Non-physical barriers to deter fish movements

Anthropogenic modifications to aquatic ecosystems have altered connecting pathways within, and in some cases, between watersheds. Human structures, such as hydroelectric facilities, often impede fish migrations and may inflict heavy mortality on fish that become impinged or entrained. Conversely, an increase in connectivity between two waterways (e.g.; through the construction of shipping canals, increased boat traffic) often results in an elevated risk of invasive species introductions. Non-physical barriers, which obstruct fish from an undesirable location without influencing the waterway, are one management approach to protecting valuable fish stocks and deterring biological invasions. Because many methods of behavioral deterrence have been employed against fish, there is a need to summarize and compare existing and developing technologies. This review details the use and application of electrical, visual, acoustic, chemical, and hydrological deterrence techniques that may be used to prevent fish movements. Site requirements are discussed, and a critical assessment of benefits and limitations to each technique are given. Because no single method of fish deterrence is "one size fits all", this review to non-physical fish barrier technology will benefit managers and researchers attempting to develop a best-fit strategy on a case-by-case basis.