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The Problem
The Santa Ana sucker (Catostomus santaanae), was recently identified by the U.S. Fish and Wildlife Service (FWS) as a species of special concern. This sucker is endemic to the Los Angeles, San Gabriel, and Santa Ana river drainages of southern California. Although commonly found in these river drainages during the 1970s, only the San Gabriel River population is now believed to be viable and self-sustaining. An introduced population occurs in the Santa Clara River, but it has apparently hybridized with another introduced sucker. In response to evidence of declining populations, the U.S. Fish and Wildlife Service (FWS) was petitioned by the Sierra Club Legal Defense Fund, Inc., to list the Santa Ana sucker as an endangered species. The petition and supporting documents were reviewed by FWS and determined to be sufficient to warrant further consideration for listing. During the status review of this species, FWS will need information on environmental limiting factors that affect abundance and distribution of the Santa Ana sucker. This subtask will identify the physicochemical variables that are most strongly associated with variations in population density. Without such information, conclusions from the FWS status review of this species will be couched in greater uncertainty. The Santa Ana sucker, a member of the sucker family (Catostomidae), is a relatively small fish that rarely exceeds 200 mm standard length. Sexual maturity is attained during the second summer of life (age I+), and adult fish usually die at the end of their third summer. However, a few individuals may live through a fourth summer (age III+). The streams in which the Santa Ana sucker is found are subject to periodic, severe flooding that result in drastic decreases in sucker densities. However, adaptations such as short generation time (early maturity), high fecundity, and a relatively long spawning season (spring through early summer) enable the sucker to rapidly repopulate streams following floods. Deteriorating environmental conditions associated with urbanization, water diversions, dams, pollution, heavy recreational use, gold mining wastes (suction dredging), gravel extraction, and introduced competitors and predators are suspected of contributing to the decline in abundance and distribution of Santa Ana sucker populations. Although some information is available on status and possible threats facing sucker populations in the Los Angeles River, the San Gabriel River, and the Santa Ana River, the specific factors responsible for decline of Santa Ana sucker populations are unknown. This project is funded under RA# 98-304 between the National Fish & Wildlife Foundation and BRD. Objectives The 5-year research goals of the Fisheries and Aquatic Resources Program are to understand relationships between and among aquatic species habitats and provide science for restoring and maintaining declining species and their required habitat. The purpose of this subtask is to develop a better understanding of natural and anthropogenic factors responsible for decline of the Santa Ana sucker. Specifically, this subtask will attempt to identify the physicochemical variables that are most strongly associated with variations in population densities of this sucker. Results from this subtask will enable FWS biologists to better establish a scientifically defensible link between the decline of sucker populations and deteriorating environmental conditions. Data collected by this subtask will also provide a realistic baseline for designing future laboratory tests that estimate the tolerance thresholds of the Santa Ana sucker to selected environmental stressors. Methodology 1. Sampling reaches. Two replicate sampling reaches were established on selected streams in the Los Angeles basin that historically supported or currently support endemic populations of the Santa Ana sucker. Study streams included the Santa Ana River and the San Gabriel River. 2. Sampling times. All reaches were sampled at quarterly intervals during December 1998-December 1999.
3. Fish collections. Santa Ana suckers were sampled with a battery-powered backpack electroshocker. Immediately after collection, Santa Ana suckers were hand-sorted from the catch and retained alive in buckets of water for additional processing. All other fish were identified, counted, and promptly released. Santa Ana suckers were measured (standard length) and examined for evidence of breeding tubercles (reproductive males develop tubercles over most of the body but are most dense on the caudal and anal fins and the caudal peduncle, whereas reproductive females possess tubercles only on the caudal fin and the peduncle), then returned unharmed to the water. When unidentifiable species of fish were encountered, voucher specimens were preserved in 10% buffered formalin for later identification with taxonomic keys. 4. Water quality and quantity measurements. Hydrolab DataSonde multiprobe loggers (Hydrolab Corporation, Austin, TX) were used to measure the following water quality variables continuously at 15-min intervals from near the bottom at a fixed station located at the upstream boundary of each sampling reach: water temperature, dissolved oxygen concentration, pH, specific conductance, ammonia, and turbidity. Standard methods were used to make all water quality measurements. In addition, stream discharge was roughly estimated by measuring current velocity and water depth at intervals along a cross-sectional profile of the stream channel. Color photographs were taken at each sampling reach to supplement written descriptions of salient habitat features.
