J. From - Danish Trout Culture Research Station (Skaerbaek, Denmark)
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.
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)).
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
Country | Area in ha | No. of trout farms | Product. in tons | Product. t/ha | Bird problems | Protect. against birds | Diseases | Research | |
Austria | Unknown | 2 500 | yes | yes | yes, no importance | no | |||
Belgium | 500 | 15 | 400 | 0.8 | yes | yes | yes | ||
Cyprus | 0.3 | 5 | 55 | no | no | ||||
Czechoslovakia | small | yes | yes | no | |||||
Denmark | 400 | 520 | 23 000 | 57.5 | yes | yes | yes | yes | |
Finland | |||||||||
Inst. of Parasitology, Abo | yes | yes | |||||||
Nat. Vet. Inst., Helsinki | yes | yes | |||||||
Inari Fish Farm | 0.2 | 9.0 | 45.0 | yes | yes | yes | no | ||
Montta Fish Breeding Station | 2.2 | 19.0 | 8.6 | yes | yes | yes | |||
Oulu Fish Farm | 1.1 | yes | yes | yes | no | ||||
France | 710 | 20 000 | yes | yes | no | yes | |||
Germany (Fed. Rep.) | 567 | 1 930 | 5 300 | 9.3 | yes | yes | locally | yes | |
Hungary | 3 | 300 | no | yes | |||||
Ireland | 3.0 | 19 | 560 | 186.7 | yes | yes | no evidence | ||
Israel | Unknown | ||||||||
Italy | yes | ||||||||
The Netherlands | 6.0 | 16 | 200 | 33.3 | yes | yes | yes | no | |
Poland | 2 000 | yes | yes | yes | no | ||||
Romania | 20.2 | 55 | 230 | 11.4 | no | no | no | no | |
Switzerland | 60 | 700–1 000 | yes | unknown | yes | ||||
United Kingdom | Unknown | 450 | 10 000 | yes | yes | probably | yes |
It may be concluded that nets and threads are the only measures which give satisfactory protection against birds.
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:
Grey heron (Ardea cinerea) | Austria Belgium Denmark Cyprus France Ireland Netherlands Switzerland United Kingdom | Federal Republic of Germany: Baden-Württemberg Bayern Niedersachsen Nordrhein-Westfalen Nordwürttemberg |
Gulls (Larinae) | Belgium Czechoslovakia Denmark Poland | Finland: Institute of Parasitology, Abo Montta Fish Breeding |
Federal Republic of Germany: Bayern and Niedersachsen | ||
Black-headed gull (Larus ridibundus) | Austria France Netherlands United Kingdom | Finland: Inari Fish Farm Oulu Fish Farm |
Federal Republic of Germany: Baden-Württemberg Nordwürttemberg Schleswig-Holstein | ||
Comm gull (Larus canus) | Finland: Inari Fish Farm Oulu Fish Farm | Federal Republic of Germany: Schleswig-Holstein |
Herring gull (Larus argentatus) | United Kingdom | Finland: Inari Fish Farm Oulu Fish Farm |
Great black-headed gull | Finland: Inari Fish Farm | |
(Larus marinus) | ||
Lesser black-headed gull | United Kingdom | |
(Larus fuscus) | ||
Kingfisher (Alcedo atthis) | Austria Belgium Cyprus Denmark France Ireland Poland (few) United Kingdom (probably) | Federal Republic of Germany: Baden-Württemberg Niedersachsen Nordrhein-Westfalen Schleswig-Holstein |
Cormorant | France Ireland United Kingdom | Federal Republic of Germany: Bayern |
(Phalacrocorax carbo) | ||
Great crested grebe | Poland | Federal Republic of Germany: Bayern Niedersachsen |
(Podiceps cristatus) | ||
Terns (Sterninae) | Denmark | Poland |
Arctic tern (Sterna paradisaea) | Finland: Inari Fish Farm | |
Common tern (Sterna hirundo) | Federal Republic of Germany: Schleswig-Holstein | |
Goosander (Mergus merganser) | Finland: Inari Fish Farm | Federal Republic of Germany: Bayern |
Hooded crow | Denmark | |
(Corvus corone cornix) | ||
Carrion-crow | Federal Republic of Germany: Nordrhein-Westfalen | |
(Corvus corone corone) | ||
Wild ducks (Anatidae) | Federal Republic of Germany: Bayern |
Answers to the questionnaire gave little indication as to the size of fish subject to predation. The only data available were reported as follows:
Austria | Predation takes place up to 15 cm | |
Denmark | Up to 500 g | |
