Feasibility of Fish Passage at Alameda Creek Diversion Dam

7.0 Evaluation of the Biological Benefit of Two Passage Options2. The negative effects of genetic drift and inbreeding are inversely proportional to population size.Thus, avoid managing for small population sizes.3. Management of wild populations should be consistent with the history of their genetic patternsand processes. For example, historically isolated populations should remain isolated unless otherconcerns dictate that gene flow must occur. Gene flow among historically connected populationsshould continue at historical rates, even if that calls for assisted movement of individuals.Sufficient life-history diversity must exist to sustain a population through short-term environmentalperturbations and to provide for long-term evolutionary processes. The metrics and benchmarks forevaluating the diversity of a population should be evaluated over multiple generations and include:1. The proportion of the diversity of a life-history trait or traits that existed historically that aremaintained in the existing population.2. The historic (natural) levels and origins of gene flow and genetic diversity relative to the existingpopulation.3. The degree to which the existing population successfully uses available habitats.4. The resilience of the existing population, and its ability to adapt to environmental fluctuations.Review of the fisheries literature suggests that a minimum of 100 breeding pairs of steelhead wouldensure sufficient genetic diversity for a genetically viable population (Langston and Zemlak, 1998)(see Section 6.2).A rainbow trout population currently exists in the Upper Alameda Creek Sub-Watershed. Despiterecent isolation and some stocking, the genome of the historic steelhead population is expected to befairly well preserved in populations isolated above ACDD. Limited genetic research conducted byNielsen (2003) suggests that this population is closely related to Central California Coast steelheadand is likely composed primarily of the isolated, historic steelhead population. Although isolation ofa small population can result in genetic drift and a reduction in genetic fitness (Campbell et al., 1999),Deiner et al. (2007) report that construction of modern dams does not appear to have isolatedO. mykiss populations for long enough to result in a loss of genetic diversity. The East Bay RegionalPark District reports that private property owners have intermittently planted rainbow trout below theOhlone section of upper Alameda Creek for 50 years prior to 1995 (Leidy et al., 2005), and the originof these trout is unknown. Studies conducted in nearby Santa Clara Valley streams, however, suggestthat stocking has had little effect on the genetic composition of most San Francisco Estuary streamO. mykiss (Garza and Pearse, 2008). While steelhead access to the area has been blocked for manyyears, rainbow trout above ACDD likely retain most of the unique genetic character of nativesteelhead, despite prior stocking of hatchery rainbow trout.Facilitating fish passage could potentially introduce some out-of-basin genetic stocks to upperAlameda Creek. Considering the number of hatchery steelhead produced in the Central Valley, thereis a potential for some fish from the California Central Valley DPS to stray into Alameda Creek.However, maintaining a population of at least 100 breeding pairs of steelhead in the Alameda CreekWatershed should allow for adequate within basin genetic diversity. Meffe and Carroll (1997) reportthat some level of gene flow among connected populations is desirable. Some low level of strayingmay even increase the genetic diversity and fitness of the population. Facilitating gene flow amongO. mykiss isolated above ACDD and other O. mykiss populations in the Alameda Creek Watershed(through the provision of passage at ACDD and elsewhere in the watershed) may have a positiveACDD Passage June 2009 Page 7-3