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The Problem
The Department of Interior may play a prominent role in removing Matilija Dam in the Ventura River system, California and wishes to use this subtask as a case study to develop information and conceptual frameworks for planning the removal of other dams and predicting the physical and biological consequences. The primary biological goal for removal of Matilija Dam is to allow steelhead (the anadromous form of Oncorhynchus mykiss) access to approximately 30 km of nearly pristine habitat above the dam, while causing no irreparable harm to native biological communities lower in the river system. If fully funded, this study will address four issues that are important to the evaluation or success of dam removal: (i) interannual variability in production of resident rainbow trout (O. mykiss) or steelhead both above and below Matilija Dam and habitat requirements of southern steelhead; (ii) ancestry and population structure of resident rainbow trout above Matilija Dam; (iii) interrelations between resident rainbow trout and steelhead; and (iv) production dynamics and habitat utilization for tidewater goby (Eucyclogobius newberryi). Under current funding, the study addresses only (ii) and (iii). Objectives The 5-year research goals of the Fisheries and Aquatic Resources Program addressed are to: understand relationships between and among aquatic species habitats; provide science for restoring and maintaining declining species and their required habitat; and investigate aquatic species diversity. Specific objectives are to (1) validate the utility of otolith microchemistry for determining the proportions of O. mykiss in the Ventura River from an anadromous (i.e., steelhead) mother or a resident mother; and (2) characterize the population structure (hatchery vs. native ancestry) of resident rainbow trout upstream from Matilija Dam. Methodology Sagittal otoliths are ground and polished to reveal the primordia and assayed with a wavelength dispersive microprobe to determine Sr/Ca along a transect from the primordia to the edge of the otolith. Genetic population structure is determined from haplotype and allele frequencies for mtDNA and DNA microsatellites, respectively. Highlights and Key Findings 4/19/2002 - Participated in various meetings to define the scope for projects related to removal of Matilija dam. Conducted spawning surveys for O. mykiss below Matilija dam. Evaluated otolith microchemistry (Sr/Ca ratios) for studying rainbow-steelhead interactions in the Ventura River system and determined that high natural levels of strontium in the river system preclude the use of this valuable tool. The final sample for genetic analysis was collected during March 2002 and the samples sent to the Alaska Science Center where they will be assayed. The funding for this project has ended. A final report is in preparation.
9/1/2001 - Fifty rainbow trout have been sampled by electrofishing in each of six tributaries or reaches above barriers in the Ventura River system for molecular genetic analysis. These samples have been shipped to Alaska Science Center for analysis, and will be supplemented with one additional sample. Scales were taken from each of the 300 fish, and age determination is almost complete. A small number of the trout were sacrificed and their otoliths assayed for Sr/Ca. This ratio can be an extremely powerful tool for investigating steelhead-rainbow trout relations; however, we found that high Sr/Ca in the primordia of fish from the Ventura system negates the tool's utility in this drainage. Reconnaisance surveys identified one steelhead redd and a number of rainbow trout redds in the spring of 2001. Full implementation of this study depends on supplemental funding from BOR or other sources, and has not yet materialized. Where Are We Headed In 2003 Complete genetic analyses. Prepare a final report for the genetic and otolith analyses. Project Contact Reg Reisenbichler Email: reg_reisenbichler@usgs.gov Publications |
