, it is not surprising that the spread and increasing severity of the crayfish plague (Aphanomyces astaci) has been of great concern to Europeans, as they have seen the numbers of native crayfish dwindling. Recent studies have shown that the crayfish plague is not indigenous to Europe, rather it was introduced by the incorporation of new species of crayfish from the Americas. The three species commonly imported to Europe from the Americas are Orconectes limosus, Pacifastacus leniusculus and Procambarus clarkii.

Orconectes limosus is indigenous to the great rivers of the interior basin of the United States specifically the Missouri, the Mississippi, and the Ohio rivers. However, it can also be found in the northern part of Texas to Canada and from Kansas to the Appalachian Mountains. (Hobbs, 1942, 153) Procambarus clarkii can be found in the southern United States from Texas to South Carolina with its origin in the southern part of Alabama and Georgia. (Hobbs, 1942, 99-100) Pacifastacus leniusculus is commonly known as the signal crayfish and is a native to the northwestern United States and Western Canada. This is an ideal crayfish for importation since it is larger than most European species and just as tasty. In addition, the signal crayfish is easy to culture, reaches sexual maturity earlier and grows quicker than European Crayfish.(Marren, 1986, 46)

Figure 1

No one is really sure how infected American crayfish were originally introduced to Europe. Some speculate that they entered by means of Italy from the release of ballast waters from a North American ship. Others claim that American crayfish, which are often carriers of the plague, were originally introduced as a food species. (Marren, 1986, 46) In actuality it does not matter how American crayfish or the crayfish plague were introduced into Europe. The fact is that once introduced, the deadly plague has spread rather quickly. After its original introduction c.1860 in Seligo Italy it ravaged north to both France and Germany and had been discovered in Sweden by 1907, Spain in 1958, Norway in 1971, Great Britain in 1981, Turkey in 1984, and Ireland by 1987. (Taugbol, 1993, 75)

It is thought that the plague is spread by both natural diffusion and by gradual movement over several generations. It has also spread by means of jump dispersal or movement over great distances. This often involves other animals transplanting the fungus. (Workshop:The Problem) An example would be anglers (fishermen) who use live crayfish as bait, (Reynolds, 1988, 283) feeding mink, raccoon, otter and migrating waterfowl also might transport the plague. The disease can also be spread without the actual introduction of an individual. The transfer of boats between lakes and the movement of hunters and fishermen are thought to transmit the fungus. Once the actual fungus is introduced into a waterway, it spreads quickly and without assistance. The natural movement of the water will transport the spores downstream and infected crayfish will move the disease upstream. Terrestrial animals, bathing, fishing and boating activities will also accelerate the diffusion of the plague. (Taugbol, 1991, 81)

The plague has all but eliminated many of the native European crayfish. Among the species in question belong to the genus Astacus and include Astacus leptodactylus, Astacus pachypus, Astacus torrentium, Astacus astacus and Austropotamobius pallipes. Astacus astacus and Austropotamobius pallipes are the most notable of these species. Austropotamobius pallipes is otherwise known as the white-clawed crayfish, and is the most common in Europe. Astacus astacus is commonly known as the noble crayfish and is the largest of the European freshwater species of crayfish. This is the species of crayfish most coveted in Europe as most Europeans consider it to be the most delicious of all the native species. (Marren, 1986, 46)

The crayfish plague is actually a fungus which is nutritionally dependent on these decapods. (Unestam, 1969, 4) It is difficult to identify until the actual death of the crayfish. Physical signs of the plague can be detected on the corpses of rotting individuals on the banks of waterways. The most notable of the physical signs of Aphanomyces astaci is woolly puffs of fungal threads which appear between the abdominal segments of the individual. There are, however, other less subtle ways of detecting an infestation of the plague.Perhaps the most obvious of such indications is a rapid and total extermination of crayfish stocks. Changes in behavior can also be observed. Infected crayfish, who are normally nocturnal, begin to wonder into broad daylight where they appear dazed, disoriented, and confused.(Marren, 1986, 46) Many of these staggering decapods leave the water altogether.Sadly, native European crayfish have not been able to develop resistant strains in spite of an enormous selection pressure. (Unestam, 1969, 4)

