Conservation of endangered galaxiid fishes in the Falkland Islands requires urgent action on invasive brown trout

Non-native salmonids are protected in the Southern hemisphere where they sustain aquaculture and lucrative sport fisheries, but also impact many native fishes, which poses a conservation conundrum. Legal protection and human-assisted secondary releases may have helped salmonids to spread, but this has seldom been tested. We reconstructed the introduction of brown trout (Salmo trutta) to the Falkland Islands using historical records and modelled its dispersal and probability of invasion using a generalized linear model and Leave One out Cross Validation. Our results indicate that establishment success was similar to 88%, and that dispersal was facilitated over land by proximity to invaded sites and density of stream-road crossings, suggesting it was human assisted. Brown trout have already invaded 54% of Falkland rivers, which are 2.9-4.5 times less likely to contain native galaxiids than uninvaded streams. Without strong containment we predict brown trout will invade nearly all suitable freshwater habitats in the Falklands within the next similar to 70 years, which might put native freshwater fishes at a high risk of extinction.

Automated summary

Non-native salmonids are protected in the Southern hemisphere, but they pose a threat to native fishes. The introduction and spread of brown trout in the Falkland Islands have been facilitated by human assistance. Without containment measures, brown trout may invade almost all suitable freshwater habitats in the Falklands, putting native freshwater fishes at risk of extinction.