Laserfiche WebLink
<br />Fish population density estimates were calculated from the results o6 the two consecutive <br />passes using the modified Saber-LeCren method (Everhart and Youngs 1981). These equations <br />provide estimated density with a 9596 confidence interval. Multiplying the estimated density of <br />each species (Number per hectare) by the average weight of captured fish of that species results <br />in an estimate of the biomass of fish (kilograms per hectare) in the study section. <br />L Benthic Invertebrates <br />Benthic invertebrates were also sampled from the three sites on Rito Seco c:reek on 16-17 <br />August 1988. Three replicate samples were taken in riffle sections at each site. Three samples <br />have been shown to provide an accurate estimate of benthic density (Canton and Chadwick 1988). <br />Samples were taken with a modified Hess sampler, which encloses 0.1 mZ and has a net mesh of <br />' approximately 700 µm (Canton and Chadwick 1984). Benthic samples were preserved in the field <br />with 9596 ethanol containing Rose Bengal biological stain and returned to the lab. C)rganisms were <br />sorted from the debris, identified and counted. Identifications were made to the lowest practical <br />taxonomic level using available keys. Wet weight biomass was determined using an Ainsworth <br />analytical balance. <br />Analysis of benthic invertebrates included calculation of the Shannon-Weaver (H') diversity <br />index (Weber 1973). This index is often used as a measure of the effects of stress on benthic <br />' invertebrate communities (Weber 1973). In addition, replicate samples provide the within site <br />variability for the application of statistical tests. Statistical analysis was conducted on <br />transformed (loglo) density data. This transformation normalizes the density data, which generally <br />exhibits a clumped distribution (Elliott 1977), and allows use of robust parametric tests. Statistical <br />tests included analysis of variance. <br />Periohvtic Alaae <br />1 Algae growing on the stream bottom (periphytic algae) were sampled quantitatively by <br />scraping a known area of submerged rock surfaces from each of the three sites. CMe sample was <br />taken at each site. Each sample consisted of four rock scrapings of 9.6 cmz for r total area of <br />38.4 cmZ sampled at each site. The periphytic algae collected in each composite were placed in <br />a vial with 59'o formalin and returned to the laboratory. <br />A Sedgewick-Rafter counting cell was used to estimate the density of individual algal <br />taxonomic divisions and the species within each division (except diatoms). Algae other than <br />diatoms were first identified using 200x or 400x magnification. The total number ~f centric and <br />3 <br /> <br />