The plague has had serious implications to the ecology of European waterways. There is a real danger that native species of crayfish will disappear altogether. (Marren, 1986, 48) This has already happened in countries such as Sweden where entire native crayfish populations were totally eradicated within weeks or months after infestation. By 1969, it was estimated that 50% of the Swedish waters which were once home to native crayfish have lost their inhabitants due to this devastating plague. (Unestam, 1969, 4) Since crayfish are such an important part of the diet of mammals and fish such as the trout, pike, chub and perch, the fishing industry has suffered and lakes have become weedy and turbid. Overgrown waterways have disturbed the natural habit of fish, making them no longer suitable to sustain them. (Marren, 1986, 48)

People originally did not know what caused the crayfish plague, an obvious solution to the problem of the plague was to restock the native species with similar disease free crayfish from North America. These North American crayfish, particularly the signal crayfish appeared to have a high resistance to the plague. What was not known at the time was that these new inductees ware carriers of the fungus. They harbored the disease in a chronic or latent infection and functioned as a vector for the disease. (Taugbol, 1993, 81) Although Europe enjoyed short term benefits from these new crayfish including socioeconomic, commercial, recreational and biological value, many were unaware of the long term effects. Not only did the signal crayfish carry the disease, they posed other serious threats to the noble crayfish. The signal crayfish are more aggressive than the noble crayfish, which made itself apparent in competition and interbreeding which led to sterile hybrids. (Marren, 1986, 48) The signal crayfish also has a different susceptibility to predation than the native noble crayfish.

On August 1, 1989, The Federal Republic of Germany prohibited the importation of crayfish for commercial purposes. In particular, Germany prohibited crayfish importation for consumption or for release into private waters. They were concerned about water pollution but more concerned about the effects of the crayfish plague. Germany cited Paragraph 21b of the BUNDESNATURSCHUTZGESETZ (law on the Protection of Nature) which protected endangered species within Germany. Previously, Germany had imported tens of thousands of kilograms of live freshwater crayfish a year so the prohibition of crayfish importation had serious implications for international trade.

The European Commission stated that such a prohibition on the importation of crayfish was incompatible with Articles 30 and 36 of the EC treaty as it discriminates against member states. Article 30 of the EC treaty states that

Quantitative restrictions on imports and all measures having equivalent effect shall, without prejudice to the following provisions, be prohibited between Member States.(Rudden, 1996, 36-38)

Article 36 of the EC treaty states that

The provisions of Articles 30 to 34 shall not preclude prohibitions on imports, exports or goods in transit justified on grounds of public morality, public policy or public security; the protection of health and life of humans, animals or plants; the protection of national treasures possessing artistic, historic or archaeological value; or the protection of industrial and commercial property. Such prohibitions or restrictions shall not, however, constitute a means of arbitrary discrimination or a disguised restriction on trade between member states. (Rudden, 1996, 36-38)

The Commission did not deny the risk of plague or the need to protect native fauna. However they felt that the German law went further than necessary or appropriate to achieve these aims. In their view, the ban was an absolute ban on crayfish importation and therefore a ban solely for economic reasons. The Commission contended that the real aim of the ban was to protect German industry from competition within the European Union. They cited a similar French law which prohibited the importation of live crayfish only from non member countries. These laws might offer a non-discriminatory alternative in the form of licensing systems for the release of freshwater crayfish into the wild. In their view such a laws are more than appropriate since they aim to protect native fauna without discriminating against other member states of the European Union.

The European Court of Justice agreed with the Commission, saying that the Federal Republic of Germany failed to fulfill its obligation under ARTICLE 30 and ARTICLE 36 of the EC treaty, stating that their goals could have been achieved by measures with less restrictive effects. They found that health checks could have been imposed to ensure the health of imported crayfish. Such health checks would require the issuing of health certificates. Moreover, the Court found that measures could have been taken such as ones initiated in France. In short, they found that trade restrictions would not exclude the risk to transmission of the plague.

