Introduced species in lakes


Fishing in high mountain lakes: a traditional activity that turned into a conservation problem

In the Pyrenees, there has been a process of introduction and historical exploitation initially affecting approximately 25% of the lakes that goes back at least to the fourteenth and fifteenth centuries. These historical introductions used native trout fry from nearby rivers. During the second half of the twentieth century there was a significant increase in trout releases using large quantities of juvenile fish of different species from local fish farms. These modern practices have resulted in an increase in the proportion of high mountain lakes with fish, between 40% and 90% depending on the area.

At present 32% of the lakes in the SCI Alt Pallars and 75% in the SCI Aigüestortes have been stocked with fish. Salmonids introduced in the Pyrenees include brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis). The European minnow (Phoxinus sp.), a small Cyprinid, has also been introduced in many of the lakes in the Pyrenees, but in this case, the arrival is related with its use as live bait for fishing trout.

In the Italian Alps, 89% of the lakes in Mont Avic Natural Park and 35% in the Gran Paradiso National Park have been stocked with fish. The species introduced in Mont Avic Natural Park are Arctic char (Salvelinus alpinus), the European minnow (Phoxinus spp.), the Italian riffle dace (Telestes muticellus), brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss); and the species introduced in Gran Paradiso National Park are brook trout (Salvelinus fontinalis) and brown trout (Salmo trutta).

Fish habitat preferences partially or totally overlap those of the project target species (C. asper, A. obstetricans, R. temporaria, G. pyrenaicus), which spend all (the amphibians) or part (G. pyrenaicus) of their life in lakes and ponds for reproduction, larval development, feeding, etc. This overlap usually produces an exclusion pattern, where target species are brought to local extinction (by direct predation) or displaced (by predator avoidance) or elimination of resources (in the case of G. pyrenaicus) by fish. These introduced fish also affect terrestrial insectivores relying on aquatic food subsidies, such as bats (R. hipposideros, B. barbastellus, M. myotis, M. blythii, M. bachsteini, N. lasiopterus and P. macrobullaris). Therefore, fish introduction is the main threat for these target species in high mountain lakes.

Brook trout

Salvelinus fontinalis
Allochthonous | Introduced in lakes

Brown trout

Salmo trutta
Allochthonous | Introduced in lakes

Danubian minnow

Phoxinus csikii
Allochthonous | Introduced in lakes

Garonne minnow

Phoxinus dragarum
Allochthonous | Introduced in lakes

Languedoc minnow

Phoxinus septimaniae
Allochthonous | Introduced in lakes


Phoxinus spp.
Allochthonous | Introduced in lakes

Rainbow trout

Oncorhynchus mykiss
Allochthonous | Introduced in lakes