Ngāi Tai Stream Health Assessment
Fish Communities, Water Quality, Macroinvertebrates, and Flow Conditions Using the Mauri Compass – SHMAK Framework
Assessment period: 16–17 December 2025
He karakia kia uru ki ngā taiao
Ka urua te tāhū nui o Rangi
Ka urua te nuku roa o Papa
Tēnei te toki whakaaraara
He toki mā te tangata ora
Huia mai ki ahau
Huia mai ki te katoa
He mauri tōnui
Whakaputahia ki te whaiao,
ki te ao mārama!
Ka urua te nuku roa o Papa
Tēnei te toki whakaaraara
He toki mā te tangata ora
Huia mai ki ahau
Huia mai ki te katoa
He mauri tōnui
Whakaputahia ki te whaiao,
ki te ao mārama!
Whano, whano!
Haeremai te toki
Haumi ē!
Hui ē!
Tāiki ē!
Haeremai te toki
Haumi ē!
Hui ē!
Tāiki ē!
Nā Herea Winitana
Whānau
Mauri Compass Whare and Framework
Section 1
Introduction
Freshwater stream health is best understood through the integration of multiple indicators that reflect chemical, biological, and physical conditions. No single metric can adequately capture ecosystem condition in isolation.
This assessment applies the Mauri Compass – Stream Health Monitoring and Assessment Kit (SHMAK) to evaluate stream health using four complementary components:
Fish communities
(with emphasis on tuna / longfin eel)
Water quality
(pH, temperature, conductivity)
Macroinvertebrate communities
(MCI / QMCI)
Flow characteristics
(velocity and discharge)
Mahinga Kai
(mahi ngā kai)
Wairua
(karakia)
Together, these indicators provide a robust picture of ecological integrity, habitat suitability, and mauri across the stream system.
Day 1
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Section 2
Methods Overview
Assessments were undertaken across multiple sites between 14 and 17 December 2025.
Fish surveys
Conducted at Sites 2–5 using baited methods suited to nocturnal and cryptic species.
Water quality measurements
Collected at Sites 1–5 using in-situ field instruments.
Macroinvertebrate Community Index (MCI) surveys
Undertaken at two locations, including Site 1 and an additional site with unspecified location.
Flow measurements
Recorded at the Waiting Bridge site using SHMAK flow assessment protocols.
All data were interpreted using SHMAK and Mauri Compass guidelines aligned with New Zealand freshwater standards.
Section 3
Fish Community Assessment
3.1 Species Presence
Across all fish survey sites (Sites 2–5), longfin eel (Anguilla dieffenbachii) was the only species recorded.
All individuals observed were native, with no introduced fish detected, indicating maintained ecological connectivity and an absence of invasive fish pressure.
3.2 Abundance and Size Structure by Site
Site 2
Nine adult longfin eels were captured at Site 2.
- Measured lengths ranged from approximately 41 cm to 97 cm, including at least one very large individual.
- Abundance was classified as common.
- The presence of multiple large-bodied adults suggests long-term habitat stability and sustained access to migration pathways.
Day 2
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Site 3
Nine adult eels were also recorded at Site 3, with lengths ranging from approximately 30 cm to 55 cm.
While individuals were generally smaller than those at Site 2, eels at this site were described as notably lively and active, suggesting favourable local habitat conditions, such as good oxygen availability and effective refuge habitat.
Site 4
Site 4 recorded the highest abundance, with eleven adult eels measured between approximately 39 cm and 58 cm.
Despite high numbers, many individuals appeared lethargic, indicating that although the site remains accessible and capable of supporting eels, localised stressors may be influencing fish condition.
This may reflect sediment accumulation, reduced flow variability, or organic enrichment rather than chemical pollution.
Site 5
Only one adult eel was recorded at Site 5, measuring approximately 64 cm.
Water at this site was described as significantly more turbid.
While the eel appeared healthy and active, the low abundance suggests that habitat quality or carrying capacity may be reduced at this location, likely due to suspended sediment or runoff inputs.
3.3 Fish Community Interpretation
Under SHMAK guidelines, the presence of a single native species corresponds to a "fair" ecological condition.
However, the consistent occurrence of adult longfin eels—a long-lived, nationally threatened taonga species—indicates that the stream continues to function as important habitat.
Spatial differences in abundance and behaviour strongly suggest that physical habitat conditions, rather than water chemistry, are the primary drivers shaping eel distribution.
Section 4
Water Quality Assessment
Water quality was assessed at Sites 1–5 and showed consistently favourable results across the catchment.
pH
Ranged from 6.97 to 7.18, well within optimal ranges for native freshwater fauna.
Temperature
Ranged from 16.3°C to 19.5°C, remaining below stress thresholds and supportive of high dissolved oxygen levels.
Conductivity
Values ranged from 72 to 142 µS/cm, with most sites classified as pristine and no evidence of significant pollution.
Overall, water chemistry across all sites was excellent, indicating no major chemical constraints on aquatic life.
Section 5
Macroinvertebrate Community (MCI) Assessment
5.1 MCI Assessment – High-Quality Site
One MCI assessment recorded a score of 6.7, classifying the site as excellent.
Two taxa were identified:
- Green stonefly (Stenoperla) – score 10, abundance 1
- Dolomedes spider – score 5, abundance 2–5
Stoneflies are highly sensitive to pollution and habitat degradation, and their presence strongly indicates pristine water quality and stable habitat conditions. Despite low taxa richness, the dominance of sensitive taxa supports the high MCI score.
5.2 MCI Assessment – Site 1
At Site 1, the MCI score was 4.3, classifying the site as poor under QMCI guidelines.
Two taxa were recorded:
- Freshwater shrimp (Paratya) – abundant (21+ individuals)
- Flat spiral snail (Gyraulus) – moderate abundance
Both species are relatively tolerant of environmental stress, and their dominance suggests reduced habitat quality. This result contrasts with the strong water chemistry at Site 1, indicating that habitat structure, sedimentation, or flow disturbance may be limiting invertebrate diversity despite acceptable chemical conditions.
Photo of a macroinvertebrate and an Elver that students found
Section 6
Flow Assessment
Flow measurements were conducted at Waiting Bridge, recording a mean velocity of 1.001 m/s and a discharge of approximately 2.0 m³/s (2002 L/s).
1.001
Mean velocity
metres per second
2.0
Discharge
cubic metres per second (2002 L/s)
High flows can reduce habitat stability, dislodge macroinvertebrates, and limit refuge availability for fish, particularly in simplified channels.
Section 7
Integrated Stream Health Discussion
When considered together, results show a system with excellent water chemistry, strong native fish presence, but variable biological responses driven by physical habitat and flow conditions.
Longfin eels are present throughout the system
indicating maintained connectivity.
Macroinvertebrate results vary sharply between sites
suggesting localised habitat degradation rather than catchment-wide pollution.
From a Mauri Compass perspective, the stream retains strong mauri overall.
Section 8
Conclusion
This integrated SHMAK assessment demonstrates that the stream system maintains high water quality, and mauri, and continued support for taonga species, particularly longfin eel.