Tracking seals by satellite

Press, 28 February 1986, Page 10

Tracking seals by satellite

From the London Press Service

A satellite navigation system may help settle long-standing arguments about the impact that seals have on fish stocks. Scientists from the Sea Mammal Research Unit (S.M.R.U.) in Cambridge have tracked a grey seal at sea with the aid of satellites.

Ordinary V.H.F. transmitters have been used to tag seals, but their range is limited to about 20 kilometres, so to follow an animal out to sea requires expensive use of an aircraft.

The new approach involves two satellites in polar orbits — one is about ,830 kilometres above the Earth while the other

is at 870 kilometres. They orbit the Earth in about 101 minutes, looking down on a swath 5000 kilometres across.

For tracking seals, the S.M.R.U. needed a small transmitter that would withstanding the water pressure when the seal dives and also resist any knocks and bumps when the animal is ashore. A British firm produced a device that weighs about 800 grams with a battery life of 35 to 40 days. The first seal got her tag on December 21, 1985. On December 30 two fixes were obtained which put the seal on Scroby Sands, off the east coast of

England, about 140 kilometres south-east of Donna Nook where she was tagged. She stayed there until at least January 11, 1986, but on January 17 new information showed that she had swum about 70 kilometres west into the Wash. The transmitters then began to give out.

Future transmitters will incorporate a switch to save the batteries when the seal is under water. The S.M.R.U. is also planning to incorporate further microprocessors into ■ the transmitter to record such things as heart rate, which will provide some indications of what the seal is doing, and the depths and duration of any dives.