Recent Habitat Studies
December 2014, Stoecker Ecological: Habitat Quality, Rainbow Trout Occurrence, and Steelhead Recovery Potential Upstream of Searsville Dam
This Report confirms many of the findings of Stanford's 1996 assessment of the Corte Madera floodplain (see below), and expands upon previous surveys in the upper watershed.
- With dozens of high-quality photographs of riparian habitat areas in the upper watershed, this report focuses on o.mykiss habitat available in tributaries upstream of Stanford's Searsville Dam.
- The overwhelming conclusion of years of field surveys, study, observations, and photo documentation is that steelhead would recover miles of quality stream habitat in the upper watershed if Searsville Dam is removed.
June 2013, Stanford Technical Study / Summary of existing information: URS: Existing Biological Conditions
- The study area for this summary of existing information includes those areas most likely to be affected by the potential future actions being considered by Stanford for Searsville Dam and reservoir, which are assumed to include Searsville Reservoir, marshes and wetlands upstream of Searsville Reservoir (to upstream limit of areas of sediment deposition or directly influenced by Searsville Reservoir and Dam), and Corte Madera and SF creeks downstream from Searsville Dam to San Francisco Bay.
- Due to high residence time of water in the reservoir, associated decreases in water quality and increases in temperature, and the presumed abundance of predatory, nonnative fishes, Searsville Reservoir may not be a very hospitable environment for native fishes.
- Native fishes may colonize the reservoir from upstream, but the reservoir itself may be a sink for most native fishes, where predation is heavy, thermal stress common, and reproduction low or nonexistent.
Steelhead and rainbow trout are the same species and the term steelhead may refer to resident rainbow trout that co-occur with steelhead.
SF Creek below Searsville Dam (including tributaries Bear Creek and Los Trancos Creek) is included in Santa Clara Hydrologic Unit 2205 of designated critical habitat for CCC steelhead (50 CFR 52488-52627).
SF Creek supports one of the few remaining steelhead runs in tributary streams to San Francisco Bay. Figure 6.2 [reproduced at right] illustrates the number of steelhead per mile collected from various reaches of Corte Madera Creek downstream of Searsville Dam, SF Creek and Los Trancos Creek between 1997 and 2006. The main limiting factors for steelhead production in the SF Creek watershed are availability of winter refuge (from high flows) habitat, high summer water temperatures, and impediments to passage.
Steelhead are known to spawn within the SF Creek watershed including some portions downstream of Searsville Dam that flow through Stanford University property (Stanford University 2012).
August 2007, Center for Ecosystem Management and Restoration: San Francisco Estuary Watersheds Evaluation Identifying Promising Locations for Steelhead Restoration in Tributaries of the San Francisco Estuary
Eight of our region’s watersheds account for about 75 percent (i.e., 175 stream miles) of the regional habitat resources, and we call these “anchor watersheds” to reflect their importance.
October 1996, Stanford University, Center for Conservation Biology and Department of Biological Sciences: Biotic assessment of upper Searsville Lake and the lower floodplain of Corte Madera Creek
- In the area that is now the highly modified reservoir and floodplain of the Searsville Lake/Family Farm Road study area, original native species likely included steelhead/rainbow trout (Oncorhynchus mykiss) [...] and coho salmon (Oncorhynchus kisutch). In recent years, however, the only native species that have been observed with any regularity in the study area are Sacramento sucker and rainbow trout.
- In spite of the general lack of native fishes, the nearly complete physical alteration of the drainage in the study area, and the large numbers of non-native species inhabiting Searsville Lake, the area cannot be ignored in terms of conservation planning. Of particular interest for conservation planning are rainbow trout (Oncorhynchus mykiss). This species is protected by numerous conservation and game laws and the steelhead form is being considered for federal protection at the present time[.]
- The presence of rainbow trout/steelhead in the study area or downstream from the study area definitely impacts landuse decisions. The presence of non-native species of centrarchid fishes (sunfish, blackbass, and crappie) is also an important consideration for conservation planning. These fishes are detrimental to virtually all native aquatic organisms and any landuse decisions should be evaluated in terms of their impact on non-native fishes.
- Several of these species, most notably largemouth bass and brown bullhead, are significant predators on other fishes (and anything else they can swallow) and are impacting the biotic communities present in the area -- undoubtedly to the extent that bass are a major factor in structuring the aquatic community present in Searsville Lake.
- Full PDF available here.
UC-Davis Center for Watershed Sciences Research
October 2014: Assessing Flows for Fish Below Dams: A Systematic Approach to Evaluate Compliance with California Fish and Game Code 5937
The UC Davis Center for Watershed Sciences & U.S. Geological Survey (USGS) identifies Searsville Dam as one of California's "problem" dams "in most need of attention to protect fish, particularly native species."
Despite California Department of Fish and Wildlife Code 5937, which requires dam operators to release enough water downstream to keep fish in good health, Stanford does not have flow release measures at Searsville Dam to protect threatened steelhead and other sensitive species downstream.
This study offers a systematic framework for identifying dams that likely need improved downstream fish flows as required under Section 5937. From an original pool of more than 1,400 dams, 220 are identified as high-priority candidates for further investigation of environmental flow needs for fish. These dams fall within a broad range of biogeographic settings and represent a wide diversity in size, function and ownership.
