Swimming Under the Radar: Trout‐Free Kōaro Populations in Aotearoa Lakes and Tarns Are Rare, Understudied, and Disappearing

Abstract

Over the last 150 years, most large, easily accessible lakes and tarns in Aotearoa (New Zealand) have experienced trout introductions or incursions, leaving few salmonid‐free reference lakes. Using database information and field surveys, we characterized lake, pond/tarn, and wetland systems found throughout Aotearoa that support populations of kōaro ( Galaxias brevipinnis ) known or putatively believed to be trout‐free. These systems require more research because our existing knowledge is outdated, patchy, and largely unacknowledged, while their kōaro populations may be increasingly vulnerable. Although persisting trout‐free kōaro populations tend to be found in small, isolated, and difficult to access lakes, at least 10% and potentially up to 22% of known trout‐free kōaro populations may have already been lost in the last 20 years. The causes of these losses are varied and highlight the sensitivity of the remaining populations, which are likely genetically isolated and evolutionarily significant. Historic and modern threats to these remaining kōaro populations include incursions of introduced fishes and worsening climate impacts. Lakes supporting isolated kōaro populations hold substantial conservation value, require more consistent monitoring to prevent additional losses of irreplaceable populations, and need targeted conservation of this important taonga (treasured species) consistent with the diversity they contribute to Aotearoa's broader freshwater biodiversity.

Bibliographic Information