Kelt Reconditioning: A Research Project to Enhance Iteroparity in Columbia Basin Steelhead (Oncorhynchus mykiss), 2005 Annual Report.

摘要

Iteroparity, the ability to repeat spawn, is a natural life history strategy that is expressed by some species from the family Salmonidae. Estimated rates of repeat spawning for post-development Columbia River steelhead Oncorhynchus mykiss populations range from 1.6 to 17%. It is expected that currently observed iteroparity rates for wild steelhead in the Basin are severely depressed due to development and operation of the hydropower system and various additional anthropogenic factors. Increasing the current expression of repeat spawning rates using fish culturing methods could be a viable technique to assist the recovery of depressed steelhead populations, and could help reestablish this naturally occurring life history trait. Reconditioning is the process of culturing post-spawned fish (kelts) in a captive environment until they are able to reinitiate feeding, growth, and redevelop mature gonads. Reconditioning techniques were initially developed for Atlantic salmon Salmo salar and sea-trout S. trutta. The recent Endangered Species Act listing of many Columbia River Basin steelhead populations has prompted interest in developing reconditioning methods for wild steelhead populations within the Basin. To test kelt steelhead reconditioning as a potential recovery tool, wild emigrating steelhead kelts were placed into one of four study groups (in river release, direct capture and transport, short-term reconditioning, or long-term reconditioning). Steelhead kelts from the Yakima River were collected at the Chandler Juvenile Monitoring Facility (CJMF, located on the Yakima River at river kilometer 75.6) from 11 March to 23 June 2005. In total, 519 kelts were collected for reconditioning at Prosser Hatchery. Captive specimens represented 15.0% (519 of 3,451) of the entire 2004-2005 Yakima River wild steelhead population, based on fish ladder counts at Prosser Dam. Steelhead kelts were reconditioned in 20-foot circular tanks, and fed freeze-dried krill initially (first 2 months of long-term reconditioning) or for the duration of the experiment. Long-term steelhead kelts also received Moore-Clark pellets to provide essential minerals and nutrients necessary for gonadal redevelopment. Oxytetracycline was administered to all reconditioned fish to boost immune system response following the stress of initial capture. To control parasitic infestations two methods were used: an intubation of Ivermectin{trademark} was administered to control internal parasites (e.g., Salmincola spp). and, a Formalin drip system was administered via drip system for the duration of reconditioning to prevent fungal outbreaks. From the steelhead kelts collected at the CJMF, four experimental groups were established; in-river release, direct transport and release, short-term reconditioning and long-term reconditioning. Short-term kelts were reconditioned for 3 to 5 weeks. Surviving specimens were released on May 13, 2005 and June 30, 2005. Long-term steelhead kelts are currently being held for a 6-9 month period with a scheduled release in late November 2005.