Brown trout - among 100 "world’s worst" invaders

Authors: Invasive Species Specialist Group of the International Union for Conservation of Nature

The brown trout is one of the fish causing most harm when introduced as an alien species. Across the globe, reckless anglers are to blame.

This species has been nominated as among 100 of the "World’s Worst" invaders."


anglers encourage alien fish - brown trout

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"Introduced around the world for aquaculture and stocked for sport fisheries. It is blamed for reducing native fish populations, especially other salmonids, through predation, displacement and food competition. It is a popular angling fish."

"Brown trout have been implicated in reducing native fish populations (especially other salmonids) through predation, displacement, and food competition."

Location-Specific Impacts
This is an edited-down list from the database.

Australia
Predation: The impact of predation by brown trout on many native species, especially representatives of the family galaxiidae, has been severe.

Tasmania
Predation: May have caused the decline of the Tasmanian mountain shrimp Anaspides tasmaniae. The impact of predation by brown trout on many native species, especially representatives of the family galaxiidae, has been severe.

Victoria (Australia)
Predation: The brown trout may have caused the decline of the Tasmanian mountain shrimp Anaspides tasmaniae, and has eliminated or reduced several Plecoptera and Trichoptera in Victorian streams (Fishbase, 2003). The impact of predation by brown trout on many native species, especially representatives of the family galaxiidae, has been severe.

Falkland Islands (Malvinas)
Reduction in native biodiversity: Native zebra trout have suffered massive declines since the introduction of brown trout and remain largely in restricted areas where brown trout have not yet invaded (including some land-locked freshwater populations). The introduced trout are migratory and it is considered likely that they will eventually invade all the streams currently inhabited only by zebra trout.

Italy
Hybridisation: North Italy (Croatia also) has an endemic trout, Salmo marmoratus, which creates fertile hybrids with the brown trout. Nowadays, it is very hard to know if a trout is a hybrid or not.

Japan
Competition: Many species of salmonids have been introduced into streams throughout the world, primarily for recreational fishing.

New Zealand
Predation: The impact of the introduction on native fish has been apparent in reduction of riverine and lake populations of galaxiids. The native eleotrid fauna remain an important prey item of trout.

Michigan (USA) Competition: Adult brown trout displaced adult native brook trout from the best habitats in a Michigan stream.

Fish Pain