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Ocean Conditions, Lack Of Biodiversity Likely Caused Sacramento River Chinook Collapse
Columbia Basin Bulletin March 20, 2009
"What caused the Sacramento River fall Chinook stock collapse?"
Recent years' severe dropoff in adult returns was likely the result of an inhospitable ocean pushing a chronically vulnerable fish population nearly off the edge, according to a report/analysis released this week by NOAA Fisheries Service's Southwest Region.
"The evidence pointed to ocean conditions as the proximate cause because conditions in freshwater were not unusual, and a measure of abundance at the entrance to the estuary showed that, up until that point, these broods were at or near normal levels of abundance," according to the report, whose title appears in quote above. "At some time and place between this point and recruitment to the fishery at age two, unusually large fractions of these broods perished."
"The long-standing and ongoing degradation of freshwater and estuarine habitats and the subsequent heavy reliance on hatchery production were also likely contributors to the collapse of the stock," the report says. Those factors have effectively made the outmigrating juvenile fish less fit, less diverse genetically.
"The situation is analogous to managing a financial portfolio: a well-diversified portfolio will be buffeted less by fluctuating market conditions than one concentrated on just a few stocks; the SRFC seems to be quite concentrated indeed."
"In conclusion, the development of the Sacramento-San Joaquin watershed has greatly simplified and truncated the once-diverse habitats that historically supported a highly diverse assemblage of populations," the report says. "The life history diversity of this historical assemblage would have buffered the overall abundance of Chinook salmon in the Central Valley under varying climate conditions.
"We are now left with a fishery that is supported largely by four hatcheries that produce mostly fall Chinook salmon. Because the survival of fall Chinook salmon hatchery release groups is highly correlated among nearby hatcheries, and highly variable among years, we can expect to see more booms and busts in this fishery in the future in response to variation in the ocean environment."
The report was prepared at the request of the Pacific Fisheries Management Council, which asked that NOAA Fisheries' southwest and northwest fisheries science centers form a multi-agency task force to research about 50 potential causes of the decline in Sacramento fall chinook salmon returns.
The full report can be found at http://swr.nmfs.noaa.gov/Default.htm
The task force was made up of scientists from the centers, the PFMC staff, the U.S. Fish and Wildlife Service, Oregon, Washington and California fishery management agencies, the University of Washington, the University of California-Davis and Humboldt State University.
Sacramento River fall chinook returns to the river dipped to an estimated 88,000 adults in 2007, which was below the PFMC's escapement conservation goal of 122,000-180,000 for the first time since the early 1990s. Last year's return to hatcheries and natural spawning areas was even smaller, 66,000 spawners.
Forecasts of a poor Sacramento return, and the poor status of many west coast coho salmon populations, forced the PFMC last year to adopt the most restrictive salmon fisheries in the history off the West Coast of the United States. The regulations included a complete closure of commercial and recreational chinook salmon fisheries south of Cape Falcon, located near Nehelem on the central Oregon coasts.
The negative economic impact of the closure was so drastic that western governors asked for $290 million in federal disaster relief funding. Congress appropriated $170 million.
Escapement from 2001-2006 ranged from a high of 775,000 in 2002 to 268,000 adult spawners in 2006. The forecast for 2009 is 122,000, which would be slightly above the PFMC's conservation standards.
The chinook have typically fueled huge ocean sport and commercial fisheries and still allowed large escapement. Those fisheries averaged more than 800,000 chinook caught per year from 2000 to 2005, according to the PFMC.
The PFMC is one of eight regional fishery management councils established by the Magnuson Fishery Conservation and Management Act of 1976 for the purpose of managing fisheries 3-200 miles offshore of the United States' coastline. The Pacific council recommends management measures for fisheries off the coasts of California, Oregon and Washington.
According to the report, the review was limited to potential causes for the decline for which there are reliable data to evaluate. The research team analyzed the performance of the 2004, 2005 and 2006 broods of Sacramento River fall chinook and looked for corresponding conditions and events in their freshwater, estuarine and marine environments.
The report discusses the impact of long-term degradation in freshwater and estuarine habitats and the effects of hatchery practices on the biodiversity of chinook in northern California's Central Valley, and how reduced biodiversity may be making chinook fisheries more susceptible to variations in ocean and terrestrial climate.
The naturally spawning chinook return to the spawning grounds in the fall and lay their eggs in the low elevation areas of the Sacramento River and its tributaries. The resulting young fish migrate into the estuary in May and June.
Most of the fall chinook hatchery production from four state hatcheries is trucked to the estuary, where some smolts usually are acclimatized briefly in net pens and others released directly into the estuary.
"A broad body of evidence suggests that anomalous conditions in the coastal ocean in 2005 and 2006 resulted in unusually poor survival of the 2004 and 2005 broods of SRFC," according to the March 18 "pre-publication" report to the PFMC. The council will discuss the report findings when it meets April 2-9 in Millbrae, Calif., to shape, among other things, its recommendations for ocean fisheries this summer.
"Both broods entered the ocean during periods of weak upwelling, warm sea surface temperatures, and low densities of prey items. Individuals from the 2004 brood sampled in the Gulf of the Farallones were in poor physical condition, indicating that feeding conditions were poor in the spring of 2005 (unfortunately, comparable data do not exist for the 2005 brood)," according to the report.
The report says there is little the PFMC can do directly to improve the situation but it can support efforts that would lead to increased diversity of the Sacramento fall chinook and increase population stability.
"Mid-term solutions include continued advocacy for more fish-friendly water management and the examination of hatchery practices to improve the survival of hatchery releases while reducing adverse interactions with natural fish.
"In the longer-term, increased habitat quantity, quality, and diversity, and modified hatchery practices could allow life history diversity to increase in SRFC. Increased diversity in SRFC life histories should lead to increased stability and resilience in a dynamic, changing environment," the report says.
"Using an ecosystem based management and ecological risk assessment framework to engage the many agencies and stakeholder groups with interests in the ecosystems supporting SRFC would aid implementation of these solutions."
Page Updated: Thursday May 07, 2009 09:14 AM Pacific
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