A Digital Acoustic Tag, or DTAG, is a specialized miniature recording device designed for temporary attachment to marine animals. Its primary function is capturing detailed information about an animal’s movements and the sounds it produces or encounters in its underwater environment. This technology allows researchers to observe complex marine life behaviors without direct visual contact. DTAGs are a non-invasive tool, providing unique insights into species challenging to study in the wild.
Core Components of a DTAG
A DTAG system integrates several components for data collection. It includes a suite of sensors, such as accelerometers, measuring body movement and orientation, and magnetometers, providing heading data. Pressure sensors continuously track depth, revealing detailed dive profiles, while hydrophones capture the animal’s vocalizations and ambient sounds in its surroundings.
These sensors are connected to a data logger and recorder, which stores collected information, often using solid-state memory. A rechargeable battery powers the system for continuous underwater operation. The tag is encased in a polyurethane hull, often with syntactic foam flotation to ensure resurfacing after detachment. Attachment to the animal is achieved with four silicone rubber suction cups for temporary, non-harmful adherence.
How DTAGs Capture Animal Behavior
DTAGs operate by continuously collecting data from their sensors at high sampling rates. Accelerometer data, sampled at 50 Hz, provides information on the animal’s three-dimensional body orientation, allowing researchers to discern subtle movements like fluke strokes. Pressure sensor data continuously charts the animal’s depth, creating precise dive profiles that reveal patterns of ascent, descent, and time spent at various depths.
Hydrophones, sampling audio at rates from 48 kHz to 192 kHz, record both the sounds made by the tagged animal and ambient sounds, including those from other animals or human activities. This synchronous recording of audio and sensor data allows for precise correlation between an animal’s movements and its acoustic interactions. All data points are recorded and stored on the tag’s internal memory, providing a comprehensive, autonomous record of behavior during deployment.
Scientific Discoveries Enabled by DTAGs
DTAGs have advanced the study of marine animal behavior, revealing unknown aspects of their lives. For instance, data from DTAGs has uncovered the intricate foraging strategies of deep-diving species, such as beaked whales, demonstrating their ability to undertake dives exceeding 1,800 meters in search of prey. This technology has also shed light on complex social interactions and communication patterns among cetaceans, allowing analysis of vocalizations in context with physical movements.
Beyond natural behaviors, DTAGs have been used to assess energetic costs of movements like swimming and diving, by correlating activity levels with energy expenditure models. DTAG data has also provided significant insights into marine animals’ responses to human-made sounds, including naval sonar and shipping noise, by precisely documenting behavioral changes like altered dive patterns or cessation of foraging in response to these disturbances. These findings contribute to conservation efforts by identifying specific impacts of human activities on marine ecosystems.
Deploying DTAGs in the Wild
Deploying DTAGs in marine environments involves a planned deployment and retrieval process. For larger marine animals like whales, DTAGs are attached using suction cups mounted on a long pole, or sometimes with a crossbow. This method allows researchers to place the tag without direct handling, minimizing disturbance.
To ensure animal welfare, DTAGs are designed for a limited attachment duration, typically a few hours to a day. The tag detaches automatically through a timed release mechanism, often involving a corroding wire or by venting the suction cups. Once detached, the tag is buoyant due to syntactic foam flotation and floats to the surface, emitting a VHF radio signal to aid retrieval for data offload. Successful deployment and recovery of DTAGs require specialized skills and careful coordination in challenging marine conditions.