5. Environmental contaminant measurements. During September 1999, samples of Santa Ana suckers (whole fish) were collected in triplicate from each sampling reach and preserved with methods recommended by chemists from the BRD Columbia Environmental Research Center. Samples were air freighted to two FWS-approved contract laboratories for exploratory analysis of heavy metals and persistent organic compounds. 6. Statistical analysis. Raw data were stored as Lotus 1-2-3 files (Lotus Development Corporation, Cambridge, MA) and summarized with SAS (SAS Institute Inc., Cary, NC) and other statistical and graphical software. Multivariate statistical procedures were used to identify environmental variables that best explain variations in population densities of the Santa Ana sucker. Unless indicated otherwise, the probability of type 1 error for all statistical tests will be specified as a=0.05. Highlights and Key Findings The purpose of this subtask was to develop a better understanding of environmental factors responsible for the decline of the Santa Ana sucker by determining if population attributes of this species at sites where it is currently abundant, common, and rare or absent varied in relation to selected environmental variables. Seasonal (once every three months) electrofishing surveys began in December 1998 and terminated in December 1999 at one site on the East Fork of the San Gabriel River (SGR) and two sites on the Santa Ana River (near the Metropolitan Water Districts pipeline in Riverside County, MWD; and at the Imperial Highway bridge in Orange County, IMP). A total of 7,307 fish was collected from the three sites, of which 715 were Santa Ana suckers. Santa Ana suckers were captured only at SGR (average, 6.6 fish/10-min electrofishing) and MWD (average, 2.3 fish/10-min electrofishing). Analysis of length frequency distributions indicated that three distinct size classes occurred at SGR whereas only one or two distinct size classes occurred at MWD. These observations suggest that substantial numbers of suckers in their third year of life were present at SGR whereas few suckers lived beyond their second year of life at MWD. Evidence of recruitment (presence of 21-30 mm juveniles, the smallest standard length category measured during this study) was first detected in June at MWD and in September at SGR. These findings, along with observations of breeding tubercles in suckers during March and June at SGR but only during March at MWD, suggest that reproduction occurs earlier in the year at MWD than at SGR. Standard lengths attained by presumably young-of-the-year suckers in December averaged 36-48 mm at SGR and 63-65 mm at MWD. Comparison of relative weights indicated that, on average, body condition was higher among suckers from SGR than from MWD. Although gut contents of suckers from both sites in September 1999 consisted almost entirely of organic detritus (a mixture of unrecognizable plant material) and sand, animal foods (aquatic insects and other invertebrates) were slightly more important in fish from SGR (2.4-2.5%, damp-dry weight basis) than from MWD (0.8%). Body burdens of selected environmental contaminants (organochlorines and trace elements) measured in suckers from SGR and MWD were not elevated beyond average concentrations reported in freshwater fishes from throughout the United States. Relative abundance of Santa Ana suckers was inversely correlated with specific conductance and stream discharge, and directly correlated with relative abundance of Santa Ana speckled dace (Rhinichthys osculus) and rainbow trout (Oncorhynchus mykiss). However, results from multiple regression analysis indicated that the abundances of arroyo chub (Gila orcutti) and rainbow trout, the only independent variables retained by the statistical model, accounted for nearly 89% of the variation in Santa Ana sucker abundance. Where Are We Headed In 2003 A final report for this work has been completed. In FY-03, we will attempt to draft a technical manuscript for submission to a professional journal. Project Contact Michael Saiki Email: michael_saiki@usgs.gov Publications |
