Biologging

There are several type of electronic devices used to monitor the movements and activity of aquatic animals.

An overview of biologging tools used by marine scientists and presented below.

1) PIT Tags

Passive integrated transponder (PIT) tag is a small radio transponder that contains a specific code, which allows individual fish, as well as amphibians, reptiles, birds and even rocks, to be assigned a unique 10 or 15 digit alphanumeric identification. These tags can be surgically implanted into the body cavity or the dorsal musculature of fish, or injected with syringe implanters. Unlike acoustic tags that actively send out a signal, they are “passive” and do not require a battery. Rather than the tag transmitting a signal, the tag scanner (or reader) sends out a radio frequency and when a tag is within range, it will relay the identification code back to the receiver. The lack of a battery is the greatest advantage of the PIT tag since it allows for the production of much smaller tags that can be used on smaller organisms, which will last the life of the fish. The antenna readers for PIT tags have a restricted read range so the tags have to be close to the reader antenna. PIT systems work well for restricted fish passage areas such as fish ladders and pipes.

PIT tag with its syringe implanters

2) Acoustic telemetry

An acoustic telemetry system consists of two main components: transmitters and receivers.

Transmitters are electronic tags that broadcast a series of “pings” (sound pulses) into the surrounding water. Tags are either surgically implanted or attached externally to a fish of interest so that once released into the wild, a tagged fish can be “heard” by any receiver within range. The range can vary from a few meters to more than a kilometre. The signal typically transmits once every minute or two.

Receivers (i.e. hydrophones) are small, data-logging computers anchored near the bottom of a lake or stream or the ocean that “listen” for tagged aquatic animals. When a signal is identified, the tag’s unique ID code is saved with the date and time. The data from any single receiver provide a record of each visit to that location by a tagged fish. Researchers often deploy many receivers over large regions to understand the movement patterns of tagged animals.

Acoustic telemetry consists of implanting acoustic transmitters into fish, which are then detected by an array of acoustic receivers (i.e. hydrophones) moored at fixed monitoring locations throughout the pass whenever the fish is within range of the receiver.

A set of acoustic transmitters of different sizes and an acoustic receiver with an acoustic receiver on top. A PIT tag is also present on the bottom for comparison.

[Left] An acoustic transmitter is inserted in the peritoneal cavity of a grey reef shark through a mid-ventral incision , before closing the incision with surgical staples and releasing the animal. [Right] A spider crab equiped with an acoustic transmitter is passing within the range of an acoustic receiver (hydrophone)

3) Satellite telemetry

• Archival tags

Popup Archival Transmitting tags (PATs) collect and store temperature, depth and light intensity data as the host animal swims through the ocean. At a pre-programmed date and time, the PAT detaches from its host, floats to the surface and uploads stored data to the Argos satellite array. PATs store large volumes of data in onboard memory and summarise these data for lower-volume transmission to satellites. If PATs are physically recovered then the full record can be downloaded from memory. Because day length changes with latitude, and sunrise and sunset times change with longitude, light level data can be analysed to determine where the host animal travelled between PAT deployment and release. Light-level geolocation works best with animals which move over long distances.

• SPOT tags

Satellite tags are detectable over broad geographic areas and remotely relay information to satellite arrays. These tags utilize radio transmissions, requiring the tag to have contact with air to send data (hence satellite tags must be externally attached). External attachment makes satellite tags prone to damage and premature shedding. For studies of shark movements, Smart Position or Temperature Transmitting Tag (SPOT tags) are commonly attached to the dorsal fin. SPOT tags transmit a signal to the Argos satellite array whenever the dorsal fin breaks the surface of the water. These transmissions resulted in geo-location estimates with location accuracies that range from a few hundred meters to ‘somewhere on planet Earth’.

[Left] PAT tag deployed on a tiger shark (Galeocerdo cuvier). [Right] Fin-mounted SPOT tag attached to the dorsal fin of a tiger shark. (Source: www.himb.hawaii.edu/ReefPredator/Tools.htm.)

4) Camera tags and sensors

To get fine-scale measurements of activity and swimming kinematics, we can deploy CATS (Customized Animal Tracking Solutions, Germany) data-loggers on sharks. Tags can be fitted to the dorsal fin with galvanic links. When the galvanic link dissolve, the package releases from the animal and float to the surface. Embedded VHF (Advanced Telemetry Systems Inc.) and SPOT (Wildlife Computers Inc.) satellite transmitters then enable us to locate and recover the loggers. Sensors include 3D accelerometer, 3D rate-gyro, 3D magnetometer (all recording at 20 Hz), and depth and water temperature (1 Hz). The loggers also includes a HD video camera with recording duration of 4–5 hr. For one shark, the video failed to turn on, while for another the video worked but the diary failed to record. A high-pass filter can be used to separate static and dynamic acceleration, and the product of the three axes can be used to calculate overall dynamic body acceleration (ODBA) as a measure of activity. The tri-axial magnetometer can be used to quantify the ‘pseudo-heading’ of the sharks. The magnetometer can also be used to produce an accurate track of the animal as well as to determine when (and how often) the animals changes direction.

CATS cam deployed on a grey reef shark showing how it socialises in the shark aggregation

Biologging data from grey reef sharks #5 (a) and #6 (b) during switching tides. The shaded area represents the outgoing tide. Sensors include swimming depth (dark red, upper line), overall dynamic body acceleration (ODBA, black) and magnetic heading (blue). Pseudo-heading values switching between 0 and 5 signify changes in direction along the South–North axis. Animal-borne video images from shark #6 show polarized swimming in tight groups during incoming tides (i), shoaling during slack tide (ii) and greater dispersion of the group in turbulent outgoing tides (iii) (from Papastamatiou et al. 2021).

5) Transceivers and proximity loggers

Mobile peer-to-peer technologies, such as animal-borne acoustic telemetry transceivers and proximity loggers offer considerable promise, as they can be used to detect associations as animals range over larger spatial scales. Currently, however, these devices remain rather large, expensive, power hungry, and reliant on the retrieval of the logger for data recovery, tending to result in typically short-term deployments on a small number of large animals.

The CATS cam (see above) is associated with a mobile MiniSUR acoustic receiver that records every tagged individual the shark encounters within 30 m range. Temporal patterns and number of associations for this white shark and its associated social network. (Adapted from Papastamatiou et al. 2022)

6) Wireless Autonomous Real-Time Underwater Acoustic Positioning System

Recent acoustic telemetry positioning systems are able to reconstruct the positions and trajectories of organisms at a scale of a few centimeters to a few meters. However, they present several logistical constraints including receiver maintenance, calibration procedures and limited access to real-time data. To overcome this, we recently developped a novel, easy-to-deploy, energy self-sufficient underwater positioning system based on the time difference of arrival (TDOA) algorithm and the Global System for Mobile (GSM) communication technology, capable of locating tagged marine organisms in real time. Its real-time property can be used to rapidly detect system failure, optimize deployment design, or for ecological or conservation applications.

This high-resolution, affordable real-time acoustic tracking system designed for long-term tracking is completely self-sufficient in terms of energy due to its solar panel. The positioning is based by default on trilateration using the time difference of arrival (TDOA) algorithm. This system was designed to be easily deployed and retrieved by a two-person crew without the need for divers. Due to the real-time analysis of the data and a web supervision interface (mobile, tablet and computer), failure detection is possible from the very beginning (More information in Manicacci et al. 2022).