Laserfiche WebLink
<br />001754 <br /> <br />31 <br /> <br />· assess native/non-native fish interaction by conducting diet and incidence of <br />predation studies on non-native fishes (primarily rainbow and brown trout), and <br />. reduce the abundance of non-native fishes in the control reach as much as practicable. <br />Examination of the preliminary results from 2003 and winter 2004 indicate that the <br />January, February, and March of2003 removal activities suggests a reduction ~88 % in RBT <br />from the initial January abundance (6,570 fish) followiing the March trip (779 fish). Theses <br />analyses also indicate very little change in the abundance ofRBT between the end of the January <br />trip and the beginning of the February trip (~7 fish). However, there was an apparent larger <br />change in the abundance offish between the end oftht: February trip and the beginning of the <br />March. Monitoring by the Arizona Game and Fish Department during April indicated the <br />abundance of fish in the removal reach was approximately 80% of estimates obtained the <br />previously year. However, removal efforts in July 20013 suggested significant immigration into <br />the removal reach had occurred such that starting abundance estimates in July were <br />approximately 60% of the pre-January level. <br />Diet analyses are ongoing, but results thus far indicate low rate of piscivory by rainbow <br />trout and high rate of piscivory by brown trout. Increasing hoop net catches of humpback chub <br />through out 2003 and 2004 may indicate a habitat/survival response by HBC following non- <br />native removal. These data reviewed in conjunction with stock assessment information will <br />provide more definitive information regarding these questions. <br />The success in the first months of the experiment, prompted GCMRC to examine and <br />propose a modification to the original plan for mechanical removal. The modification extended <br />the original area of removal downstream to RM 72.7, adding 7 miles to the area below the LCR. <br />During 2004, removal areas and depletion pass numbers were increased. Four depletion passes <br />in the original reach (RM 56.2-65.7) and 4 depletion passes in only the upper part of the <br />expanded reach (65.7 - 68.5; Lava Canyon to Tanner Canyon) were conducted. This design <br />permits adequate removal efforts to maintain low non-native abundance and an expansion <br />beyond the originally proposed reach. This compromise should strengthen the experimental <br />treatment and increase both the likelihood that a change in HBC survival and recruitment will <br />occur as well as our ability to detect such an increase. <br />Mechanical removal was continued into FY05 and is proposed in this work plan for a <br />fourth year. It will be implemented as per recommendations from the Adaptive Management <br /> <br />GCMRC FY2006 Annual Work Plan (Draft February 15,2005) <br />