Electronic juvenile salmon at Bonneville dam in the US are helping scientists determine the impact of turbines on fish as they migrate downstream towards the ocean.

The fish, known as sensor fish were developed by the Pacific Northwest National Laboratory (PNNL) scientists. Microsensors in the sensor fish measure and store information about the forces a real fish would feel. ‘The sensor fish was invented to deal with the difficulty of understanding conditions fish face when travelling through operating hydro turbines,’ said Tom Carlson, PNNL sensor fish project manager. ‘There are hydraulic conditions, turbulence and shear that generate high forces on fish.’

PNNL began testing the sensor fish in December 1999. Forty-five days of study began when the first sensor fish was dropped into an old Kaplan turbine at Bonneville dam and a second was dropped into the recently installed minimum gap runner turbine (MGR). The MGR is designed to reduce the gaps at the turbine and around the runners that catch or pinch some juvenile fish travelling through the turbine. (See IWP&DC April 1999, p42).

During the test the sensor fish were supposed to surface in the dam’s tailrace, but the first two were not recovered. It is thought that the balloons attached to the fish, which are designed to inflate after going through the turbines, failed.

Fish developed since this first experiment have been retrieved successfully and PNNL scientists are now back-calibrating the data they obtained which will be compiled with future data. According to Carlson, the measurements taken with the sensor fish are a small part of tests currently going on at Bonneville dam using 120 live juvenile salmon per day.

The sensor fish is 5cm wide, 15cm long and weighs about 175g. The mould that covers the electronics is made from an impression of an actual smolt, but only has an anal fin. The skin is impermeable and flexes just as the body of a juvenile fish might when in a turbine. It has an internal power supply, an analogue to digital converter and a communications port. One fish costs about US$5000 — 50% of this is due to the instrumentation and 50% is the cost of assembly.