The introduction of non native crayfish into Europe has, thus, had dramatic effects. Not only have they introduced and spread a fatal fungus to the native population, they also have disrupted the host community, reduced biological diversity, disrupted the host environment and community, and provided a now permanent source of spores for plague fungus. This in turn has caused a reduction in fish stock and slower growth of local fisheries, changed the diet of indigenous mammals and has had negative commercial implications within Europe. One might conclude that all European countries should make it their goal to protect the native crayfish population. However, as case C-131/93 illustrates, import restrictions between members of the European Union is contrary to the EC treaty. Therefore, are no easy answers as to what to do about the crayfish problem within the European Union.

3. Related Cases

CAT case HOOF case
SHRIMP case SHRIMP2 case

Keyword Clusters

(1): Trade Product = CRAYFISH

(2): Bio-geography = TEMPERATE

(3): Measure = Regulatory Standard [REGSTD]

4. Draft Author: Christian S. Larson May 12, 1998



5. Discourse and Status: DISagree and COMPlete

There was originally a disagreement between the Commission and the Federal Republic of Germany concerning restrictions about the importation of live crayfish for commercial purposes. However, following the decision of case C-131/93 in 1994, there has been no further recourse. The decision stated that a law restricting intra-Community trade was contrary to ARTICLE 36 of the EC treaty. This article essentially states that a member state can not impose trade restrictions against another member state of the European Union.

6. Forum and Scope: EURCOM and REGION

The original decision was based on a national law within the Federal Republic of Germany. (Bundesnaturschutzgesetz) The Bundesnaturschutzgesetz is a general law with the goals of nature protection and landscape conservation. In particular, it aimed to maintain and develop (1) the efficiency of the ecosystem, (2)the utilization of natural resources, (3)the plant and animal world and the variety and beauty of the natural landscape. However, other non-German States within the EU protested against the regulation based on the Bundesnaturschutzgesetz, stating that it discriminated against non-German distributors of crayfish.

7. Decision Breadth: 15 (EURCOM)

This decision directly affected 15 member states of the European Union as the decision affirmed that trade restrictions could not be imposed against member states. However, with discussion of a possible enlargement of the European Union, other states may be affected in the future. Such states could, include Turkey, Cyprus, Malta, Switzerland, Hungary, Poland, Rumania, Slovakia, Latvia, Estonia, Lithuania, Bulgaria, the Czech Republic, and Slovenia.

8. Legal Standing: LAW

All decisions handed down by the European Court of Justice must be followed by all member states and supersede all national laws. The primary responsibilities of the European Court of Justice are to interpret treaties (such as the Treaty of Rome) and EU legislation which is often vague due to attempts at consensus building. In addition to adjudicating intra-community disputes, the ECJ has the task of ensuring that member states comply with all decisions. Community case law, of which case C-131/93 is an example, has proved to be a vehicle for advancing the objectives of the Treaty of Rome. (Dinan, 1994, 301) Among these objectives are the common external tariffs, a customs union and the free movement of goods, persons, services, and capital.



9. Geographic Locations

a. Geographic Domain : EUROPE

b. Geographic Site : Western Europe [WEUR]

c. Geographic Impact : GERMANY

Since Germany was the sole state being sued by the European Commission, it was the primary party affected. However, all states within the union are required to follow the decisions of the European Court of Justice. Thus, all states within the European Union are prohibited from restricting trade within the union.

10. Sub-National Factors: NO

German importers of crayfish are, once again, obliged to compete with all other importers of live crayfish from within the European Union. They can no longer enjoy the barriers to trade as established by the BUNDESNATURSCHUTZGESETZ even though the Germans contend that such trade might have negative effects to the local fauna within Germany.

