In Situ Freezing as a Cause of Mortality in Brown Trout Eggs

Abstract

Abstract In November 1975, 60 Vibert boxes, each containing 100 green eggs of brown trout (Salmo trutta), were placed in artificial redds in the Laramie River in southeastern Wyoming. Water depths and, velocities were measured, and a representative substrate sample was collected at each site. Because of extensive ice cover in March 1976, only 20 of the 60 boxes of eggs were recovered. Survival of eggs in these boxes was low (average, less than 1%), and only 10 of the 20 boxes contained live eggs (survival range, 0.5 to 3.4%; average, 1.95%). Three boxes were completely frozen, even though they were buried 15 cm in the substrate and covered with 12 to 20 cm of flowing water. Eleven of the 20 redds, including two of the frozen sites, fell within established spawning criteria for brown trout (water depth, 9 cm or more; water velocity, 15-46 cm/s). No correlation was demonstrated between water depth and survival (r = 0.51) or between water velocity and survival (r = -0.21). Extremely low water temperature and...