A10. Resistivity fish counter

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Resistive Counter Diagram, © Loughs Agency (2016)

1. Objectives

  • Accurately count the genitors in anadromous migratory fish communities.
  • Obtain information on phenology and migration patterns – relating to environmental factors (temperature, flow etc.) – and on upstream and downstream migration.
  • Assess population size.
  • Evaluate function of fishways.
  • Use low cost devices to assess narrow streams.

2. Method summary

The resistivity counter counts fish by taking advantage of the difference in electrical resistance between water (more resistant) and fish (less resistant). They are widely used throughout the UK (Eatherley et al., 2005). ‘Bulk resistance’ is where the resistance between two electrodes is constant at any given depth, temperature, and conductivity (Braun et al., 2016). When fish pass over or through the electrodes, a reduction of electrical resistance is detected, relative to the fishes’ size (proportional to resistance). If the signature fits a recognisable fish pattern, the counter records a fish (Coyle and Reed, 2012). Three stainless steel electrodes (at downstream, middle and upstream positions) are needed for the algorithm to determine size and swimming direction. Several types of resistivity counters are available: crump weir, flat pads, box sensors, and tube counters (Braun et al., 2016). Due to their adaptability, resistivity counters can be used in many configurations (e.g. weirs, natural rivers, fishways) and have been extremely useful to assess and stop the hard decline of Atlantic and Pacific salmon populations (Eatherley et al., 2005). A camera can be coupled with the system to confirm passing fish.

3. Advantages

  • Very good information for upstream and downstream salmonid counts.
  • Adaptable to site configuration.
  • Robust data collection; 97% accuracy in some studies (Freshwater Biological Association, 2015; Loughs Agency, 2016). For example, 94% accuracy average for upstream and 74% downstream migration (McCubbing and Ignace, 2000).
  • No fish handling therefore less fish stress.
  • Possible to dispatch data remotely.
  • Less expensive than installation of video-counting systems.
  • Low operational costs following installation.
  • Minimal annual maintenance.
  • Can cover the entire river width without the need of funnelling devices (fences or barriers).

4. Disadvantages

  • Environmental conditions such as water depth and conductivity can affect detection probability. This should be assessed before the survey to measure sensor accuracy (Forbes et al., 2000).
  • Expensive as the design varies from one site to another.
  • Usually does not give good information on the use of special tributaries by spawning salmonid populations. It is usually installed on the main channel of the river basin to gain quantitative information.
  • Material and design is generally heavy future improvements will likely reduce the cost and weight (Smith, et al. 1996).

5. Recommendation for method application

  • Anticipate the construction of the device before building the weir or fishway.
  • Use in downstream reaches of the river basin and analyse tributaries using other methods.
  • Register local environment data (water flow, temperature, depth) and link to fish passage.
  • Test internet connection and remote access to data or anticipate the installation of a computer in-situ with data storage.
  • Monitor the bulk resistance and evaluate these changes against algorithms to establish fish passage events. Some brands allow this (Braun et al., 2016).
  • Record instances of branches, high waves caused by wind, or ice to avoid erroneous data (false positive records of fish).

6. Cost

Between £10,000 and £20,000, but variable depending on civil engineering facilities characteristics. Cost estimate can be found in Braun et al. (2016).

7. Protocols and data analysis

  • Salmonid abundance, population phenology and cohort’s assessment.
  • Recruitment, if the resistivity counter is on the entire width of the stream and able to count downstream migrating juveniles.
  • Adult survival after reproduction (only for salmonid streams).

8. References

  1. Braun, D. et al. (2016) ‘Technical , Logistical , and Economic Considerations for the Development and Implementation of a Scottish Salmon Counter Network’, Scottish Marine and Freshwater Science, 7(2), p. 262. doi: 10.7489/1689-1.
  2. Coyle, C. L. and Reed, D. J. (2012) Assessment of the Performance of a Flat Panel Resistivity Fish Counter at Peterson Creek , 2007 and by.
  3. Eatherley, D. M. R. et al. (2005) Trends in Atlantic salmon: the role of automatic fish counter data in their recording. Commissioned Report No. 100.
  4. Forbes, H. E., et al. (2000) ‘An Assessment of the Performance an Assessment of the Performance of the Resistivity Fish Counter in the Borland Lift Fish Pass At Kilmorack Power Station On The River BeauLY’, Fisheries Research Services Report No 5/99.
  5. McCubbing, D. J. F. and Ignace, D. (2000) Salmonid Escapement Estimates on the Deadman River, resistivity counter video validation and escapement estimates., Enstream Fisheries Consultants.
  6. Smith, I. P. et al. (1996). Evaluation of a portable electrode array for a resistivity fish counter. Fisheries management and ecology, 3(2), 129-141.
  7. https://www.fba.org.uk/fish-counter
  8. https://www.wthwildlife.com/single-post/2017/02/26/Field-Tech-Resistive-Fish-Counters
  9. https://www.loughs-agency.org/managing-our-loughs/monitoring/fish-counter-programmes/