Estimation of Pacific Salmon Escapement with a Time‐lapse Video Recording Technique
A time‐lapse video system was designed and used to record the migration of adult Pacific salmon at Tumwater Dam on the Wenatchee River, Washington. From 1989 through 1991, the system was evaluated to determine its suitability and usefulness for escapement estimation of three Pacific salmon species, Chinook Salmon Oncorhynchus tshawytscha, Sockeye Salmon O. nerka, and steelhead O. mykiss. The accuracy and precision of estimates based on these videotape records were tested. Video‐based sockeye salmon escapement estimates were found to be within 4% of an independent estimate based on the on‐site visual counts made by experienced observers. An among‐observer variance test was performed comparing the counts of five different individuals who examined the same videotape records. Analysis of variance showed no significant differences among the five observers. A test that compared the effect on counts of different time‐lapse recording speeds indicated no significant differences between the two speeds tested, 48‐h and 72‐h modes. The amount of nighttime fish passage, measured between 2000 and 0400 hours, was estimated and averaged for each species over the three study years. Mean values ranged from 6.68 to 16.24%, which indicated that a significant portion of salmon migration at Tumwater Dam occurred at night. An additional test that compared these observations with those of a study of nighttime salmon passage at mainstem Columbia River dams suggested that the ratio of nighttime passage to that of the previous day was similar among study sites. The videotape system appeared to be a useful method for estimating Pacific salmon escapement, which offered several important advantages over on‐site counting. These advantages include improved accuracy, a permanent record of migration, and cost efficiencies that are particularly noteworthy in areas of low escapement. Also, a video record of salmon migration can be used to calculate bounded escapement estimates, and individual specimen identification can be confirmed. The tape analysis process of counting and identifying fish can be automated by means of a computerized image‐processing system.
Hatch, D.R., M. Schwartzberg, and P.R. Mundy. 1994. Estimation of Pacific salmon escapement with a time‐lapse video recording technique. North American Journal of Fisheries Management 14(3):626-635. Online at https://doi.org/10.1577/1548-8675(1994)014<0626:EOPSEW>2.3.CO;2.