Reproductive Performance and Energy Balance in Consecutive and Skip Repeat Spawning Female Steelhead Reconditioned in Captivity
Steelhead Oncorhynchus mykiss are known for their life history diversity, displaying a range of freshwater residence ages, maturation ages, and spawning intervals. Female maturation is thought to be condition dependent at critical periods, during which individuals falling below energetic thresholds remain reproductively inactive for the subsequent annual cycle. After their initial, or maiden, spawning, females may enter into another maturation cycle and spawn after 1 year (consecutive spawners) or 2 years (skip spawners). The purpose of this study was to quantify reproductive performance in maiden, consecutive, and skip spawning female steelhead, which differ in their energy availability schedules during ovarian development, in order to quantify the benefits that can be expected from kelt reconditioning programs. Hatchery origin female steelhead returning to Dworshak National Fish Hatchery for their maiden spawning (Clearwater River, Idaho, 2013–2016) were manually spawned, placed in tanks, and reconditioned. Size (somatic mass, FL) and reproductive performance (total, individual, and dry egg mass, fecundity, and fertilization success) were measured, and spawn date fidelity was determined. Repeat spawners had greater mass, length, and mass at length than did maiden spawners. In absolute terms, skip spawners had greater total, individual, and dry egg mass than maiden and consecutive spawners, and both consecutive and skip spawners had greater fecundity than did maiden spawners. When standardized for size, skip spawners had greater total, individual, and dry egg mass than maiden and consecutive spawners; size-standardized consecutive spawners had lower individual egg mass than maiden spawners but higher fecundity. Our results suggest that egg size and reproductive investment are determined early in oogenesis based on an assessment of energy reserves, and do not increase when excess energy is available during the vitellogenic period of oogenesis. Instead, excess energy during the vitellogenic period is allocated to somatic growth. Increases in fecundity and egg size suggest that reconditioned kelts released to spawn naturally will be more productive than maiden spawners.
Jenkins, L.E., A.L. Pierce, N. Graham, R. Branstetter, D.R. Hatch, and J.J. Nagler. 2018. Reproductive performance and energy balance in consecutive and skip repeat spawning female steelhead reconditioned in captivity. Tran. Amer. Fish. 147(5): 959-971. Online at https://doi.org/10.1002/tafs.10089.