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Last modified
8/11/2009 11:32:58 AM
Creation date
8/10/2009 5:14:48 PM
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UCREFRP
UCREFRP Catalog Number
9713
Author
VanHaverbeke, D.R.
Title
Stock assessment and fisheries monitoring activities in the Little Colorado River within Grand Canyon during 2004.
USFW Year
2005.
USFW - Doc Type
U.S. Fish and Wildlife Service
Copyright Material
NO
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<br />RECOMMENDA liONS <br /> <br />Since our results for the past four years have important implications concerning <br />the conservation and recovery of HBC, it is recommended that GCMRC continue <br />to pursue options that may enhance native fish populations in Grand Canyon. <br />Primary among these are the reasonable and prudent measures listed in the <br />Final Biological Opinion for the Operation of Glen Canyon Dam (USFWS 1994, <br />USBR 1995). <br /> <br />Second, obtaining annual point abundance estimates for HBC via-closed <br />mark-recapture methodologies is useful and should be continued. However, <br />factors governing population dynamics of trend and abundance are more <br />complex. The use of an open model (e.g., ASMR), which makes use of more <br />extensive data collected over a longer period of time, and provides estimates of <br />recruitment, mortality rates, and abundance trend is preferred (Kitchell et al. <br />2003) and may resolve more difficult questions. In other words, it would be more <br />statistically efficient and robust to incorporate the base data from our annual LCR <br />efforts into open population models for estimating the true trend and abundance <br />of HBC in Grand Canyon (Kitchell et al. 2003). <br /> <br />As an alternative to this approach, it has been advocated by the Upper <br />Colorado River Endangered Fish Recovery Program to sample concurrently in <br />the mainstem and in the LCR in order to obtain an overall closed abundance <br />estimate for the LCR population. The issues with this approach have been <br />spelled out in detail by a panel of mark-recapture experts (Kitchell et al. 2003). <br />Essentially, it is considered more efficient, more precise, and more <br />representative of abundance and trend to utilize a multi-year open model <br />approach (e.g., ASMR) rather than a closed model approach. Second, in order <br />to run a concurrent estimate, intensive trammel netting in the mainstem will be <br />required. This raises concerns about undue stress and mortality upon the adult <br />fish residing in the mainstem. Entanglement gear, such as trammel nets, is <br />known to be more stressful than entrapment gear, such as hoop nets (Hopkins <br />and Cech 1992). Third, a switch towards a concurrent sampling methodology is <br />expected to be costly, and is viewed by some as not making use ofthe best <br />available scientific information (USGS 2004). For all of the above reasons, it is <br />suggested that GCMRC continue its current strategy of obtaining closed <br />population estimates in the LCR, and incorporating these data into open models. <br /> <br />Third, it is recommended that sampling activities are continued in the LCR <br />during spring months. At this time, it is unknown what the discrepancies in ratios <br />of ripe males to females may imply biologically. In addition, data collected in <br />spring are preferred for current ASMR modeling efforts because the large <br />number of fish captured improves the accuracy and precision of many aspects of <br />the model (Kitchell et al. 2003). <br /> <br />30 <br />
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