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High Chinook Jack Count After 2001 Drought

by Bill Rudolph
NW Fishletter, June 27, 2002

The 3,900 jacks that have returned to the Snake River this year are sending a strong signal that last year's drought may have had little effect on the 2001 juvenile spring chinook migration from Idaho. That's the gist of a NMFS internal memo sent from agency scientists in Seattle to the agency's Portland-based hydro operations division last month.

Since most of last year's migration was barged from lower Snake dams to the estuary, some NMFS scientists had already speculated that damage to runs from the drought and low flows might not be nearly as catastrophic as some had predicted. In fact, the jacks, precocious males that return home a year earlier than most of the run, are returning at a slightly higher rate this year, as of June 30, than they did in 2000, when flows and spill regimes were fairly normal during their outmigration. Even before they reached the first dam, the fish survived amazingly well in the low flow year of 2001.

Bill Muir, a scientist at the National Marine Fisheries Service, told the Power Planning Council last winter that adult returns might not be as bad as predicted because most of the spring chinook and steelhead had been barged through the hydro system. But even before they reached the first dam the fish survived amazingly well in the low-flow year of 2001, he said. Muir told the council that survival of hatchery fish averaged about 60 percent to Lower Granite, the first dam on the lower Snake, which was about 10 percent higher than survival rates during the gully-washer year of 1997. In 2000, an average water year, survival averaged about 70 percent from the hatcheries to the dam.

NMFS' June 24 memo mentioned that earlier presentation to the council. "At that time," it said, "we stated that despite the poor migration conditions, the strength of the subsequent adult run would likely hinge mostly on conditions downstream from Bonneville Dam and in the ocean."

Fish managers had publicly agonized over what they called an impending fish disaster in the spring of 2001 from the low flows caused by the drought and little snowmelt. ODFW's Christine Mallette told The Seattle Times last April that smolts were "swimming backwards" and losing their sense of direction because of the slow-moving water. In the end, most found their way to the dam and a free ride downstream.

Idaho fish managers supported the maximized barging strategy, but other state agency and tribal managers wanted more water from Idaho to boost flows--water that irrigators weren't willing to part with.

Snake River Spring-Summer Chinook Jack Return Counts Other managers called last year's migrants "the death brood" because of poor conditions in the river and near ocean environment, where the drought had produced a freshwater plume of paltry proportions--a situation that most scientists thought would increase mortality, since the young fish generally like to hang out in the plume. The fish typically thrive there because it is a region of concentrated nutrients and its water, turbid with river sediments, offers protection from predators. But less than 10 percent of the Snake River spring chinook and steelhead were still in the mainstem beyond the three lower Snake dams where fish were barged, and only about 26 percent of that number made it below Bonneville Dam.

"This was one-fifth lower than the estimated 33 percent average survival for hydropower system migrants during the 1993 and 1994 outmigrations," said the NMFS memo, "prior to the implementation of BiOp spill, and approximately one-half of the estimated 50-percent survival for hydropower system migrants during the 1995 through 2000 outmigrations."

Until the numbers of returning jacks were analyzed last month, fish managers had speculated that poor conditions in the estuary and plume might decimate the run. But the sizable spring chinook jack return rate (figured as a percentage of total spring and summer chinook released from Snake Basin hatcheries the previous year) has raised eyebrows. "Based on these data," the memo says, "we expect that the complete adult return rate from the 2001 outmigration will likely fall in the range of those from the last few years."

Further, the memo goes on to explain that the adult spring and summer return to the Snake in 2001 was the largest on record, with this year's return taking second place. The memo pointed out that those returns resulted primarily from large hatchery releases (nearly 11 million smolts in 1999 and 7 million smolts in 2000). The scientists said they expect considerably fewer adult fish to return next year, since the hatchery release that gave them their start only amounted to 4.1 million fish.

Nevertheless, the high jack return rate continues a trend that took a dramatic jump in 1998, when returns climbed to six times the rates of the early 1990s, when ocean conditions were less productive. In 1999 and 2000 returns continued upward to a rate more than 10 times that of the early 1990s. A graph that accompanied the memo showed a dip in the returning jack rate in 2001 to about seven times that of the early 1990s, but it has shot back up this year to about 12 times the survival rate of the early 1990s. It is actually a bit better than the previous high for the 2000 jack return--a group of fish that found estuary conditions and an ocean plume generated from average spring flows, not the dismal local conditions facing last year's migrants, when flows from the Columbia River were about half of normal and the second-worst on record.

The hydro BiOp includes language to study the importance of the plume, which has been under way for several years now. Preliminary evidence suggests that the plume may play a more important role in the survival of fall chinook and coho migrants than for spring chinook.

Harvest managers saw coho jacks plummet last year, a fact they attribute largely to low survival in the small 2001 ocean plume (Coho jacks return only a few months after they migrate to sea). WDFW's Doug Milward said early indications from the ongoing coastal sport fishery show more than a five-to-one ratio of chinook to coho, which he said may bear out their reduced expectations for coho abundance this year. "By now, coho should be flooding Ilwaco and other areas," said Milward. "I've never seen it like this and I've been doing it for 12 years."

Bill Rudolph
High Chinook Jack Count After 2001 Drought
NW Fishletter, July 19, 2002

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