Physiological studies assist steelhead kelt reconditioning programs in the Columbia River basin: A synthesis

ABSTRACT Every spring, many postspawn steelhead kelts (hereafter, “kelts”) migrate downstream through the Columbia River basin, but few return to spawn again. Here, we synthesize research on the physiology of the postspawn period conducted for a project implementing reconditioning of female kelts as a restoration method. By the kelt stage, lipid stores were depleted, leaving muscle protein as the main energy source. During the ∼10-week recovery period after spawning, heavy mortality occurred, and growth rates were minimal or negative. Survival through this period depended on the ability to maintain osmotic homeostasis and access remaining lipid stores. Plasma levels of estradiol and vitellogenin diverged between consecutive and skip spawning kelts beginning at 20 weeks postspawn, enabling screening of fish for reproductive status prior to release. Consecutive spawners consistently grew faster than skip spawners during the 10 weeks after spawning, suggesting that a positive energy balance during this period promotes ovarian recrudescence. Treatments to control parasites and pathogens were required to maximize survival. Spawn timing was similar between first time spawners and reconditioned kelts. Egg production increased at the second spawning. We found no support for a hypothesized trade-off between reproductive investment in initial vs. future reproduction in reconditioned kelts.