1. Water Quality Probe
How it was used
The probe was calibrated prior to use and then placed into flowing sections of the stream at mid-depth to avoid surface warming effects and sediment disturbance. Readings were allowed to stabilise before recording temperature, pH, dissolved oxygen (DO), and conductivity. Measurements were taken at multiple points to account for small-scale variation in water chemistry.
Why it was used
Water quality strongly influences eel physiology and habitat suitability. While eels are more tolerant than many native fish species, prolonged exposure to poor water quality can reduce growth rates, increase stress, and limit successful migration. Measuring these parameters allows environmental conditions to be linked directly to eel presence, size, and condition.
What it helps show
pH
Optimal range for eels: ~6.5–8.0
Poor / stressful: < 6.0 (acidic) or > 8.5 (alkaline)
Low pH can damage gill tissue and disrupt ion balance, while high pH can increase ammonia toxicity.
Conductivity
Healthy freshwater range: ~50–300 µS/cm
Elevated / poor: > 400–500 µS/cm
High conductivity often indicates nutrient enrichment, urban runoff, or salinity intrusion, which can degrade eel habitat quality.
Dissolved Oxygen (DO)
Good: > 6 mg/L
Poor: < 4 mg/L
Although eels can tolerate low oxygen better than most fish, persistently low DO increases stress and reduces activity.
Temperature (C)
Water temperature was measured using the water quality probe, which was placed at mid-depth in flowing water and allowed to stabilise before recording. Temperature was measured alongside other water quality variables for consistency.
Temperature influences eel metabolism, activity, and growth, as eels rely on surrounding water to regulate body processes. It also affects dissolved oxygen levels and food availability.
- Optimal range: ~12–20°C
- Stressful conditions: < 8°C or > 20°C
Water temperature helps indicate whether a stream provides suitable conditions for eel feeding, breathing,movement, and long-term habitat quality.
Together, these measurements indicate whether the stream provides a chemically suitable environment for sustaining eel populations and help identify possible catchment scale impacts.
2. Fyke Net (Hīnaki)
How it was used
The fyke net (hīnaki) was set overnight with the entrance facing downstream or perpendicular, positioned along natural eel movement pathways such as stream margins and deeper channels. Nets were checked promptly to minimise stress. Captured eels were identified to species, measured for length, and assessed for condition before release.
Why it was used
Fyke nets are effective because they exploit eel movement behaviour rather than relying on attraction or bait. The hīnaki also reflects long-standing Māori knowledge of eel ecology, reinforcing culturally informed monitoring practices.
What it helps show (specific data collected)
- Presence and abundance of eels in the stream
- Size and age structure, indicating whether the stream supports juveniles, adults, or migrants
- Species composition, supporting biodiversity assessment
- Movement patterns, suggesting how eels use different parts of the habitat
3. Dissection Kit
How it was used
The dissection kit was used to carefully examine eel specimens under controlled conditions. External features such as body condition, skin integrity, and fin damage were recorded. Internal examination focused on the digestive tract and major organs to assess feeding status and overall health.
What it helps show (specific indicators)
Stomach contents
Indicates recent feeding success and available prey
Fat reserves and organ condition
Reflect nutritional status and habitat quality
Signs of disease or parasites
May indicate environmental stress or degraded conditions
Developmental stage
Supports understanding of whether the habitat is used for growth, residency, or migration
Why it was used
Dissection allows direct observation of biological indicators that reflect both environmental quality and eel life history. Internal condition can reveal long-term stressors that are not immediately apparent from water quality data alone.
4. Humane Handling (Clove oil)
Alternative method – Ice
An alternative humane method is placing the eel into an ice slurry (a mix of ice and water), which gradually lowers body temperature and slows metabolism. This reduces activity and responsiveness, leading to loss of consciousness with minimal stress when performed correctly.
What it helps show
- Stress minimisation
Reduces physiological stress responses such as excessive movement, mucus loss, and oxygen demand during handling.
- Ethical euthanasia or sedation
Ensures the eel loses consciousness rapidly and painlessly before any invasive procedures, meeting animal welfare standards.
- Reliable biological observations
Calm, sedated eels allow more accurate assessment of size, condition, and internal organs without stress-related distortion.
- Consistency across samples
Standardised sedation improves comparability between specimens by limiting handling-induced variation.