11. Type of Habitat: TEMPERATE



12. Type of Measure: Import ban [IMBAN]

The Federal Republic of Germany placed a ban on the importation of crayfish in an effort to protect native species from a deadly fungus known as Aphanomyces astaci. The European Court of Justice, however, ruled that member states can not implement import bans against other member states. As a result Germany was forced to lift the ban. Precedents for such free movement of goods was made in 1979 when the court handed down its ruling in the now famous Cassis de dijon decision. This decision essentially allowed the Commission to develop the principle of mutual recognition. Mutual recognition is one of the most important elements behind the concept of a single market. Mutual recognition was defined as...

Any product imported from another member state must in principle be admitted ... if it has been lawfully produced, that is, conforms to rules and processes of manufacture that are customarily and traditionally accepted in the exporting country, and is marked in the territory of the latter.(Dinan, 1994, 117)
This is why states find it necessary to implement import bans only against non-member states. Such action is not contrary to the trade laws of the European Union since these import bans are only against states outside of the European Union.

13. Direct vs. Indirect Impacts: DIRect

The German law in question, the Bundesnaturschutzgesetz, provided the legal basis for the German government to directly ban the importation of live crayfish except for the purposes of research or teaching. The Bundesnaturschutzgesetz was implemented to protect the nature and landscape of Germany. In particular, it was enacted in an attempt to maintain a healthy and viable ecosystem. Such aspects of the ecosystem like the soil, water, air, climate,vegetation and animals were protected. This law is relevant to Germany's decision to ban the importation of live crayfish since it guarantees the protection of the habitat and living conditions of native species. The crayfish plague carried by foreign species of crayfish was seen as a threat to the habitat and living conditions of natural species of German crayfish. Since the import restriction was overturned by the European Court of Justice, no ban exists prohibiting the importation of live crayfish into Germany from member states of the European Union.

14. Relation of Measure to Environmental Impact

a. Directly Related : YES

b. Indirectly Related : NO

c. Not Related : NO

d. Process Related : YES

The ban against the importation of live crayfish was implemented in an attempt to protect local fauna. Since imported crayfish may carry the crayfish plague, they may spread the disease to native, non-infected, individuals.This in turn would adversely affect the local ecosystem. The loss of crayfish would disrupt the food chain in Germany, denying mammals and fish an important part of their diet. This could potentially lead to overgrown waterways and other environmental concerns. In order to prevent similar environmental hazards, the Commission published the Common Customs Code in 1992. The Common Customs Code required the establishment of border checks to insure that imported goods complied with a wide array of plant and animal health requirements. The purpose was to control the spread of disease. (Dinan, 1994, 336) In the spirit of the Common Customs Code, the ECJ found that instead of implementing an import ban, the Federal Republic of Germany could have required health checks. Such health checks would be accompanied by health certificates issued by competent authorities insuring that imported crayfish presented no health and environmental risks to native fauna..

15. Trade Product Identification: CRAYFISH

States within the European Union may implement import bans but not against other member states.

16. Economic Data

In 1986, crayfish retailed for a price of about $17.60 per kilogram. (Marren, 1986, 48)Since the maintenance cost of raising crayfish is relatively low and crayfish are consumed in great numbers throughout Europe, a large guaranteed market is present. The average noble crayfish is approximately 4.8 centimeters in length, therefore,the average crayfish might have retailed for about $7.39 per individual. This might seam to be quite expensive because a price of $7.39 reflects the price of imported individuals. Home-grown animals can be sold cheaper than imported crayfish. (Marren, 1986, 48) An examination of the estimated costs and returns of a crayfish farm in Louisiana in 1988 provides an example of just how inexpensive home grown specimens might be. Table 1 represents actual data from such a farm in Louisiana. The wholesale price of wild crayfish averaged $.50 per pound or $.46 for the same 4.8 centimeter long noble crayfish. Most crayfish are not this inexpensive as most crayfish sold on the market are not caught in the wild. Rather, most crayfish sold for consumption are raised on crayfish farms. These crayfish farms present the added cost of environmental controls, shipping, refrigeration, peeling, cooking, feeding and labor. Nether the less, domestic crayfish are cheaper than imported ones. It is for this reason why the Commission regarded the import ban to be in violation of ARTICLE 36 as enormous profits approaching $6.93 might be made on each individual retail crayfish sale made without intra-Community competition.

