II REVIEW OF REPLIES OF QUESTIONNAIRE - PART B. TROUT CULTURE

J. From - Danish Trout Culture Research Station (Skaerbaek, Denmark)

1. GENERAL INFORMATION

1.1 Total Area

The figure of 3 ha given for Ireland is open to question as the author knows of only one Irish trout farm whose ponds have an area of 2.2 ha.

1.2 Total Production

The production is mostly of rainbow trout (Salmo gairdneri), but the following species are also raised: sea trout (Salmo trutta trutta), brown trout (Salmo trutta fario), lake trout (Salmo trutta lacustris), Atlantic salmon (Salmo salar), char (Salvelinus alpinus), brook trout (Salvelinus fontinalis), Salvelinus (Cristivomer) namaycush, Coregonus peled (=C. muksun), Coregonus pidschian (kilch) and grayling (Thymallus thymallus).

1.3 Number of Trout Farms

Austria reported 30 big farms and several hundred small ones. Niedersachsen (Federal Republic of Germany) has 45 farms where fish culture is the principal occupation and 240 farms which rear fish as a sideline.

2. BIRD PROBLEMS

Most countries claim to have problems with birds. Normally these consist of predation, but involve spreading of diseases (see Table 4), and to a lesser extent interference with feeding (Belgium, Bayern (Federal Republic of Germany) and stress (Oulu Fish Farm (Finland)).

3. PROTECTION AGAINST BIRDS

All respondents, except for that of Niedersachsen, reported that nets or threads are the most effective measure. Their effectiveness depends on the distance between them and although no information was given for most countries, the maximum distance between threads allowed in Denmark is 20 cm.

Tripwires were mentioned by Austria, Niedersachsen and the United Kingdom. However, tripwires were judged to have no effect in the first two of these and the United Kingdom just mention that they are used.

Optical and acoustical signals were mentioned by Austria, Denmark, Inari fish farm (Finland), Oulu, Niedersachsen, Nordwürttemberg (Federal Republic of Germany), the Netherlands, Poland and the United Kingdom. Poland mentioned that shooting is sometimes used. Apart from Poland all reported that these measures are ineffective.

The Institute of Parasitology, Abo (Finland) mentions the use of scare crows and Nordrhein-Westfalen (Federal Republic of Germany) mentions dogs. Niedersachsen, which claims that threads have only limited effect, states that shooting of some grey herons (Ardea cinerea) proved to be very successful. Further, providing special feeding ponds for the birds has proved successful in some areas. Nordwürttemberg and the United Kingdom both advocate steepsided ponds with deep water as a protection against grey heron.

Table 4

Characteristics of trout farms in Europe and the degree to which they experience bird-related problems

It may be concluded that nets and threads are the only measures which give satisfactory protection against birds.

4. PREDATION

All the answers that mention grey heron (Ardea cinerea) put this species as the most important. Further, gulls (Larinae) are important predators, too. The following species were reported by the countries listed:

Answers to the questionnaire gave little indication as to the size of fish subject to predation. The only data available were reported as follows:

5. DISEASES

See Part D - Fish Diseases

6. LEGAL POSITION

See Part C - Bird Predator Populations (Legal Position)

7. RESEARCH

See Part C - Research.

8. ECONOMICAL IMPACT

The Netherlands is the only country where partial compensation for damage resulting from bird predation has been obtained from the Government. This was due to a special circumstance when a licence to shoot birds was not granted in time. Estimates of economic impact for some countries are as follows: