Abstract
Biological invasions are important causes of biodiversity loss, particularly in remote islands. Brown trout (Salmo trutta) have been widely introduced throughout the Southern Hemisphere, impacting endangered native fauna, particularly galaxiid fishes, through predation and competition. However, due to their importance for sport fishing and aquaculture farming, attempts to curtail the impacts of invasive salmonids have generally been met with limited support and the best prospects for protecting native galaxiids is to predict where and how salmonids might disperse. We analysed 266 invasive brown trout from 14 rivers and ponds across the Falkland Islands as well as 32 trout from three potential source populations, using a panel of 592 single nucleotide polymorphisms (SNPs) and acoustic tagging, to ascertain their origins and current patterns of dispersal. We identified four genetically distinct clusters with high levels of genetic diversity and low admixture, likely reflecting the different origins of the invasive brown trout populations. Our analysis suggests that many trout populations in the Falklands may have originated from one of the donor populations analysed (River Wey). The highest genetic diversity was observed in the rivers with the greatest number of introductions and diverse origins, while the lowest diversity corresponded to a location without documented introductions, likely colonized by natural dispersal. High levels of gene flow indicated widespread migration of brown trout across the Falkland Islands, likely aided by anadromous dispersal. This is supported by data from acoustically tagged fish, three of which were detected frequently moving between two rivers ~26 km apart. Our results suggest that, without containment measures, brown trout may invade the last remaining refuges for the native endangered Aplochiton spp. We provide new insights into the origin and dispersal of invasive brown trout in the Falkland Islands that can pave the way for a targeted approach to limit their impact on native fish fauna.
Highlights
The spread of invasive species can occur via accidental introduction, deliberate release and/or natural processes
The results of the Discriminant Analysis of Principal Components (DAPC) analysis of samples from both the Falkland Islands and Great Britain indicated the existence of five genetically distinct clusters (Figure 3b and Figures S2b and S3b), the 4 clusters identified in the Falklands-only analysis and one additional cluster (5), which consisted of individuals from Loch Leven and the Howietoun hatchery (Figure 3)
Our analysis revealed the presence of four genetically distinct clusters of invasive brown trout in the Falkland Islands, likely reflecting their different origins, we cannot discard the effects of founder effects on the structuring
Summary
The spread of invasive species can occur via accidental introduction, deliberate release and/or natural processes. Brown trout (Salmo trutta) is native to Europe, Western Asia and Northern Africa; since 1864, it has been widely introduced outside of their native range and is currently found on all continents except Antarctica (MacCrimmon & Marshall, 1968) Such introductions have resulted in extensive ecological damage making brown trout one of the 100 world's worst invasive species (Lowe et al, 2000). The exact sources of the Pentlands stock are unknown but believed to originated from Cobbinshaw Loch or Loch Leven (Minett et al, 2021) Since their introduction, brown trout have widely spread throughout East and West Falklands (Fowler, 2013; McDowall et al, 2001; Minett et al, 2021). We used a panel of single nucleotide polymorphisms (SNPs) and acoustic telemetry, to assess population structuring, potential origins of the current brown trout populations and levels of migration and gene flow among them, to establish their patterns of dispersal
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