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Archive: The "Treasure" Oil Spill, June 2000

Transmitters & GIS Map

Technical information about the satellite transmitters

Rob Crawford
Marine and Coastal Management
Department of Environmental Affairs and Tourism

Peter, Pamela and Percy are carrying ST-10 PTTs (Platform Transmitter Terminals) supplied by Telonics in Arizona, USA. These instruments measure 10 cm * 4.8 cm * 2 cm and have a mass of 75 g. The mean mass of African Penguins is 2836 g. The mass of the instruments is less than that of a good meal.

PTTs are attached to the penguins using Velcro and epoxy resin. Velcro is glued to feathers on a penguin's back and to the bottom of the PTT. The two pieces of Velcro are then joined together. In marine conditions, the glue lifts after about 40 days, when the Velcro will fall from the penguin's back. If the penguin can be located before this, the instrument can be recovered by removing the top piece of Velcro.

Each PTT is fitted with an antenna, which transmits signals to satellites passing overhead. If no satellite is in the vicinity at the time of the transmission, no signal will be received. Pamela's and Percy's transmitters send out signals at intervals of 60 seconds for 12 hours, and then not at all for the next 12 hours. Peter's transmitter sends out signals for eight hours, and then is off for 24 hours. The PTTs have salt-water switches, which prevents the emission of signals when birds are underwater. This saves battery power so that the instruments will transmit over a longer period.

Satellites need to pick up at least two messages from the same instrument on an overpass to provide a valid location. When at least four messages are obtained the location of the bird can be fixed as accurately as 150 m, but possibly only to the nearest km. Fewer messages result in a less accurate fix.

The satellites store information, and then later on download it to the Argos data collection system in France, after which the positions of birds are accessed on line by technicians at Marine and Coastal Management, who email the data to the Animal Demography Unit, so that the SAPmap can be updated. The information transfer process is done daily, usually in the mornings (SA time).

Prior to Peter, Pamela and Percy, 12 ST-10s had been fitted to obtain information on the foraging grounds of penguins at South Africa's most populous breeding colonies. This information proved useful in determining the likelihood of penguins at Robben and Dassen Islands being oiled during the Treasure oil spill.

 


© S. Macdonald, 2000

A transmitter is being fitten onto the back of Pamela.

Screen-grab showing the actual data points (updated 25 July 2000).