Finland: Inari Fishfarm | Fish up to two years old, but bigger fish are wounded | |
Federal Republic of Germany: | ||
Bayern | All fish sizes | |
Niedersachsen | Grey herons eat fish 10–16 cm | |
Ireland | Fingerlings (6–30 g) are eaten | |
The Netherlands | Up to 200 g (marketable size) | |
Poland | 1–100 g fish are eaten | |
United Kingdom | Grey herons eat fish of 75 g. Cormorant takes fish on less than 1 kg. Black-headed gull, herring gull and great black-headed gull eat fish up to 10 cm |
See Part D - Fish Diseases
See Part C - Bird Predator Populations (Legal Position)
Austria | All birds are generally protected. Grey heron can be shot in lower Austria in September. In upper Austria gulls are only protected from 15 April to 15 July. |
Belgium | Grey heron and kingfisher are protected |
Cyprus | All fish-eating birds are protected |
Czechoslovakia | All fish-eating birds are protected |
Denmark | Grey heron is protected, but can be hunted all year round inside fish farms. Black-headed gull, common gull and herring gull can be hunted from 1 September to 29 February. Other gulls, terns and kingfishers are protected unconditionally. Carrion-crow and hooded-crow are protected, but can be hunted from 1 July to 30 April inside fish farms. No licence is needed to hunt birds on fish farms. |
Finland | Black-headed gull and herring gull are not protected. The other birds are protected, but all birds can be shot on fish farms if they cause damage. |
Federal Republic of Germany | Baden-Württemberg: Grey heron and kingfishers are protected. Black-headed gull can be shot. |
Bayern: Grey heron is protected from 16 September to 31 October. | |
Niedersachsen: All birds are protected all year, except for gulls which are protected from 30 April to 16 July and coot which are protected from 15 January to 1 September. Licence can be given to shoot the following birds on fish farms: gulls, grey heron, great crested grebe and coot. | |
Nordrhein-Westfalen: Kingfisher is protected. | |
Nordwürttemberg (Regierungsbezirk Stuttgart): Grey heron is protected. Black-headed gull is protected from 1 May to 15 July. | |
Schleswig-Holstein: Grey heron is protected, but licence can be given to shoot a maximum of 8 specimens/year within 200 m of the farm. Common tern, kingfisher and osprey are protected. Black-headed gull can be hunted from 16 July to 30 april and common gull can be hunted from 16 August to 30 April. | |
France | All fish-eating birds are protected. |
Ireland | Fish-eating birds are protected, but may be shot under licence if create damage. |
Italy | All fish-eating birds are protected. |
Poland | All fish-eating birds are protected. |
Netherlands | Fish-eating birds are protected, but may be shot under licence if create damage. |
Romania | No licences at fish farms can be given. |
Switzerland | Grey heron is protected |
United Kingdom | Kingfisher is protected. Licence may be given to shoot grey heron, cormorant, and lesser black-headed gull on fish farms, if predation is serious. |
See Part C - Research.
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:
Finland | National Veterinary Institute, Helsinki: Two-year old eye flukes have destroyed more than 10% of the fish population in three cases. |
Oulu Fish Farm: Damage of about Fmk 30 000 (US$ 5 600) was sustained in the summer of 1983. | |
Federal Republic of Germany | Bayern: DM 30 000/year/farm (US$ 12 500). |
Niedersachsen: DM 500 000/year (US$ 210 000). | |
Nordwürttemberg: Grey herons eat 118.6 t of the total yearly fish production and catch of 700 t. | |
Ireland | Losses are estimated at 27.5%. |
Netherlands | Losses are estimated at 10–20%. |
Poland | Loss for small fish are estimated at up to 20%. |
Switzerland | Fishfarmers guess an annual damage of Sw F 500.00–1 000.00 (US$ 250 000–500 000). |