INVASIVE FISH, ALTERED 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

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Brook trout

Salvelinus fontinalis (Mitchill, 1814)

Origin: Allochthonous

Habitat: Introduced in lakes

Is a species native to Eastern North America. Originally live in rivers and lakes very cold which allows it to adapt very well to the lakes of the Pyrenees. Today has been introduced to all continents.

Brown trout

Salmo trutta
Allochthonous | Introduced in lakes

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Brown trout

Salmo trutta (Linnaeus, 1758)

Origin: Allochthonous

Habitat: Introduced in lakes

In addition to native brown trout of mountain rivers, high mountain lakes have also been introduced with Central European varieties of brown trout that had been adapted to reproduce on farms.

Danubian minnow

Phoxinus csikii
Allochthonous | Introduced in lakes

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Danubian minnow

Phoxinus csikii (Hankó, 1922)

Origin: Allochthonous

Habitat: Introduced in lakes

P.csikii has been found in the high mountain lakes of the Italian Alps.

Garonne minnow

Phoxinus dragarum
Allochthonous | Introduced in lakes

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Garonne minnow

Phoxinus dragarum ((naua espècia))

Origin: Allochthonous

Habitat: Introduced in lakes

Phoxinus dragarum is the only species of minnow detected in the high mountain lakes of the Pyrenees, specifically in the lakes of Aigüestortes and Estany de Sant Maurici National Park and L’Alt Pirineu Natural Park. This species of minnow has also been detected in the rivers of Catalonia and the French Garonne.

Languedoc minnow

Phoxinus septimaniae
Allochthonous | Introduced in lakes

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Languedoc minnow

Phoxinus septimaniae (Kottelat, 2007)

Origin: Allochthonous

Habitat: Introduced in lakes

P. septimaniae has been found in the high mountain lakes of the Italian Alps.

Minnow

Phoxinus spp.
Allochthonous | Introduced in lakes

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Minnow

Phoxinus spp. (Rafinesque, 1820)

Origin: Allochthonous

Habitat: Introduced in lakes

It is a small cyprinid less than 12 cm in length used as bait for trout fishing and more recently introduced in high mountain lakes by fishermen themselves. It is gregarious behavior and competes with trout since it has the same diet.

Rainbow trout

Oncorhynchus mykiss
Allochthonous | Introduced in lakes

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Rainbow trout

Oncorhynchus mykiss (Walbaum, 1792)

Origin: Allochthonous

Habitat: Introduced in lakes

Is a species native to native to cold-water tributaries of the Pacific Ocean. As with trout is one of the 100 most invasive species in the world. Used for restocking since the late nineteenth century. There are different subspecies adapted to living in the sea, rivers and lakes