Effectiveness and Trade‐Offs Associated with Hydraulic Egg Collections from Natural Salmon and Steelhead Redds for Conservation Hatchery Programs

Abstract

AbstractMaintaining a large genetically effective number of breeders (Nb) in supplemented salmon populations is considered vital to their long‐term sustainability, yet may be difficult to consistently achieve in practice, especially in conservation hatchery programs that require small numbers of eggs for captive rearing. We evaluated efforts to hydraulically collect eggs from naturally produced redds, as implemented by conservation hatchery programs for Endangered Species Act listed populations of Snake River Chinook salmon Oncorhynchus tshawytscha and Hood Canal steelhead O. mykiss; we then compared the estimated Nb represented in the hydraulically collected captive populations with the Nb obtained by the more conventional approach (i.e., adult collection and artificial spawning). Egg collection goals in the steelhead and Chinook salmon conservation hatchery programs were met in most cases and were never exceeded. The embryo viability and egg‐to‐fry survival consistently exceeded 90% and were no less than would be expected through artificial spawning. Demographic estimates suggested that a greater Nb in the captive population would be obtained by hydraulic redd sampling than by artificial spawning of captured adults to produce a specific, limited number of eggs. Hydraulic redd sampling allows sexual selection to occur naturally on the spawning grounds and does not require barrier weirs, handling of adults, or the removal of a female's entire fecundity from natural production. The high rate of survival to emergence for hydraulically collected eggs (>95%) suggests that eggs are not damaged by the collection process, but the fate of uncollected eggs that are disturbed during the process is unknown. Hydraulic redd sampling requires fairly frequent redd surveys to time collections at the proper stage of embryonic development, and access to some redds in remote areas can be difficult. Hydraulic sampling of eyed eggs appears to have largely accomplished the goals of these small‐ to moderately‐sized conservation hatchery programs.