Research shows higher survival of Snake River spring Chinook through Snake and Columbia hydrosystem

July 13, 2006

Survival of juvenile Snake River spring Chinook salmon as they migrate past the eight dams of the lower Snake and Columbia rivers was higher in 2006 — 58 percent from Lower Granite Dam to Bonneville Dam — than it has been since federal research began in 1993, the researchers reported this week to the Council (see report, 820k PDF).

“This record high survival is good news for this species. High survival of juvenile salmon is an important objective of regional recovery efforts,” Council Chair Tom Karier said.

The research, conducted by NOAA Fisheries, shows that survival of juvenile Snake River steelhead in 2006 was lower than for Chinook — 37 percent — but still good in comparison to recent years.

The ongoing research focuses on fish that migrate in the rivers, as opposed to those that are transported downriver in barges. According to the report, there are multiple causes of mortality as the juvenile fish travel downriver from hatcheries, where they are incubated and released, past the dams and on to the Columbia River estuary, where they remain for up to a year before going to the ocean. These include the effects of dam passage, but also predation, natural selection, and, importantly, water temperature. Prolonged exposure to warm water is lethal to salmon and steelhead

The research shows that survival of juvenile salmon and steelhead from Idaho hatcheries to Lower Granite Dam, the first dam they encounter on their journey to the ocean, varies with the distance traveled, with fish traveling the farthest experiencing the highest mortality. Lower Granite is the first of eight dams the fish pass on their way to the ocean. The research shows that fish are surviving that journey better today than in the 1960s when there were only four dams in place. The research concerns only fish that had been implanted with passive integrated transponder (PIT) tags and thus could be recorded by PIT tag detectors.

The research also showed that:

• There appears to be a weak but positive correlation between higher flows and higher survival. This could be because the reduced travel time reduces exposure to predators. Higher flows are also associated with higher turbidity, which makes the fish less visible to predators.
• Water temperature appears to have a larger impact on survival than flow, as survival appears to decrease as the temperature increases.
• Guiding fish over spillways, and particularly through the new removable spillway weirs like those now in place at Lower Granite and Ice Harbor dams and planned for installation at other mainstem dams, could help boost survival even further. But only minor improvements in survival through the four lower Snake River dams are likely because of current river operations and fish-passage improvements that already are in place at the dams.
• Ocean conditions appear to override the benefits of improved fish passage at the dams, as poor ocean feeding conditions in the mid-1990s correlated to poor smolt-to-adult return rates for both Snake River spring Chinook and steelhead during that time.
• More information is needed to improve survival estimates for juvenile Snake River fall Chinook, particularly for those fish that spend their first year in the Snake River reservoirs as opposed to migrating to the ocean immediately after birth.

Contacts:

• , Chair, 509-623-4386 
• , Information Officer, 503-222-5161

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