Table 1


MonthUnitPrice ($)QuantityAmount ($)
Jan lb.60200120.00
Feb lb.50300150.00
Mar lb.40300120.00
Total 800390.00

source (McMarius, 1988, 52)

Germany argued that this was not the case as their native populations of crayfish were dwindling due to both pollution and the plague. It is estimated that the plague has already wiped out as much as 50% of Sweden's crayfish waters. According to the German BUNDESNATURSCHUTZGESETZ, measures had to be taken to attempt to save the remaining native German crayfish population.Unfortunately, it is highly unlikely that further spread can be prevented at this time. Once the fungus is introduced into a waterway, its spread occurs almost instantly. In addition, the plague can be spread without the introduction of new individual crayfish. Waterfowl and boats being transported from lake to lake are thought to spread the fungus causing the crayfish plague. If one lake can produce 55.5 million adults at a profit of $6.93 per individual, the economic incentives to protect the native population is staggering ($384.6 million). Harvesting all of the adult crayfish from individual lakes,however, would lead to diminishing returns. As such, Germany argued that in the period from January 1989 to June of 1993, it issued special licenses allowing companies to import live crayfish for consumption. 961,400 kgs (2,119,887 pounds) were actually permitted into the country. At $17.60 per kg, this could have amounted to the importation of $3.7 million worth of live crayfish a year. The economic incentives behind the crayfish industry are thus, quite high.

17. Impact of Measure on Trade Competitiveness: HIGH

By charging that the German law unfairly restricted trade from other member states of the European Union, all member states of the EU may now import crayfish into Germany. However the decision of the European Court of Justice has broader implications as it affirmed that trade of any kind could not be restricted within the boarders of the European Union.

18. Industry Sector: FOOD

19. Exporter and Importer: EUROPEAN UNION and GERMANY



20. Environmental Problem Type: HABIT

It is feared that the crayfish plague is dangerous enough to cause the actual extinction to some of the five species of crayfish which are indigenous to Europe.Some of the native species of crayfish have already disappeared from areas in which they used to inhabit. In addition to the crayfish plague, crayfish are extremely sensitive to pollution and the over enrichment of waters from sewage and fertilizers. Crayfish need sufficiently clean and well-oxygenated and alkaline water. It is believed that both the plague and pollution have caused the native populations of crayfish to disappear from many streams and ponds.

21. Name, Type, and Diversity of Species

Name: Crayfish

Type: Crustacean

Diversity: 2 crayfish per square meter

IUCN Status VULNERable

It is difficult to estimate the diversity of crayfish since they are extremely sensitive to their environment. For example, crayfish can not breed in areas where the average water temperature in the summer months falls below 15 degrees Celsius even though adult individuals can survive under such conditions. Pollution and illumination are other factors affecting crayfish diversity. Despite this, a diversity of 2 crayfish per square meter is quite large. This means that a pond which is 25,000 square meters might be home to 50,000 individual crayfish. A lake the size of lake Tahoe in Sweden was once thought to be home to 55.5 million adult crayfish which would weigh approximately 1,110 metric tons. (Sture, 1971, 5-9)

22. Resource Impact and Effect: MEDium and REGULatory

The issue of the crayfish plague in Europe is a problem of resource depletion.If the crayfish plague is allowed to spread, the five species of crayfish native to Europe (Astacus astacus, Astacus leptodactylus, Astacus pachypus, Astacus torrentium and Austropotamobius pallipes) face extinction.

