Spring Chinook Runsize Estimate Shows Upswing

Editors: This is intended as background for potential stories on the coming chinook run. We will be sending news releases as warranted in the new year. This backgrounder was prepared by anadromous fisheries biologist Sharon Kiefer in the Fisheries Bureau at Fish and Game, (208)-334-3791. Early season estimates of the upriver spring chinook run at the mouth of the Columbia River project a runsize of 364,600 adults. The primary component of the run is expected to be two-ocean hatchery spring chinook, which were produced by adults spawned in 1997. The component of spring chinook that is estimated to be of Snake River origin is higher than average at 206,700 (57%) adults. Of last year's runsize of 178,600 spring chinook adults at the mouth of the Columbia River, only 29% were projected as Snake River origin. However, a look back to the 1997 spring chinook return shows that year also had a higher than average proportion of Snake River fish in the run. Thus, a strong broodyear is cycling through. Idaho spring chinook hatcheries were full in 1997, producing about 7.29 million smolts and a substantial number of younger fish for release. In contrast, the expected number of spring chinook smolts produced from the 1998 hatchery spawners, which were released in 2000, was only 5.35 million smolts and the 1999 hatchery production was even lower. There are multiple ways to estimate how many of the fish at the mouth of the Columbia River will actually return to Idaho and the rest of the Snake Basin upstream of Lower Granite Dam (located just downstream from Lewiston). Currently, the total spring chinook return estimate ranges from 72,900 to 102,900 adults at Lower Granite Dam. The range will "tighten up" as fish begin to move into the Columbia River this spring. Broken down, the composition of the spring chinook adult return might range from 59,000 to 83,300 hatchery fish and from 13,900 to 19,600 natural fish because only 19% of the return is projected to be naturally produced. For hatchery spring chinook, the most recent high return was 33,800 adults in 2000. For natural spring chinook, the most recent high return was 11,300 adults in 1992. This year's natural return will still be half or less of the number of natural fish that returned to the Snake Basin in the 1970s. The natural component of the run also experienced a higher number of adults in the 1997 return. For example, the 1997 redd count in Marsh Creek drainage, which is a wild chinook tributary to the Middle Fork of the Salmon River, was 62 redds compared to the 1995 redd count, which was zero. However, the average redd count in the Marsh Creek drainage in the 1970s was 198, which had already decreased from an average of 439 redds in the 1960s. The higher number of spawners in this year's return will help salmon populations like those in Marsh Creek, but the numbers will not be high enough nor consistent enough to indicate recovery. The bottom line is that there were more hatchery and naturally-produced smolts in the 1999 outmigration. However, the number of juvenile fish released is only part of the equation. The natural variables of the equation also lined up. Rearing conditions, outmigration conditions during 1999, and ocean conditions all contributed to above average smolt-to-adult survival, resulting in a runsize considerably larger than recent runs. Nature's bounty provides a windfall this year that will help sustain natural populations and provide a surplus for several hatchery populations. The expected surplus of hatchery spring chinook means fisheries. Idaho biologists are looking at last year's spring chinook fisheries in the lower and North Fork Clearwater, the Lochsa, the South Fork Clearwater, and the Little Salmon River as the model for this year's spring chinook fisheries. Biologists are reviewing the option of opening new waters, but there will likely be only limited opportunity to hold new fisheries where impacts on listed, naturally-produced fish will be within acceptable limits. Fish and Game expects to submit paperwork to National Marine Fisheries Service to review fishery proposals this winter, with final approval by the Commission in the spring.