This work to remediate barriers to fish migration is informed by the work of Project partners to understand their habitats. Te Hoiere has high freshwater biodiversity values with 14 species of native freshwater fish recorded, including two threatened and seven at-risk species. Several species of data deficient and threatened freshwater invertebrates have also been recorded in the catchment. The project’s work to remediate fish barriers will support ecosystems that are healthy, well-connected, and resilient.
Guided by science
This work is guided by science, starting with a desktop study by National Institute of Water and Atmosphere (NIWA), and catchment condition surveys undertaken by the community in partnership with Marlborough District Council.
Launched in 2020, Marlborough District Council's Catchment Care Programme began to provide catchment condition surveys throughout the district, including Te Hoiere. These were voluntary and made available to landowners at no charge. A surveyor mapped the area for water flows, including fencing, stream crossings, runoff areas and riparian plantings. Weed issues, wetland areas and culverts were also be identified, in line with national criteria for freshwater management.
Then in 2022, the National Institute of Water and Atmosphere (NIWA), undertook a desktop study of fish barriers in the catchment as well as priority areas for remediation. In 2023, work began to ground truth the study, find the high priority areas and start talking to the community about project funding for fish barrier remediation.
Types of barriers
Many of Te Hoiere’s freshwater fish have a special relationship with the ocean, with part of their lifecycles in both freshwater and saltwater. Barriers are a key cause of freshwater fish population decline, blocking species that must make their way to sea to mate or spawn.
Culverts with overhangs as short as 10cm can disrupt upstream travel, especially for fish that rely on low flow stretches to “burst” upstream to habitat where they can grow into adult fish. Sizing culverts appropriately for floodwaters, replicating stream gradients, and including natural substrate inside culverts improves fish passage while reducing erosion and downstream damage. Installing spoiler baffles or spat ropes inside culverts improves fish passage by reducing water speed and providing resting areas for migrating fish. Areas for improvement include:
- Raised (‘perched’) culverts or drains
- Rapids with steep gradients over 20 degrees
- Fast flowing water with no obvious resting places for fish
- Grates, gates or mesh that might block fish
- Waterfalls with a drop greater than 10cm
Through our partners Marlborough District Council and Department of Conservation, the Project is assessing barriers to fish passage in the catchment. Priority for available funding includes the amount of upstream catchment that isn’t accessible, known habitats of at-risk or threatened species, and severity of the barrier or whether it's cost-effective to fix.
Remediation through the Project can include support with:
- New culverts
- Spat ropes
- Spoiler baffles
- Rock ramps
- Fish ramps
- Culvert alternative
The modelling work by NIWA coupled with the catchment condition surveys has guided the Project on priorities for the fish barrier remediation programme. While support is available for remediation of some passages, the Project is currently working through priority areas. More funding is being identified for the future.
These culverts have been assessed in Te Hoiere catchment as high or very high risk to fish migration, as well as assigned a priority score for remediation support by the Project. Sites are prioritised by considering a number of factors, including cost effectiveness to remediate and risk to threatened native species.