A Computerized Editing System for Video Monitoring of Fish Passage

Abstract

We designed and tested a videotape editing system that selected and removed video frames not containing fish images from source videotapes previously recorded in 24, 48, or 72 h time-lapse modes. The system, based on image-processing software and a personal computer, compressed videotapes of the passage of Pacific salmon Oncorhynchus spp. by 75% (±6.8%). The system reduced the length of tape that had to be reviewed without significantly altering fish counts made from the tapes. Fish counts made from visual review of both the edited and source videotapes were similar (P = 0.925). Using stratified random sampling, we selected and edited a sample of 200 d of recordings made at five different locations. The combined location and time data formed a 1,890-d statistical population of fish passage. This sample of source tapes was stratified post hoc into three different categories of fish-passage densities, measured by the number of fish on every 24 h of recorded tape (<100, 100–400, and >400 fish/d). Source tape compression was inversely related to fish passage density. The editing system processed and compressed source videotape recordings representing 24 h of monitoring at a particular site in approximately 2 h. The system was simple to use and did not require operator attention during the automated editing process. The videotape editing system can make it easier, faster, and less expensive to review videotapes of migratory fish passage and is most useful at locations or during times when relatively few fish will be observed per day.