SNP analyses and acoustic tagging reveal multiple origins and widespread dispersal of invasive brown trout in the Falkland Islands

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.

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

“…Several factors may help explain this. Firstly, our study shows that brown trout introduced into the Falkland Islands originated from at least four different origins with two life history strategies (anadromous, non-anadromous), which resulted in genetic admixture (Minett et al 2021b). It is known that multiple origins and genetic admixture can increase genetic diversity and facilitate adaptation to novel conditions (Consuegra et al 2011), which along with repeated introductions may increase invasion success.…”

“…It is known that multiple origins and genetic admixture can increase genetic diversity and facilitate adaptation to novel conditions (Consuegra et al 2011), which along with repeated introductions may increase invasion success. Establishment success may have also been facilitated by phenotypic plasticity and marine dispersal, as demonstrated recently by acoustic tracking (Davidsen et al 2021;Minett et al 2021b).…”

“…It may consist of two phases (Fig. 2), an initial phase characterized by rapid colonization, likely aided by low competition, fast growth and coastal dispersal (Jarry et al 2018;Labonne et al 2013;Minett et al 2021b), and a second, slower phase seemingly being driven by density-dependence (Labonne et al 2013). In Newfoundland, where brown trout is also invasive but where it competes with native Atlantic salmon, the species has expanded at rate of 4 km/year, and after ~ 135 years is still confined within a 500 km radius from the original sites of introduction (Westley and Fleming 2011).…”

“…A database of presence/absence records of the four species of freshwater fish present in the Falkland Islands (three native galaxiids, A. zebra, A. taeniatus, and Galaxias maculatus; and the non-native brown trout) was compiled by crosschecking records from McDowall et al (2001) and Ross (2009), supplemented with information from anglers and our own sampling (Fowler 2013;Minett et al 2021aMinett et al , 2021b. The survey by McDowall et al (2001) employed seine, gill and fyke netting, spotlighting at night, and electrofishing of ~ 50 m stream reaches.…”