Relative Reproductive Success of Reintroduced Hood River Spring Chinook

Supplementing declining salmonid populations with hatchery-reared individuals is an important fishery management tool used to increase abundance for conservation and/or harvest objectives.  Integrating locally-derived natural origin individuals into supplementation broodstock can help offset negative effects on fitness such as inbreeding and domestication selection.  However, when entire populations have been extirpated from historically occupied areas, no indigenous stock remains to initiate a re-introduction program, necessitating use of an out-of-basin stock.  We examine how a reintroduced stock in the Hood River, Oregon, may be adapting to its new environment, as reflected by differences in reproductive success between hatchery and natural origin individuals.  Spring-run (stream-type) Chinook salmon were deemed extirpated from the Hood River basin following seven consecutive years (1965-1971) of essentially zero escapement to the fish ladder at Powerdale Dam.  A re-introduction program was initiated in 1986 with annual releases of juveniles from Carson NFH, then beginning in 1993 with releases from the adjacent Deschutes River stock.  To create a localized Hood River stock, an increasing proportion of in-basin adult returns have been incorporated into the hatchery broodstock. Here we report results, involving genotyping of ~7,700 individuals across 18 years (1992-2009) using 15 microsatellite loci, followed by parentage analysis for hatchery and natural origin individuals spawning above Powerdale Dam (brood years 1992-2004).  Our results showed that fish returning to the Hood River during this period were mixtures of the reintroduced stream-type genetic lineage as well as an unexpected proportion of stray fish from the Lower Columbia lineage.  The stream-type and Lower Columbia lineages are evolutionarily distinct in the Columbia River Basin, and their sympatry in the Hood River affords a rare opportunity to study their relative reproductive success, in addition to comparisons between the hatchery and natural origin fish derived from the Carson then Deschutes supplementation stocks.