Laserfiche WebLink
Because the razorback suckers that were available for the July and August marking tests <br />were hatched in late April, they were much older and lazger than the razorback sucker larvae that <br />were unsuccessfully marked in May 2005. Therefore, we used those lazger and older razorback <br />suckers as well as 8-d-old fathead minnows (about 6 to 7 mm TL). Those fathead minnows were <br />similaz in age to the razorback suckers mazked in May but were smaller than the May razorback <br />suckers. Thus, if younger age or smaller-sized fish have higher toxicity to the ALC solution, that <br />should be apparent from the fathead marking tests, assuming similar tolerance of ALC by the two <br />species at young life stages. <br />Tests showed high survival of razorback suckers and fathead minnows in ARL, Ouray, <br />and reference water conditions on each marking date (Table 1). The younger and smaller fathead <br />minnows had slightly lower survival compared to razorback suckers but survival rates of each <br />species in treatment and reference conditions was similar on each date. This suggested that <br />toxicity due to effects of ALC in Ouray Hatchery well water was not a likely source of mortality <br />for the fish that died during mazking in May. <br />A possible confounding factor in August marking tests is that lazge amounts of hard water <br />elements precipitated out of solution in the hard water used in those experiments. We stirred that <br />water prior to testing to ensure that some of the precipitate was included in test water but it did <br />not re-dissolve. It is unknown if precipitation could have removed the toxic elements before they <br />could interact with the ALC solution. The only means to assess this would be to conduct <br />mazking tests with the water immediately after it is drawn. However, it is likely that the water <br />used for fish marking also had some time to precipitate hazd water elements before the May <br />mazking was conducted. A chemist or water quality expert with experience in hazd water <br />chemistry interactions may also be able to give some insight into whether small amounts of KOH <br />could interact to produce toxic effects with constituents present in the hard well water at Ouray. <br />Future mazking should be conducted with. the less hard well source if possible to reduce the <br />chances of creating toxic marking solutions. Test marking a few fish with marking solutions for <br />up to an hour prior to immersing lazge batches of fish should also be part of the marking <br />protocol. <br />Page -3- <br />