Monitoring Fish Wheel Catch Using Event‐Triggered Video Technology

Abstract

AbstractIn large, turbid rivers, fish wheels are often used as a live‐capture technique for monitoring migratory fish runs. After capture in the wheel's rotating baskets, fish are lifted out of the water, slid down a chute, collected in a live‐box, and then sampled. To eliminate the handling and holding of fish associated with fish wheel live‐boxes, an event‐triggered video system was developed so that fish were video recorded during capture and then immediately released back into the river. A magnetic switch, connected to an exit door installed in the fish wheel chute, signaled a computer to videotape passing fish. Periods of no fish capture were not recorded. Reliability and accuracy were evaluated over a 3‐year period, 2001–2003. In over 14,000 h of operation and 262,000 recorded fish images, the system failed only once (due to a malfunction of the exit door). Fish counts from the video system were 4% higher than counts from fish wheel live‐boxes, mostly because fish were jumping out of the live‐box before counting began. Compared with continuous time‐lapse recordings, the video system missed 1% of captured fish, mostly small Coregonus spp. that passed under the exit door without activating the switch. Subsequent adjustments to the door and software capture settings eliminated undercounting. The advantages of the switch‐triggered video system over traditional fish wheels with live‐boxes were reduced handling and holding time for captured fish; improved counting accuracy; unattended operation; and lower labor costs. Future developments in image recognition and motion detection software should increase the use of event‐triggered video in fishery science.