A10. Acoustic telemetry

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1. Applicability and Purpose

This method is designed for tracking fish with a high temporal and spatial accuracy in order to:

  • Evaluate fish behaviour related to habitat (Bergé, 2012), including home range extent on long river reaches and use of tributaries.
  • Study fish migration (speed, resting areas, obstacles), presence on spawning grounds and residence time.
  • Evaluate the presence of barriers to fish passage.

2. Method Description

Acoustic telemetry is designed to track fish over a river’s length or specific site. An active tag emitter implanted or attached to the fish gives its position to one or several (an acoustic array) receivers, called ‘hydrophones’, placed at spots of interest for passive monitoring. Active monitoring can be done by using a hydrophone on a vessel (Capra et al., 2018). Acoustic telemetry is versatile and has been used successfully in different environmental settings, from inland rivers and estuaries to coastal waters and the open ocean (Thorstad et al., 2013). The nature of acoustic wave propagation results in the technology being most efficient in marine, estuarine and moderate-high conductive freshwater environments with low turbulence, no entrained air and reduced background underwater noise. Capturing and handling fish is often necessary to implant the tag, which is implanted internally via surgical procedure. Alternatively, tags can be applied externally or within the stomach of the fish, i.e. an intragastric tag. Each tag emits a unique frequency and pulse rate (non-coded) or uses coded signals wherein tags emit the same frequency but add an individualised code to their signal.

The tag is composed of a battery, electronics, and a transducer (transforms an electric signal into an acoustic signal), which emits ‘pings’ that the hydrophone locates. The battery is the main component, the size and shape of which is chosen according to the characteristics of the species (size, shape etc.), the age of the individual (juvenile vs adult) and the selected tagging method (Brown et al., 1999; Jepsen et al., 2005). While traditional tags require an antenna, more recently antenna-less tags have been developed. Acoustic omni-directional waves propagate through the water to an immersed receiver at a distance between a few meters and a few kilometres away (Pincock et al., 2010). Depending on the location accuracy needed, several hydrophones can be used to triangulate the fish position. The transmitter size is a key limiting factor to the study duration, since it is directly proportional to the battery life and power of the tag. Lower frequency operating tags (30 - 60 kHz) have more power and a larger detection range but involve a larger transducer which increases the tag size (McMichael et al., 2010). Larger, heavier tags can result in abnormal fish behaviour, and this trade-off must be considered when choosing the optimal equipment for a study. It is recommended that the tag weight does not exceed 2% of the fish’s body weight.

The position of receivers is a crucial part of acoustic telemetry studies, they are often arranged to make a gated or gridded array. Alternatively, they can be acoustically shielded to detect in a specific direction or sector. A gated array can be used to follow migration routes and monitor the speed of fish, and highlight barriers impacting river continuity. By placing receivers at bottlenecks within a river, the overall number of hydrophones used can be reduced. The gridded array has the purpose of examining fine-scale movements, habitat use and fish behaviour (Heupel et al., 2006). Alternatively, several hydrophones with overlapping detection ranges can be placed along a river reach to ensure constant tracking of tagged fish. Where multiple hydrophones are placed along a reach range testing is a crucial operation prior to setup to ensure fish can be detected by at least three hydrophones at any given location (Espinoza et al., 2011). It should be noted that tagging is a stressful procedure for fish and following ethical and legal recommendations, researchers should aim to conduct the minimal level of tagging to achieve the aims of their study.

3. Survey Planning

  • Define the array type, the number and size range of fish to be tagged (determined by the study objectives), the river length to monitor, the accuracy needed and the budget.
  • Choose equipment based on the size of the stream and size of fish, its depth, flow speeds, and the ease of connecting to the power grid.
  • Use stationary ‘reference tags’ to measure system performance and be able to check range detection issues.
  • Ask fishermen about their use of the river to; avoid conflict, design your protocol and know the fish behaviour of the river.
  • Minimise equipment loss by labelling your receiver in case of interactions with boat traffic, and commercial fishing equipment.

4. Advantages

  • Allows understanding of complex patterns of behaviour and migration for extended periods of time in rivers, estuaries or seawater, making it appropriate for migratory fish.
  • Does not require multiple captures of any single fish to collect accurate data.
  • Appropriate for juvenile and adult fish.
  • Fish position can be detected through stationary receivers on the riverbank (with a subaquatic device) or from an anchored buoy equipped with the hydrophone, allowing for manual and/or automatic tracking.
  • Tags can be synchronised with all receivers (to synchronise emitting patterns and clock) before the deployment of the array.
  • Passive tracking is less labour intensive and time consuming than active tracking and can be carried out under any weather conditions.
  • High position accuracy which is essential in the context of monitoring.

