Of the estimated 27,000 spring chinook salmon projected to cross Lower Granite Dam this year, only about 2,700 (10 percent) are expected to be naturally produced and the rest will be hatchery fish.
The two- and three-ocean adults will be the progeny of adults that spawned naturally in 1995 (750 adults at Lower Granite Dam) and in 1996 (1,360 adults at Lower Granite Dam).
It is positive that more progeny are expected to return than the parents that produced them, but the number of fish entering Idaho to spawn will still be inadequate to seed available habitat. This year's projected natural spring chinook return is lower than the 1990s average of 3,420 or the 1980s average of 5,960. This year's runsize expectation is tiny compared to the tens of thousands of wild spring chinook that used to return to Idaho in the 1960s.
Biologists attribute to nature the slight improvement in fish return compared to parent runsize. Good runoff conditions helped migration to the ocean, and the ocean returned to a more productive state while these fish were rearing there.
The large disparity between the number of hatchery and natural adults returning relates to the number of smolts leaving the state. For example, in 1998 (the outmigration year for the majority of the adults returning this year), biologists estimated that about 350,600 natural spring chinook smolts arrived at Lower Granite Dam from all of the Snake Basin. In contrast, 2.56 million hatchery smolts arrived at the dam so the natural smolts made up about 12 percent of the outmigration, similar to the composition biologists project in the returning adult run.
For rebuilding and recovery, biologists have estimated that the smolt-to-adult return (SAR) must be in the range of 2-6 percent consistently. Generally, natural chinook SAR to Idaho has been less than 0.5 percent with declining runsize as evidence of the poor smolt-to-adult return. Based on the improved environmental conditions, biologists expect this year's SAR for naturally produced spring chinook to be higher than recent SARs and thus a few more adults will return to spawn and start the cycle again.