Issue 1, March 2005

VR3-Argos Monitoring Receiver Deployed in FADIO Project

FADIO (www.fadio.ird.fr) is a research project funded by the DG Research of the European Union, and is comprised of eight European partners and one American partner. The main objective of this program is to develop new observation instruments to better study the behaviour and abundance of pelagic fish (in particular tuna) around Fish Aggregating Devices (FAD).

Vemco acoustic tags and VR2 Receivers are being used in the project to:

• Record the swimming depths of different individuals of an aggregation (species, size)
• Record the time residency of fish around FADs

Because of factors like the large geographic scale of this project and the desire to collect data over a long period without the expense of boat time to periodically visit receiving sites (drifting buoys can be difficult to reach, especially when they are hundreds of miles away from any harbor), this was an ideal situation for deployment of Vemco's recently introduced VR3 technology (see VR3 datasheet) and in particular the VR3-Argos.

Key features of the Argos version of the VR3 which made it ideal for this kind of situation include:

• Uses the Argos satellite system to economically relay collected data back to the researcher from anywhere in the world
• Data is available via the Internet soon after deployment
• Data compression and programmable transmission schedule keep satellite service cost low
• On-board GPS for accurate positioning and time synchronization
• Up to one year battery life using safe, inexpensive alkaline battery
• RS232 Service Port connects the unit to a PC for configuration and data transfer

February 2005 Deployments
During the February FADIO cruise, three VR3-Argos units were attached to FADs around which tagged fish were released. The diagram taken from the Argos website shows the tracks these units took. If you're curious, Argos ID Number 53548 was a unit that had been activated and was sitting on the deck of the research vessel as it returned to the Seychelles.

The VR3-Argos minimizes data cost by taking advantage of the Argos daily billing policy. It accumulates data internally until it has as much as it can send in one day. This incurs one day's service fee from Argos. After that it remains silent on subsequent days until it once again accumulates enough new data to begin a full day of transmitting.

These deployments demonstrated the viability of the data transmission scheme and the associated compression and data reconstruction methods. These involve a "store by exception" strategy in which a record is created for the arrival time and departure of each tagged fish with a daily histogram added for transmitters with depth tags. As well, instead of the "brute force" method usually used to get data to the Argos Satellite, the VR3 uses a Reed-Solomon error correction scheme to encode the entire dataset to be transmitted in a day.

As expected, data from all units has been received without error. For these deployments, the dataset size was 768 bytes which represents over 50 pinger events - the arrival and departure of a tagged fish each representing one event. Our experience with this deployment suggests that the dataset could be somewhat larger than this and of course it can be significantly larger as one moves away from the equator.

From the excerpt of the recovered data shown here, those familiar with the VR2 and Vemco coded tags will see some similarities and some differences. The header includes a description of the formats used for data records. With this knowledge, one can observe that three R256 tags (42, 45 and 45) and three R4K tags (2701, 2702, 2703) were detected in the time slice included. The sequential nature of the tag IDs is not surprising since fish are caught, tagged and released around the FAD to which the VR3 is attached. Note too that the records labelled 50 contain the precise time of day and location of the VR3 as measured by its internal GPS.

Availability
With successful completion of the VR3-Argos evaluation with the FADIO group, we will be making units available to our customers this spring. These should be of interest to anyone with an application in which remote receivers need to be installed at buoys, riverbanks and similar locations.