The Use of Barriers to Limit the Spread of Aquatic Invasive Animal Species: A Global Review

Abstract

Aquatic invasive species (AIS) are one of the principal threats to freshwater biodiversity. Exclusion barriers are increasingly being used as a management strategy to control the spread of AIS. However, exclusion barriers can also impact native organisms and their effectiveness is likely to be context dependent. We conducted a quantitative literature review to evaluate the use of barriers to control animal AIS in freshwater ecosystems worldwide. The quantitative aspect of the review was supplemented by case studies that describe some of the challenges, successes, and opportunities for the use of the use of AIS exclusion barriers globally. Barriers have been used since the 1950s to control the spread of AIS, but effort has been increasing since 2005 (80% of studies) and an increasingly diverse range of AIS taxa are now targeted in a wide range of habitat types. The global use of AIS barriers has been concentrated in North America (74% of studies), Australasia (11%), and Europe (10%). Physical barriers (e.g., weirs, exclusion screens, and velocity barriers) have been most widely used (47%), followed by electric (27%) and chemical barriers (12%). Fish were the most targeted taxa (86%), followed by crustaceans (10%), molluscs (3%) and amphibians (1%). Most studies have been moderately successful in limiting the passage of AIS, with 86% of the barriers tested deterring >70% of individuals. However, only 25% of studies evaluated barrier impacts on native species, and development of selective passage is still in its infancy. Most studies have been too short (47% < 1 year, 87% < 5 years) to detect ecological impacts or have failed to use robust before-after-control-impact (BACI) study designs (only 5%). Hence, more effective monitoring is required to assess the long-term effectiveness of exclusion barriers as an AIS management tool. Our global case studies highlight the pressing need for AIS control in many ecoregions, and exclusion barriers have the potential to become an effective tool in some situations. However, the design and operation of exclusion barriers must be refined to deliver selective passage of native fauna, and exclusion barriers should only be used sparingly as part of a wider integrated management strategy.

Selective effects of small barriers on river‐resident fish

“…However, barriers to restrict invasive species should aim to provide for passage of native fauna to avoid the harmful effects of isolation (Rahel, 2013), and in this case, the use of even a small barrier would exclude upstream passage of all native fishes except brown trout. This highlights the difficulties of developing selective barriers for invasive species management (Jones, Tummers, et al, 2021;Rahel, 2013).…”

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

“…Mechanical removal of trout tends to increase the density of small fish (Meyer et al, 2006 ; Saunders et al, 2015 ) and is not an appropriate managing strategy, but they seem to be contained by beaver dams and natural competition at high densities of native fish (Budy & Gaeta, 2018 ). A combination of molecular markers, eDNA and acoustic tagging, as used here, can be employed to monitor the expansion of brown trout and put measures in place to limit its dispersal, for example through the installation of selective barriers (Jones et al, 2021 ).…”

Climate Change Effects on North American Fish and Fisheries to Inform Adaptation Strategies

“…Therefore, identifying areas for barrier removal (e.g., obsolete dams) to allow for connectivity, while also identifying where best management practices to control excessive nutrients may be useful (Johnson et al 2014; Solomon et al 2015); such management has led to more resilient lakes for cold‐water fish that require high quality oxythermal habitat (Jacobson et al 2013). However, increased connectivity may not be universally positive as this may facilitate invasive species (Jones et al 2021). Decision support tools that identify these stressors to determine when and where conservation efforts are best invested will continue to be important, because needs will undoubtedly outstrip limited resources (Peterson et al 2013; Tingley et al 2019).…”