Introduction: New Zealand has around 51 species of native freshwater fish, with an additional 3 colonist species and 20 introduced species that are now considered naturalised in New Zealand waters (Allibone et al., 2010). Some of New Zealand’s native fish are vulnerable to direct predation and/or competition by introduced, invasive species, as well as adverse changes to aquatic habitat caused by these introduced species (Rowe and Dean-Speirs, 2009). Many species are diadromous, moving between freshwater and salt water during their life cycle, and the ability to migrate between streams, lakes and the sea is therefore vitally important to their population health (McDowall, 2000), while there are also a number of non-diadromous species that are specialised to specific habitats. It has long been recognised that dams prevent fish migration and consequently there has been much research conducted into overcoming these barriers to ensure fish passage. However, the vulnerability of New Zealand’s native fish and other aquatic values, e.g. macrophytes, to invasive species suggests some barriers, whether natural or built, could be used to create protected habitats for some native species in key locations. Kates et al. (2012) noted that “rather than try to eliminate invasive species after introduction, preventing their spread is a more efficient strategy to mitigate impact.” Waterway barriers in some locations provide a means of preventing spread of invasive fish species naturally, while in other locations natural barriers have been enhanced or barriers installed to facilitate the removal of invasive species from key native locations to create protected areas.

Scope of Review: This review collates international and New Zealand experience to date of built barriers and New Zealand natural barriers that protect native fish and other values by exclusion of invasive species, predominately trout. This review aims to summarise current knowledge of the following questions:

1. What types of barriers exist?
2. What is the known effectiveness of each of these types of barrier?
3. What design components are necessary to create an effective barrier to control movement of certain species upstream?
4. What does experience suggest would be most effective for protection of New Zealand’s native fish species? Most fish passage and barrier management publications in New Zealand have focused on how to reduce or remedy the impacts of barriers to fish migration (i.e. promote fish passage), whereas this review focuses on specific situations where barriers should be maintained or built to protect native values. The focus of this work is on small scale structures (<4 m in height). This review encompasses English-language peer-reviewed literature.