Survival, Hatching, and Emergence Success of Atlantic Salmon Eggs Planted in Three Maine Streams

We devised and tested a method to evaluate survival of embryos of Atlantic salmon Salmo salar from fertilization through hatching and emergence from the streambed. This method entailed placing freshly fertilized eggs in nylon net bags filled with gravel and burying the bags in simulated redds within a streambed. Two net bags were used; an inner bag of 1 -cm (stretch) mesh allowed alevins to escape after hatching, and an outer bag of 0.3-cm (stretch) mesh prevented alevins from escaping the redd. Multiple redds were placed in each of three streams and removed periodically during the incubation period to assess survival. At the estimated time of emergence, outer bags from the remaining redds were opened and covered with traps to catch emerging fry. These were checked twice weekly until emergence ended. Survival to hatching ranged from 7 to 61% (mean = 30.7%, N = 12 redd samples) and was consistently higher in one of the streams. Survival to emergence ranged from 2 to 12% (mean = 7%, N = 5). Although survival to hatching, based on the known number of eggs implanted, was lower than previously reported, survival to emergence with our method agreed with published results. A large proportion of the planted eggs died and disintegrated during incubation and were not recovered. lf survival to hatching is calculated on the basis of only the total of live and dead eggs and alevins recovered (not incorporating disintegrated eggs), the values range from 10 to 88% (mean = 46.8%, N = 12) and agree well with literature values. Death and disintegration of eggs may be greater than previously reported, and this loss may have caused some studies to overestimate survival.