Data from: Hitt et al. 2026 "Swimming under the radar: Trout-free kōaro populations in Aotearoa lakes and tarns are rare, understudied, and disappearing"

These datasets are the data complementary to this article:Hitt, L.G., S.D. Stewart, N.C. Boddy, and A.R. McIntosh. 2026. Swimming under the radar: Trout-free kōaro populations in Aotearoa lakes and tarns are rare, understudied, and disappearing. New Zealand Journal of Marine and Freshwater Research https://doi.org/10.1002/nzm2.70036.Article 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 These systems require more research because our existing knowledge is outdated, patchy, and largely unacknowledged, while their kōaro populations may increasingly vulnerable Although persisting trout-free kōaro populations tend to be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.Files and descriptions:koaro_only_lake_characteristics.xlsx A dataset of Aotearoa lakes believed to contain trout-free populations of kōaro (Galaxias brevipinnis) and their abiotic characteristics, such as lake altitude, depth, and area. Lakes were identified using the New Zealand Freshwater Fish Database (NZFFD; https://niwa.co.nz/freshwater/nz-freshwater-fish-database) and consulting with local freshwater fish experts. lakes_field_survey_data.xlsx A dataset of the results of fish trapping surveys at a subset of Aotearoa lakes believed to contain trout-free populations of kōaro (Galaxias brevipinnis); these data indicate which lakes were sampled, how many times each lake was sampled, what traps (and how many traps) were used, and how many fish of each species were caught.