23. Urgency and Lifetime: MEDium and 1 to 20 years
(depending on species)

24. Substitutes: NONE

There is no real substitute for the crayfish however native species, such as the nobel crayfish, can be replaced by the signal crayfish or other disease resistant species from North America. The problem with such replacement would be the permanent loss of native European crayfish. In an attempt to increase the numbers and profitability of crayfish, however, people within the industry find it useful to resort to artificial crayfish ponds made possible by increases in technology in the 1960's. Such crayfish farms have made crayfish harvesting a year round industry in contrast to the catching of wild crayfish in the spring months. These farms find it possible to increase crayfish populations by means of artificial "seeding" and temperature controls. An unlimited demand for crayfish can now be filled as crayfish farming has become the mainstay of the crayfish industry, supplementing the natural wild supply. Unfortunately, crayfish farms are not immune to the plague as the plague can be spread without the introduction of actual individuals. Thus, raising a farm of European crayfish could be disastrous to the crayfish farmer as he could find his entire stock of crayfish wiped out weeks of, if he is lucky, months after infestation. Crayfish farms pose other potential environmental problems. It is very possible that individual crayfish might escape if they become unsatisfied with their environment. Chicken wire or other types of wire fences are often the only barriers between captive crayfish and freedom in the wild. Infestation within a farm could then theoretically be spread to the wild by means of wondering individuals. In addition, crayfish farms have to contend with problems of contaminated water. This might cause problems for both disposal and replacement.

F. OTHER Factors

25. Culture: NO

The crayfish plague has been a problem throughout Europe since it was introduced into Italy c.1860. Crayfish are used for the same purposes throughout Europe. Many states use crayfish for research and teaching purposes but, these factors play a relatively little role in the import ban implemented by Germany. The main use of crayfish is human consumption. Crayfish are enjoyed for this purpose throughout Europe. In this regard crayfish play a similar role in cultures throughout Europe. However, the conflict between Germany and the Commission was not a dispute concerning culture, rather it was a dispute over unfair trade practices.Germany had argued that in the period from January of 1989 to June of 1993, they had issued special licenses, allowing 961,400 kilograms (about 2,119,887 pounds) of live crayfish to be imported into the country. They contended that these licenses were not used to the full and thus, no crayfish were kept out of the country.The European Court of Justice, however, sided with the Commission. Germany was obliged to discontinue the import ban and to continue to import crayfish from all states within the European Union.

26. Human Rights: NO

27. Trans-Border: YES

28. Relevant Literature

Workshop:The Problem

Dinan, Desmond. Ever Closer Union : An Introduction to the European Community. Boulder : Lynne Rienner, 1994.

Esman, Marjorie R. The Town that Crawfish Built : A History of Henderson, Louisiana. Baton Rouge : Vaapr Inc, 1984.

Hobbs, Horton H. Jr., The Crayfishes of Florida, University of Florida Publication November 1942 Vol III no2.

Marren, Peter, "The Lethal Harvest of Crayfish Plague", The New Scientists v.109 p.46-50.

McManus, Brian E. and Tom Zacharias Projected Cost and Returns - Rice, Soybeans Corn, Milo, Wheat, Wheat-Soybean Double Crop, Rice-Crawfish Double Crop, and Selected Irrigation Enterprises - Southwest Louisiana Louisiana : Louisiana State University Agricultural Center, 1988.

Reports of Cases Before the Court of Justice and the Court of First Instance, 1994 "Free Movement of Goods: Commission v. Germany," nos 7-8 pt.1 pp I-3305-I-3324.

Reynolds, Julian, D., "Crayfish Extinctions and Crayfish Plague in Central Ireland", Biological Conservation 45, (1988), 279-285.

Rudden, Bernard and Wyatt, Derrick, Basic Community Laws sixth edition Oxford 1996 pp.36-38.

Sturs, Abrahamsson Population Ecology and Relation to Environmental Factors of Astacus Astacus Linne and Pacifastacus leniusculus Dana : Lund Department of Animal Ecology University of Lund, 1971.

Taugbol, Trond and Skurdal, Jostein, "Crayfish Plague and Management Strategies in Norway", Biological Conservation 63, (1993), 75-82.


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