Related coverage in the California Aggie: Breakthrough study to ensure fish safety under water dams
100 years of California’s water rights system: patterns, trends and uncertainty, Environmental Resource Letters (2014).
The state has allocated a total maximum allowable use of 370 million acre-feet of surface water -- more than five times the 70 million acre-feet available in a year of good precipitation, according to the researchers' review of active water rights on record.
Related news coverage: California’s flawed water system can’t track usage. Associated Press, May 27, 2014.
Related report at KQED Science: How California’s Water Rights Make It Tough to Manage Drought (December, 2014)
"It doesn’t necessarily amount to a fair system or an efficient system." — Buzz Thompson, Stanford University
Salmon and other native freshwater fish in California will likely become extinct within the next century due to climate change if current trends continue, ceding their habitats to non-native fish, predicts a study by scientists from the Center for Watershed Sciences at the University of California, Davis.
The study assessed how vulnerable each freshwater species in California is to climate change and estimated the likelihood that those species would become extinct in 100 years.
The researchers found that, of 121 native fish species, 82 percent are likely to be driven to extinction or very low numbers as climate change speeds the decline of already depleted populations. In contrast, only 19 percent of the 50 non-native fish species in the state face a similar risk of extinction.
More information at http://news.ucdavis.edu/search/news_detail.lasso?id=10617 / PDF report at http://www.plosone.org/article/fetchObject.action?uri=info:doi/10.1371/journal.pone.0063883&representation=PDF
California's native populations of Pacific Coast salmon and trout appear to be rapidly headed toward extinction.
Eighty-one percent of anadromous taxa are threatened with extinction and 73% inland taxa are either threatened or already extinct.
[M]ajor causes of decline are related to increasing competition with humans for water, human degradation of watersheds, and adverse effects of hatchery propagation. Climate change, interacting with the other causes of decline, is increasing the trajectory towards extinction for most populations.
Other Studies on Reservoirs and Climate Change
Several recent studies have found that dams and reservoirs are a major source of methane emissions worldwide. New research shows that reservoirs in temperate areas can emit as much as tropical reservoirs, and that sediments trapped behind reservoirs are a significant factor. Stanford's sediment-choked Searsville Reservoir is particularly susceptible to elevated methane emissions due to high erosion rates upstream and nutrient input from adjacent horse facilities and upstream agricultural lands leased from Stanford.
November 2014, United Nations, Intergovernmental Panel on Climate Change: 5th Assessment Report.
The most recent UN Climate Change Report identifies the habitat impact from dams and reservoirs as an environmental concern in need of climate change mitigation actions. The report states with "high confidence" that species extinctions will be driven by several climate-associated drivers including reduced river flows and interaction with eutrophication and invasive species.
Stanford University's operations at Searsville Dam currently results in reducing and/or eliminating downstream flows. The reservoir enables ongoing eutrophication and proliferation of invasive species that spread downstream.
More at http://www.ipcc.ch
October 2014, Climate Central: Dams & Reservoirs May Be Huge Source of Methane Emissions
Globally, reservoirs could emit up to 104 teragrams of methane per year. By comparison, NASA estimates that global methane emissions associated with burning fossil fuels totals between 80 and 120 teragrams annually.
Another 2014 study found that midlatitude dams and reservoirs are a globally significant source of methane. The highest rates of methane emissions occur at in shallow reservoir areas and where sediment deltas are created at reservoir tributaries. Agricultural nutrient input and high sediment loads are identified as major contributors to high methane production in reservoirs. More at http://pubs.acs.org/doi/pdf/10.1021/es501871g
June 2013, Environmental Science and Technology: Sediment Trapped by Dams Creates Methane Emission Hot Spots
Inland waters transport and transform substantial amounts of carbon and account for ∼18% of global methane emissions.
There are millions of small dams worldwide that receive and trap high loads of organic carbon and can therefore potentially emit significant amounts of methane to the atmosphere. This report evaluated the effect of damming on methane emissions in a central European impounded river.
The reservoir reaches are the major source of methane emissions and emission rates far exceed previous estimates for temperate reservoirs.
Our results suggest that sedimentation-driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7%.
August 2012, Science Daily: Methane emissions jump dramatically during dam drawdowns
Researchers have documented an underappreciated suite of players in global warming: dams, the water reservoirs behind them, and surges of greenhouse gases as water levels go up and down. In separate studies, methane levels jumped 20- and 36-fold during drawdowns.
Historical Habitat Surveys & Reports
1906, David Starr Jordan, First President of Stanford University: The Trout and Salmon of the Pacific Coast
This historical fisheries report from Stanford University's first president documents trout species native to Stanford campus, and features excellent illustrations of fish including the steelhead illustrations to the right and a Rainbow trout: sea-run specimen from San Francisquito Creek below.
In 1898, David Starr Jordan said: Our treatment of animals will someday be considered barbarous. There cannot be perfect civilisation until man realises that the rights of every living creature are as sacred as his own.
1905, John Otterbein Snyder, Stanford University Assistant Professor of Zoology, Report to the Bureau of Fisheries Management: Notes on the Fishes of the streams flowing into San Francisco Bay, California
Large PDF report also available here