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This paper presents an acoustic archival tag capable of tracking small marine animals. It is also a technology that can be ported to other platforms, such as the next-generation acoustic and Argo floats as well as gliders. Tracking is achieved by standard RAFOS triangulation using the arrival times of unique sound signals emitted by moored sources. At the core of the tag is a custom microchip that controls all system operations. It incorporates the critical acoustic arrival time detector, a thermal sensor, and a pressure sensor interface. All the electronic components are housed inside a cylindrical hydrophone of 25.4-mm length and 10.7-mm diameter. The collected data are archived in nonvolatile memory chips with a total capacity of 4 Mb, sufficient storage to record position, temperature, and pressure on an hourly basis for 2 years. The tag consumes 4–5 μW in standby mode and between 60 and 90 μW while the sound arrival time detector is in operation. The power is provided by two button cell silver-oxide batteries, which enable an active tag lifetime of approximately 2 years.