Retrospective Sampling Strategies Using Video Recordings to Estimate Fish Passage at Fishways

Abstract Reliable estimates of population size are critical for fisheries management and for testing ecological hypotheses but can be expensive and time consuming to obtain. Sampling methodologies have been developed to obviate complete enumeration, but their effectiveness can be limited by logistical constraints. A posteriori sampling from digital video recordings, however, permits the application of otherwise impractical sampling schemes. We evaluated the time savings of estimating total run size by a posteriori sampling of video recordings (assisted by motion detection software) in comparison with on-site counting methods. The evaluation was based on 9 years of complete counts enumerated either on site or by a posteriori counts from video recordings of alewives Alosa pseudoharengus migrating through a fishway in Nova Scotia. We compared results obtained using analytical estimation methods with results from simulation-based methods and found them to be the same for simple random sampling and daily strat...