A fish activity-monitoring device using a low-power infrared photobeam

An activity-monitor system for fish or other aquatic animals has been developed that uses a single low-level infrared (IRED) photobeam. The IRED source emits with a peak wavelength of 960 nm and requires only 70-mW average power input for an operating range of greater than 50 cm in sea water. This represents an order of magnitude reduction in power and more than a doubling of range over other reported designs. The cost for a single-beam channel is approximately $30.