Comparison of Three Instream Incubation Techniques for Coho Salmon

Abstract

As part of a strategy to rear salmonids semi-naturally, three instream incubation techniques were evaluated in 2 successive years in a diversion channel of the Big Qualicum River on Vancouver Island in British Columbia. Fertilized coho salmon (Oncorhynchus kisutch) eggs were (1) placed on screens above a single layer of gravel in fish- and light-tight boxes (shallow matrix), (2) interspersed with cleaned gravel in enclosed areas of existing riffles (deep matrix), and (3) interspersed with gravel in small screen cages (baskets) buried in the center of cleaned areas of the riffles. The shallow-matrix units were the least effective, mortality was extensive, and fry size, stage of development, and efficiency of yolk conversion were all relatively inferior. The basket technique was best in the second year, when mean survival was 68%, fry lengths were the largest, rate of development the fastest, and yolk conversion the most efficient. Performance of the deep-matrix boxes was intermediate in effectiveness. A recommended technique is described and compared with egg-planting techniques in general.