Illinois Natural History Survey doing a Fish Count.
Fish are stunned by a small, electrical current generated between the two long poles extending from the front of the boat. They are quickly scooped into the boat, where fish species, weight and length are recorded, then quickly returned to the water. The fish are not killed by this proceedure, but recover quickly and swim away. Fish counts are useful in determining the "health" of a body of water by the size and number of species found.
Photograph by Dr. George Bennett, Illinois Natural History Survey.