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.
Trapping facilities are regularly used to achieve a variety of fishery research and management goals. Though care of sampled organisms is a central tenet of most agencies, the effects of trapping on fish behavior are seldom quantified. We used passive integrated transponder technology to calculate passage delay and blockage of adult Sockeye Salmon at a facility where all spring‐migrating fishes were trapped for research between 2008 and 2010. Median passage delay ranged from 0.4 to 8.7 days, and 8% to 38% of the return (2,387 to 21,090 adults) was precluded from reaching upriver spawning habitat. A protocol limiting trapping to less than 24 h per week was implemented in 2011 and median delay decreased to 6 min, with the result being that nearly all fish were able to ascend to spawning grounds for two consecutive years. The annual variation in delay was unrelated to run size or river flow, indicating that research activities requiring intensive trapping operations had inadvertently blocked tens of thousands of adult salmon from reaching spawning tributaries. We use this case study to advocate the adoption of a precautionary approach where trapping of adult migratory fishes is proposed but the effects are unknown.
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