Eyed-Egg to Emergence Survival of Captive-Reared Versus Natural Spring Chinook Salmon in the East Fork Salmon River, Idaho

This study was designed to test for differences in survival from the eyed egg stage to fry emergence for progeny from captive-reared versus natural origin Chinook salmon spawned naturally in the East Fork Salmon River. Using modified hydraulic sampling methods, eyed eggs were inserted back into their natal redd after being enumerated and carefully placed into an egg capsule. Embryo development was monitored through water temperatures and emergence timing was estimated based on existing data. When emergence was predicted, capsules were extracted from the gravel and hatched fish enumerated. Captive-reared fish and natural fish were each treated as study groups and each redd was treated as a sample unit. During the fall of 2007 – 2009, 1,641 eyed eggs were sampled from redds formed by captive-reared females and 1,630 eyed eggs from redds dug by natural returning females. Eyed-egg to emergence survival were averaged from all redds created by captive-reared fish and natural fish, respectively. Emergence survival of eyed eggs from captive-reared naturally spawning adults averaged 80.1% (+/- 0.06, n=41). Natural origin emergence survival averaged 83.9% (+/- 0.08, n=41). Natural origin progeny demonstrated slightly better survival to emergence than captive-reared progeny. However, captive-reared survival was similar, and the difference in survival was not statistically significant as evidenced by overlapping confidence intervals.