New Salmon Doubling Index Displays Telling Trends in Chinook Salmon Populations
Posted November 12, 2012
(Click graph to enlarge)
Salmon Index Blog Series
The 20th anniversary of the Central Valley Project Improvement Act came on October 30, 2012. In recognition of this milestone, it is timely to take a step back and consider our progress towards achieving the Act’s goals. This multipurpose federal water legislation mandated changes in management of the Central Valley Project, particularly for the protection, restoration and enhancement of fish and wildlife. To that end, the CVPIA established the Anadromous Fish Restoration Project (AFRP) with the directive to “implement a program which makes all reasonable efforts to ensure that, by the year 2002, natural production of anadromous fish in Central Valley rivers and streams will be sustainable, on a long term basis, at levels not less than twice the average levels attained during the period of 1967-1991.” This goal is also a state legal requirement, adopted by the State Water Resources Control Board.
NRDC and the Golden Gate Salmon Association today released a Salmon Doubling Index designed to summarize the progress that’s been made toward achieving that doubling goal. This index does not provide new data. Rather, our goal is to develop a tool that highlights the trends presented in, but sometimes obscured by, the complexity and annual fluctuations of existing data.
This post summarizes some of the most important information revealed by this analysis, and explains the methodology used to generate the index.
This new index measures overall progress in restoring salmon runs by: (1) including a three-year running average that reflects the three-year lifecycle of Chinook salmon, and (2) measuring progress as a percentage of the population doubling mandate established in the CVPIA and in similar requirements under state law. Per state and federal requirements, this index excludes hatchery fish. Hatcheries are important to the fishing industry; however, wild fish are a better indicator of ecosystem health. In addition, healthy wild runs are the best way to ensure a sustainable salmon fishery in the long-term.
The following facts, drawn from our analysis, highlight the magnitude of the recent Chinook salmon population crash and its correlation with water diversions:
- In 2002, the index peaked at 64.33% of the salmon doubling goal. The 2002 index includes the last cohort of adult fish to have hatched and traveled through the Delta as vulnerable juveniles prior to the pumping increases that helped to drive the ecosystem and salmon crash that bottomed out with record low populations in 2009. (The three-year Salmon Doubling Index hit an all time low in 2010.)
- Between 1994 and 2002, natural production averaged 15% higher than the doubling goal’s baseline period; the CVPIA was progressing towards its salmon doubling goal, and the population was rebounding from its 1992 crash.
- Between 2000 and 2006, freshwater pumping from the Sacramento-San Joaquin River Delta increased 20% in comparison to the period from 1975-2000.
- Beginning in 2003, Chinook salmon entered a precipitous decline through 2009. In 2010 the three-year running average reached 7.41% of the salmon doubling goal.
- In 2009, natural production was estimated at 41,516 adult fish.
- Prior to this most recent population crash, the lowest annual natural production on record was still nearly five times the size of the 2009 population.
- In 2008, a federal court established stronger protections for salmon, reducing freshwater diversion from the Delta and setting the stage for a modest rebound.
- Three years later, in 2011, we see fish populations rebound modestly, resulting in an index that’s 13.25% of the doubling goal.
The impacts of modifications to in-stream salmon habitat are typically seen three years later, corresponding with the life cycle of Chinook salmon. Young Chinook salmon travel downstream to estuaries and ultimately the ocean, where they feed and then return to their original streams three years later to spawn. Once the three-year life cycle is taken into account, this index reveals a strong correlation between increased – and decreased - freshwater diversions and population fluctuations.
The crash from 2003 to 2009 was unprecedented, and while the 2012 season will likely show continued improvement, Central Valley Chinook are still recovering. When rebounding populations are put in the context of the doubling goal, it’s clear that we still have a long way to go to establish sustainable healthy Central Valley salmon fisheries. As my colleague Barry Nelson points out in his blog, there are various factors, in addition to flows, that drive salmon population fluctuations. However, to quote Barry, “It’s not that healthy flows are the only thing salmon need. It’s that they can’t survive without them.”
This new Salmon Doubling Index is based on the methodology and data used by the Department of the Interior in establishing its 990,000 fish doubling goal. This effort began by using estimates of yearly natural production and in-river escapement for all races of adult Chinook salmon calculated in the most recent CHINOOKPROD (a spreadsheet maintained by the AFRP). CHINOOKPROD estimates yearly natural production for all races of adult Chinook salmon in Central Valley rivers and streams. This source provided data through 2010. Natural production estimates were then calculated for the year 2011 by applying conversion factors used in earlier years.
We used this data to calculate three-year running averages of natural production totals for all races of Chinook salmon in the Central Valley system. This averaging period reflects the three-year life cycle of Chinook salmon. By averaging natural production in three-year increments, the aim is to provide a snapshot regarding the status of the last three Chinook “year classes” and to smooth the noise caused by year-to-year natural variability. The resulting averages were then divided by the annual production target for all races combined (990,000) to calculate the percentage of the CVPIA salmon doubling goal met over that three-year period.
More information about how this index was created can be found here, in a Salmon Doubling Index methodology memorandum.