Effects of Captive Reconditioning and Post-spawning Life History on Reproductive Performance in Female Steelhead (Oncorhynchus mykiss) Kelts
Post-spawn female steelhead (kelt) reconditioning is a recovery tool addressing endangered populations in the Snake River. Wild kelts are captured, fed, and released to travel upstream and spawn naturally without returning to ocean a second time. Kelt reconditioning capitalizes on iteroparity, the ability to repeat spawn, and the natural selection that occurred prior to initial spawning. Reconditioned kelts may re-mature to spawn in one year (consecutive spawner) or in two years (skip spawner). Rematuring females can be identified by elevated plasma estradiol levels 6-9 months prior to spawning. Quantifying the benefit of kelt reconditioning requires comparing the reproductive performance of consecutive and skip spawning kelts to that of maiden spawners. Dworshak National Fish Hatchery origin steelhead, a model for native Clearwater River B-run steelhead, were spawned and reconditioned upon return to the Hatchery to serve as a research tool. Females were air-spawned upon return to the hatchery. Reproductive prformance was assessed. Eggs were fertilized in vitro and fecundity was assessed by weight. Reproductive development and growth were tracked via serial sampling. Reproductive performance was assessed at second spawning for kelts. Results to date were analyzed by comparing spawning categories. 23% of surviving kelts spawned after one year of reconditioning. 100% of remaining kelts spawned the following year as skip spawners. Total egg weight and fecundity increased to a greater extent with increasing length in kelts than in maidens. Egg size and fecundity were greater in kelts than in maidens. Fertilization success was reduced in skip spawners. Consecutive spawners increased in weight more rapidly and tended to accumulate more muscle lipids than skip spawners during the first 6 months after reconditioning. Growth rate and muscle lipids levels decreased during the 6 months prior to spawning in both consecutive and skip spawning kelts.
Jenkins, L., A. Pierce, S. Everett, N. Graham, L. Medeiros, R. Branstetter, D. Hatch, and J. Nagler. 2015. Effects of captive reconditioning and post-spawning life history on reproductive performance in female steelhead (Oncorhynchus mykiss) kelts. American Fisheries Society Annual Conference, August 16-20, 2015. Portland, OR.