Use of Direct Observational Techniques to Assess the Effects of Flow on White Sturgeon Egg Predation

Flow conditions in a White Sturgeon (Acipenser transmontanus) spawning area in British Columbia, Canada will be affected by the Waneta hydroelectric expansion development.  To address concerns that reduced velocities under some flow conditions in a portion of the spawning area had the potential to result in increased predation on developing sturgeon eggs, the proponent committed to an egg predation study. We used a combination of two direct observational techniques; an underwater time-lapse camera mounted over a filter-fiber egg collection mat (MatCam) and DIDSON sonar imagery. The DIDSON documented hourly densities of potential large-bodied egg predators and provided data suitable for statistical examination of flow-fish density relationships. The photos from the MatCam allowed species identification and also documented the presence of small-bodied predators not detectable by the DIDSON. In addition, we “seeded” the mat of the MatCam with fertilized sturgeon eggs to determine egg predation rates and identify predator species. We present the findings of the first three years of the seven year program and describe how unexpected behavioural interactions among fish species and towards the sampling gear strongly affected species and density observations and confounded interpretations of possible flow-predator relationships.