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Notes:
So how can such a large geographic area produce such few fish? Drastic declines ocurred for several reasons: 1.) In the late 1800s and early 1900s unscreened diversion dams resulted in high rates of entrainment into irrigated fields in nearly all the upper yakima tibutaries. Also, between 1939 and 1989 operations at Roza dam either prevented or delayed most steelhead bound for the upper yakima. A new fish ladder was installed in 1989 and enumeration at the facility for adult steelhead began in 1992. Since 1992, Upper yakima steelhead returns have ranged from 14 to 236 with an average of 92 adults. Biologist have hypothesized the likelihood colonization and increased production of the resident ecotype throughout vacant portions of the upper yakima during the extended period of minimal anadromous production. Biologists have speculated that the resident O. mykiss that had remained above the site contributed to the rapid recolonization during periods of low anadromous production (Berg 2001).