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Last modified
7/14/2009 5:01:48 PM
Creation date
5/22/2009 12:31:49 PM
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UCREFRP
UCREFRP Catalog Number
9724
Author
Coggins, L.G., W.E. Pine, C.J. Walters, D.R. VanHaverbeke, D. Ward and H.C. Johnstone.
Title
Abundance trends and status of the Little Colorado River population of humpback chub.
USFW Year
2006.
USFW - Doc Type
North American Journal of Fisheries Management
Copyright Material
YES
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<br />242 <br /> <br />COGGINS ET AL. <br /> <br />8,000 <br />.~7,000 <br />t 6,000 <br />~ 5,000 <br />'84,000 <br />.... <br />~3,OOO <br />S 2,000 <br />::s <br />Z 1,000 <br />o <br /> <br />--+-- Data through 1996 <br />:::~ Data through 1997 <br />---<>-- Data through 1998 <br />_Data through 1999 <br />. .. .... Data through 2000 <br />- . - . - Data through 200 I <br />- Data through 2002 <br /> <br /> <br />~ <br />~ <br /> <br />9::,0, <br />~ <br /> <br />~'\. <br />~ <br /> <br />cu 16,000 <br />.!::! 14000 <br />Vl ' <br />g 12,000 <br />.~ 10,000 <br />'[ 8,000 <br />&. 6,000 <br />'3 4,000 <br />~ 2,000 <br />o <br /> <br /> <br />9::,0, <br />'\.0, <br /> <br />~'\. <br />~ <br /> <br />~,." <br />~ <br /> <br />~,." <br />'\.~ <br /> <br />~" <br />'\.~ <br /> <br />~'\ <br />~ <br /> <br />~o, <br />'\.~ <br /> <br />Brood Year <br /> <br />--+-- Data through 1996 <br />- Data through 1997 <br />---<>-- Data through I 998 <br />_ Data through 1999 <br />-- h ... Data through 2000 <br />-.-.- Data through 2001 <br />- Data through 2002 <br /> <br /> <br />~" <br />.~ <br /> <br />~'\ <br />~ <br /> <br />~o, <br />~ <br /> <br />~'\. <br />');~ <br /> <br />Year <br /> <br />FIGURE 6.-Retrospective analysis of age-2 humpback chub recruinnent by brood year (top panel) and adult (age-4 and older) <br />humpback chub abundance (bottom panel) using the first of the three annual age-structured, open-population capture-recapture <br />models (ASMR 1). The trend lines reflect analyses using annually truncated data sets beginning in 1989 and ending as specified <br />in the legend. <br /> <br />based on different total numbers of years of sample <br />data. This retrospective analysis (Figure 6) indicates <br />that the recruitment estimates for the early years (brood <br />years 1987-1992) of the sampling program are quite <br />stable (i.e., are not altered by including more years of <br />data), but that the estimates for the later sampling years <br />are more variable. Additionally, the adult abundance <br />estimates display more variability in both trend and <br />magnitude and generally suggest lower initial abun- <br />dance (1989) and higher terminal abundance (2001) <br />when more years of data are considered. This trend in <br />adult abundance is a result of changes in sampling <br />intensity over time that essentially cause the model to <br />trade off higher mortality estimates with lower capture <br />probability during the years of low sampling intensity <br />(1996-1999). As the analysis is supplied with more <br />recapture data during the 2000--2002 time period, <br />mortality estimates fall and the trend in adult <br />abundance becomes less severe. Although the retro- <br /> <br />spective analysis does not suggest any severe structural <br />problem in model formulation, as there is a general <br />convergence in recruitment and abundance estimates <br />during the early years of data collection, it does further <br />reinforce the need to minimize the variability in <br />sampling effort over time to minimize assessment <br />errors resulting from parameter confounding. <br />All of the evidence suggests that the LCR humpback <br />chub population suffered a major decline in adult <br />abundance between the late 1980s and the present. All <br />of the evidence also points to major declines in <br />recruitment sometime in the 1980s. Though it is <br />difficult to believe that the adult population size <br />remained stable over the 1990s despite these re- <br />cruitment declines, changes in sampling intensity <br />between the early 1990s and early 2000s make it <br />impossible to categorically deny that the adult <br />population size has been stable since 1990. Efforts to <br />improve monitoring since 2000 (e.g., baited hoop nets) <br />
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