How it's used
Clove oil (eugenol) was prepared as a dilute solution and added to a container of stream water. Eels were gently placed into the solution and monitored closely. Within a short period, the eel became sedated and unresponsive to external stimuli, indicating loss of consciousness. For euthanasia, the eel remained in the solution for a sufficient duration to ensure death before any dissection occurred. Throughout the process, handling was minimised and monitoring was continuous to ensure the procedure was humane and effective.
Why it's used
Clove oil is a widely accepted, humane anaesthetic for fish and eels. It is effective at low concentrations, acts quickly, and causes minimal distress when used correctly. Using clove oil aligns with ethical research practices, animal welfare guidelines, and kaupapa Māori principles of respect for living organisms. Humane handling ensures that data collected reflects true environmental and biological conditions rather than stress responses caused by poor handling.
5. Environmental DNA (eDNA) Sampling (OPTIONAL)
How it was used
Water samples were collected upstream of physical sampling areas to avoid contamination from captured or handled eels. Sterile bottles were used, and samples were sealed immediately. Samples were filtered and analysed in a laboratory to amplify eel-specific DNA markers.
Why it was used
eDNA is particularly effective for detecting species that are elusive, nocturnal, or present at low densities. It complements physical capture methods by reducing sampling bias and eliminating the need to disturb habitat or organisms during detection.
What it helps show (specific outcomes)
- Confirms presence or absence of eels within the catchment
- Detects eels even if they are burrowed, inactive, or avoiding traps
- Provides evidence of habitat use across time, as DNA can persist in water for days
- Helps validate or explain fyke net results (e.g., eDNA present but no capture suggests low abundance or trap avoidance)
6. Mauri Compass App
How it was used
The Mauri Compass App was used in the field to record all observations, measurements, and monitoring results in real time. Data collected from the water quality probe, eDNA sampling, fyke netting, and visual site observations were entered directly into the app during the assessment. The app guided the assessment process by prompting users to consider multiple environmental attributes rather than focusing on a single indicator.
Why it was used
The Mauri Compass App is designed to support holistic environmental assessment grounded in Te Ao Māori. Rather than relying solely on numerical data, the app integrates scientific measurements with cultural and observational indicators. This ensures that decision making reflects not just physical water quality, but also ecosystem health, mahinga kai values, and the wellbeing of people connected to the site.
Using the app in real time reduces data loss, improves accuracy, and allows immediate reflection on site conditions. It also encourages consistent assessment between sites and observers.
What it helps show
The Mauri Compass App helps interpret environmental data within a holistic framework of mauri . By combining quantitative measurements with qualitative observations, the app provides an overall indication of ecosystem health.
Specifically, it helps to:
- Assess whether the mauri of the waterway is being sustained, enhanced, or degraded
- Identify trade offs between environmental health, cultural values, and human use
- Support culturally informed decision-making for freshwater management
- Communicate results clearly to communities, kaitiaki, and decision makers
7. Water Clarity Tube
How it was measured
Water clarity was measured using a clarity tube. Stream water was poured into the tube until the black-and-white target at the base became visible. The depth at which the target could be seen was recorded as the clarity measurement.
Why it was measured
Clarity is an important indicator of sediment levels and disturbance within the catchment. While eels are tolerant of lower clarity than many fish species, excessive suspended sediment can smother habitat, reduce invertebrate abundance, and affect gill function.
What it helps show
- Good clarity: typically > 1.0 m
- Moderate clarity: 0.5–1.0 m
- Poor clarity: < 0.5 m
Low clarity often reflects upstream erosion, stock access, or runoff following rainfall. Reduced clarity can limit prey availability and degrade benthic habitat used by eels for shelter and feeding.
8. Stream Velocity
How it was measured
Stream velocity was measured by marking a 10-metre section of the stream. A floating object such as a lemon or orange was released at the upstream point and the time taken to travel the 10 metres was recorded using a stopwatch. This was repeated multiple times and an average time was calculated. Velocity was then estimated using the formula:
Velocity = Distance ÷ Time
Why it was measured
Stream velocity influences eel movement, energy expenditure, and habitat use. Eels prefer slow to moderate flows where they can move efficiently, shelter behind structures, and forage effectively. Velocity also affects sediment transport and channel stability.
What it helps show
- Low velocity: suitable for juvenile and resident eels, providing refuge and feeding areas
- Moderate velocity: supports migration and oxygenation
- High velocity: may limit eel movement and reduce habitat availability
Velocity measurements help explain eel distribution within the stream and provide context for fyke net placement and capture success.
Mauri Compass Equipment Used for Eel (Tuna) Monitoring