Embryo Survival, Substrate Composition, and Dissolved Oxygen in Redds of Wild Brook Trout

Abstract

Survival of brook trout (Salvelinus fontinalis) embryos and alevins in redds and factors affecting their survival were studied in two undisturbed headwater streams, supporting natural reproduction of brook trout, on Pennsylvania's Allegheny Plateau. Both study streams supported relatively high numbers of trout but average size of trout was small. Estimated population was 6,067 fish/hectare and 58 kg/hectare in one stream and 4,507 fish/hectare and 60 kg/hectare in the other. Redds were often located immediately upstream of a small pool or a buried log. Egg pockets were about 5-10 cm below the gravel surface and were sometimes located in a gap between two large stones. Diameter of wild brook trout eggs averaged 4.6 mm. Mean intragravel dissolved oxygen concentration in 36 redds ranged from 3.7 to 10.5 mg/liter but usually exceeded 6 mg/liter. Intragravel and surface water temperatures were similar. Geometric mean particle size of redds ranged from 0.6-mm coarse sand to 14.2-mm gravel with a grand average of 3.3 mm. Estimates of survival to eyed egg, corrected for decay and loss of dead embryos, ranged from 0 to 100% and averaged 69%. Survival was related directly to mean dissolved oxygen concentration and inversely to substrate particle size. Based on the total number of eyed embryos recovered and the estimated number of eggs deposited in redds, survival to eyed egg was 39%. Emergence success from 10 artificial redds stocked with eyed eggs averaged 34% and ranged from 5 to 92%. Fry began emerging in February but peak emergence was in March and early April. Emergent fry averaged 22.5 mm long and 0.067 g in weight. In both streams, estimated egg deposition was about 53,000 eggs/hectare and an average of 1,593 young-of-the-year/hectare were present. Thus, survival from egg deposition to fall fingerling was approximately 3%. Survival from egg deposition to emergence was estimated to be 23%. Survival in redds was apparently adequate to sustain these brook trout populations at relatively high densities.