A simple activity monitoring radio tag for fish

A radio tag is described which facilitates the long-term monitoring of activity events in fish. The tag is a simple peritoneal implant and thus requires no complicated surgery to deploy. A motion-sensing mercury switch interfaced to a microcontroller is used to modulate pulse rate and thus indicate periods of activity. The tag is being used to study the feeding and activity patterns of pike (Esox lucius L.) where laboratory and field trials have shown the system to be robust, long lasting and reliable.