Table 1 Summary of the various technologies used for tracking animals in freshwater with a brief summary of strengths, limitations, and common applications
From: Tracking animals in freshwater with electronic tags: past, present and future
Technology | Summary of technology and techniques | Strengths | Limitations | Applications |
|---|---|---|---|---|
Acoustic telemetry; manual tracking | Uses a transducer to convert electrical energy to acoustic energy that is detected by an underwater hydrophone | Deep water (>20Â m) | Hydrophone must be submerged in water | Some applications in FW |
Animals usually tracked by boat using bearings and triangulation | Can provide detailed movement data depending on tracking method and conditions | Ineffective in shallow or turbulent water | Mostly for fish, some use with alligator, FW mammals and elasmobranch | |
Not suitable for transmitters with long pulse interval (time between pulses) | Â | Interference from macrophytes and noise (for example, boats, entrained air) | Â | |
Acoustic telemetry; fixed stations | As above | Can be deployed as gates, grids, or arrays to monitor animal movements for long periods, including under ice | Generates large datasets | Widespread use in FW |
Autonomous or cabled hydrophones and associated loggers store time-stamped data when tagged animals enter reception zone | Multiple stations can provide precise two or three-dimensional tracks of animals | Requires significant post-processing and analytical efforts (can be challenging to recover data with some systems) | Mostly on fish, some use with mammals that move between marine and FW environments | |
| Â | Some systems provide real-time data transmission | Interference from macrophytes and noise (for example, boats, entrained air) | Â | |
Radio telemetry; manual tracking | Emit electromagnetic energy in the radio frequency range (usually in the VHF band between 30 and 300Â MHz) | Shallow water (<10Â m) | Deep water (>15Â m) | Widespread in FW |
Signals detected by antennas (aerial or underwater) and a receiver (some have logging capability) | Low-conductivity (<500 μS/cm) | High conductivity Sensitive to localized interference | Fish and other taxa, especially amphibious species (for example, basking turtles, amphibians, some mammals) | |
Tracking can occur from boat, vehicle, air, foot | Relatively inexpensive | Â | Â | |
Functions in moving water and through ice as well as on land and in air | ||||
Radio telemetry; fixed stations | As above | As above | Antennas visible, thus can attract vandals | Widespread use in FW |
Fixed stations with multiple antennas detect and log tags when in the vicinity of an antenna | Suitable for long-term deployments | Not possible to obtain precise two-dimensional positions (mostly presence or absence in a given location) | Mostly used with fish | |
Most often deployed in riverine systems to detect migration | Â | Sensitive to interference | Â | |
| Â | Â | Effectiveness dependent on local geomorphology and station placement [19] | Â | |
Passive integrated transponder telemetry; manual tracking | Integrated circuit chip and coil antenna that transmits a unique identity code when energized by a low-frequency radio signal (generally 125 to 400Â kHz) | No battery (therefore long life) | Largely limited to shallow and restricted lotic systems owing to small detection range (usually <1Â m) | Widespread use in FW |
Detected using hand-held (usually in a backpack with wand waved in or above water surface while wading or walking on ice) or boat-mounted readers | Small | Multiple tags in the same location can prevent signal transmission | Mostly in small fishes, reptiles, amphibians and invertebrates | |
| Â | Inexpensive | Detection range depends on tag orientation relative to the reader | Â | |
Passive integrated transponder telemetry; fixed stations | As above | No battery (therefore long life) | As above | Widespread use in FW |
Antennas deployed in systems that record the time and unique ID of a given tag detection | Small | Remote stations require power source to function | Mostly for fish | |
A variety of antenna designs, mostly for small lotic systems, fishways or other areas where animals congregate | Inexpensive | Â | Â | |
Low-frequency electromagnetic telemetry | Similar principle as PIT tags, but tags are continually powered | Effective in areas with high noise levels where acoustic and radio may be problematic | Site-specific detection only | Limited use in FW |
Greater detection range on the order of several tens of metres (for example, [20, 21]) | Limited tag life | The few examples use fish in lowland rivers [20] | ||
Combined acoustic radio transmitters | Both acoustic and radio output modules can either transmit simultaneously or, if dynamic, can switch between the two | Works in marine and FW | Large devices | Some use in large diadromous fish species and marine mammals that move between marine and fresh waters |
Switching driven by environmental cues (depth or conductivity) [22] | Works for animals that use a wide range of depths or move into higher conductivity waters | More expensive than either radio or acoustic tags | ||
Archival tags (no transmitting capability) | Biologging tags (for example, data storage tags, time-depth recorders, archival geolocation tags) | Continuous monitoring of desired parameter (for example, temperature, depth) | Require tag recovery to download data from onboard memory | Some use in FW, mostly for logging temperature, depth, geolocation, and other environmental parameters (especially for ectothermic animals) |
Do not transmit data remotely | Occasionally log physiological information (for example, acceleration, heart rate) | |||
Always equipped with some form of sensor | Â | |||
Communicating histogram acoustic transponders and business card tags | Hybrid loggers and transmitters, first logging data to memory and later transmitting data when interrogated by a receiver | Useful for wide-ranging fishes that have low recapture probabilities but return to download sites [23] | Reasonably large | Not applied in FW to our knowledge (mostly marine applications) |
Business card tags are a variant where the logging function actually serves as a mini acoustic receiver and can log other tagged animals that it encounters [24] | Expensive | |||
| Â | Some versions require that tags are retrieved to download data | |||
Smart position-only tag with real-time GPS | Satellite platform transmitter which identifies tag location by real-time uplinks to orbiting Argos satellites whenever tag breaches the water surface (some variants may include archival capability rather than only transmitting in real time) | Real-time positioning | Relatively expensive | Mostly marine |
Provides information on broad-scale movement of animals (for example, ocean basin scale) | Individual must breach water | Some use in large FW animals that surface (for example, alligators, manatees) | ||
Detailed records of environmental conditions experienced | Limited to large animals | Â | ||
Archival pop-up satellite archival transmitter tags | Tags programmed to jettison at a given time or when tags experience a specific event (for example, fail to change depth for a specified period of time) at which time they float to surface and transmit summary data or packets to satellites | Provides information on broad-scale movement of animals (for example, ocean basin scale) | Most release links based on corrosive link, switched on via applied voltage and require sea-water to function | Mostly marine |
Geopositioning commonly based on light levels | Detailed records of environmental conditions experienced | Limited to large animals | Most FW applications involve diadromous animals tagged during FW phase with pop-off scheduled for when they are in marine systems | |
Can also log depth and temperature | Â | Relatively expensive | Exception: studies on FW porpoises [25] | |
| Â | Â | Tags and downloading technology not always reliable, needs further refinement | Â |