Laserfiche WebLink
4 <br />An analysis of variance (ANOVA) (Zarr 1984) showed no significant difference in the mean <br />number of fish caught per seines between study sites in 2007 (Appendix C). Only one site <br />Overton has a significant difference in the mean number of fish caught per siene in any of the <br />years with a Tukey pairwise comparison showing a significantly larger number of fish caught in <br />2003 than in 1999. Neither 2003 nor 1999 is significantly different from 2005 and 2007 at the <br />Overton Site. When all sites are combined there is no significant difference in number of fish <br />caught between years. While there was no statistically significant difference between sites and <br />only one difference between years there were large differences in the number of fish estimated <br />(Table 2). <br />Fish availability for least tern forage may be examined in two manners one is density of fish in <br />the open water areas where terns forage. However, fish per acre does not estimate the total <br />number of fish within a given reach of river due to varying amounts of open water that is <br />dependent on channel width. Therefore we have calculated both fish per acre of open water and <br />number of fish within the open water area of each study site (Table 3). In 2007 the highest fish <br />densities (Figure 1) occurred at Overton while the highest total number of fish was found at the <br />Alda site(Figure 2). Lexington and the Cottonwood Ranch sites had very low numbers of fish <br />(Table 3). <br />A comparison of fish abundance in open water at sites between 1999, 2003 and 2005 (Figure 7) <br />where data from all sites was pooled showed no significant difference at any individual site. Due <br />to the lack of statistical significance it may be possible to combine all sites and get an average <br />fish per mile estimate (Table 4) that would be a reasonable estimate of total fish in the central <br />Platte River. <br />A total of 33 fish species have been identified in the three years of this study. In 1999, 2003 and <br />2005 there were twenty-six, twenty-six and twenty-four species of fish captured respectively <br />(Table 5). In 2007 there were twenty two species collected. The most notable differences in <br />diversity are not in the presence or absence of species which are rare in the Platte River such as <br />orangespotted sunfish, but in the composition of the most common species. Six species (red <br />shiners, sand shiners, bigmouth shiners, brassy minnow, plains killifish and mosquitofish) in <br />every year made up 75% to over 90% (Figure 8) of all fish caught. However, the proportion that <br />each species contributed in any given year varied greatly. <br />Discussion <br />The objective of this study is to look at fish abundance and thus some measure of forage <br />availability for least terns, not at the microhabitat features or the biology that cause swings in <br />species richness or diversity. All of the six most common species are of an appropriate size for <br />least tern forage fish. All six species also utilize shallow water habitats and thus may be <br />susceptible to tern predation. The estimates of the number of fish in the system vary by 2.5 times <br />with 2007 being the lowest population estimate. However, there is no significant difference in <br />the estimated number of fish between years. The large differences in the actual number of fish <br />caught at the different sites also did not result in statistically different populations. While no <br />conclusions are drawn in this report about the decline or increase in fish populations due to the <br />lack of significance it was obvious to the field personnel that either the fish populations in the