The ancient and endemic river resident galaxiids are a fascinating and unique species of fish that are found only in New Zealand. These fish are close relatives of whitebait, but unlike their migratory cousins, they spend their entire lives in the same stream, sometimes even the same pool.
One of the most comprehensive studies to date on the effectiveness of conservation interventions aimed at protecting non-migratory galaxiids was conducted by PhD candidate Martha Jolly at the University of Canterbury. Her four-part thesis focuses on the use of trout exclusion barriers in New Zealand and its global implications.
The Threats Facing Galaxiids
- Habitat loss and climate change pose a significant threat to galaxiids
- The introduction of predatory trout has led to the decline of many populations
- Many populations have survived unchanged for thousands of years, but now face extinction
“These fish are part of our evolutionary story,” said Jolly. “They’re unique to Aotearoa, but most people have never heard of them, let alone seen them. They live out of sight and, too often, out of mind.”
Conservation Interventions
While New Zealand has led the way with physical trout exclusion barriers, Jolly’s research reveals that globally and nationally, there is little formal documentation of how these tools are used, or how well they work.
- Many interventions are reported in internal memos or agency reports, but rarely in scientific literature
- The lack of documentation makes it difficult for others to learn from or build on the work that’s already being done
Her work combines field measurements, population modelling, and a global meta-analysis to identify what makes a successful barrier.
Effective Barriers
| Barrier Type | Description | Benefits |
|---|---|---|
| Height | A large barrier can cause flooding in sensitive spring-fed systems | Limiting trout access while preserving habitats |
| Anti-jump screens | Limit trout access while preserving habitats | Preventing trout from jumping over barriers |
| Shallow plunge pools | Limit trout access while preserving habitats | Allowing native fish to thrive in shallow areas |
“Height is a key factor,” said Jolly, “but in sensitive spring-fed systems, large barriers can cause flooding.” Her team identified alternative techniques, such as anti-jump screens and shallow plunge pools, that limit trout access while preserving fragile habitats.
Broader Conservation Efforts
“Even where barriers have been in place for years, the populations above them are tiny, sometimes just a few hundred individuals,” said Jolly. “We’re not reversing decline; at best, we’re slowing it. If we don’t act fast with a broader toolkit; translocations, captive breeding, expanded reserves, then we risk monitoring these species into extinction.”
“There’s nowhere else in the world you can find this fish,” said Jolly. “If we lose it, it’s gone forever. The Galaxias cobitinis (lowland longjaw) is one of the most endangered, with fewer than 200 adults in each population.”
A Holistic Approach
“We’re not anti-trout,” said Jolly. “There’s space for both native species and introduced sport fish, but we need to make more space for native biodiversity than we are right now. We need a holistic toolkit. That means not just barriers in streams but legal protection, more resource allocation, better data sharing, and a cultural shift that brings underwater biodiversity into the national conservation story.”
“These fish are part of our evolutionary story. They’re unique to Aotearoa, but most people have never heard of them, let alone seen them.