5. Disadvantages

  • Fish handling and surgery is an invasive procedure which is stressful for fish and can impact migration by inhibiting natural behaviours.
  • Fish can expel transmitters and receivers can be lost because of interaction with anglers or professional fishermen.
  • Hydrophones can only be placed in the water because the acoustic signal cannot be transmitted to antenna. Tracking cannot be done by aircraft.
  • Tags made by one company may be incompatible with the receivers of another company. However, the European Telemetry Network (ETN) aims to provide tag detection information across a range of tag types and manufacturers.
  • Gas bubbles and turbulence interfere strongly with wave propagation.
  • Maintenance of a passive receiver array can be challenging and time consuming.
  • Large volumes of data require frequent downloading.
  • Storage, handling, and manipulation of data can be difficult (Hartog et al., 2009), requiring a spatial data analyst.
  • Equipment costs can be prohibitive - often limiting number of receivers purchased or fish tagged. Furthermore, the cost of tags can be exorbitant.
  • The use of radio transmitters may be easier in shallow environments.

6. Costs

The cost depends on the river length monitored and the degree of accuracy required in the location of the fish. Therefore, it is a trade-off between the number of tagged fish, the spatial coverage and number of receivers, moorings conception, vessel and labour time. This method is time intensive and requires several people at each step, despite whether the monitoring is active or passive. Conducting acoustic telemetry can cost between tens of thousands to several hundreds of thousands of pounds.

7.Data Analysis

Recent advances in manufacturer software has reduced the need for specialist coding, older systems may require specialist coding skills (for further information see related publication in Further Reading). Data handling and analysis remains the biggest challenge and studies should consider computational power and data storage.

8. Further reading

  1. Bergé, J. (2012) Apport de la télémétrie acoustique pour la compréhension de l’utilisation dynamique des habitats par les poissons dans un grand fleuve aménagé, le Rhône. Available at: http://www.theses.fr/2012LYO10092.
  2. Brown, R. S. et al. (1999) ‘Evidence to Challenge the “2% Rule” for Biotelemetry’, North American Journal of Fisheries Management, 19(3), pp. 867–871. doi: 10.1577/1548-8675(1999)019<0867:etctrf>2.0.co;2.
  3. Capra, H., et al. (2018) ‘Individual movements, home ranges and habitat use by native rheophilic cyprinids and non-native catfish in a large regulated river’, Fisheries Management and Ecology, 25(2), pp. 136–149. doi: 10.1111/fme.12272.
  4. Espinoza, M. et al. (2011) ‘Testing a new acoustic telemetry technique to quantify long-term, fine-scale movements of aquatic animals’, Fisheries Research. Elsevier B.V., 108(2–3), pp. 364–371. doi: 10.1016/j.fishres.2011.01.011.
  5. Hartog, J. R. et al. (2009) ‘Developing Integrated Database Systems for the Management of Electronic Tagging Data’, in An Introduction to Fish Migration, pp. 367–380. doi: 10.1007/978-1-4020-9640-2_22.
  6. Heupel, M. R., et al. (2006) ‘Automated acoustic tracking of aquatic animals: Scales, design and deployment of listening station arrays’, Marine and Freshwater Research, 57(1), p. 113. doi: 10.1071/MF05091.
  7. Jepsen, N. et al. (2005) ‘A brief discussion on the 2% tag/bodymass rule of thumb’, Aquatic telemetry: advances and applications. Proceedings of the Fifth Conference on Fish Telemetry held in Europe, (June 2003), p. 295.
  8. McMichael, G. A. et al. (2010) ‘The Juvenile Salmon Acoustic Telemetry System: A New Tool’, Fisheries, 35(1), pp. 9–22. doi: 10.1577/1548-8446-35.1.9.
  9. Pincock, D. et al. (2010) ‘Acoustic Telemetry for studying migration movements of small fish in rivers and the ocean - current capabilities and future possibilities’, PNAMP Special Publication: Tagging, Telemetry, and Marking Measures for Monitoring Fish Populations, (January), pp. 105–118.
  10. Thorstad, E. B. et al. (2013) ‘The Use of Electronic Tags in Fish Research - An Overview of Fish Telemetry Methods’, Turkish Journal of Fisheries and Aquatic Sciences, 13(January), pp. 881–896. doi: 10.4194/1303-2712-v13.