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<br />LITTLE COLORADO RIVER HUMPBACK CHUB
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<br />243
<br />
<br />have contributed to uncertainty in each of the assess-
<br />ments, as have reductions in overall sampling effort
<br />since 1995.
<br />
<br />Management Implications
<br />
<br />U.S. Fish and Wildlife Service recovery goals for
<br />humpback chub state that down-listing can proceed if
<br />the following developments occur over a 5-year period
<br />(USFWS 2(02):
<br />
<br />1. The trend in adult (age-4 and older) point estimates
<br />for each of the populations does not decline
<br />significantly;
<br />2. Mean estimated recruitment of age- 3 naturally
<br />produced fish equals or exceeds mean annual adult
<br />mortality;
<br />3. Two genetically and demographically viable, self-
<br />sustaining core populations are maintained such that
<br />the point estimate for each core population exceeds
<br />2,100 adults; and
<br />4. Certain site-specific management tasks to minimize
<br />or remove the threats to the population are
<br />performed.
<br />
<br />The results of the present assessment suggest that
<br />items 1-2 are not being met for the LCR population of
<br />humpback chub. Although our analysis suggests that
<br />there are currently more than 2,100 adults (item 3), at
<br />the present rate of population decline the abundance
<br />will fall below the minimum levels listed within 10--15
<br />years.
<br />fu addition to the concerns they raise relative to ESA
<br />listing status, humpback chub are a central concern in
<br />the design of adaptive, experimental water manage-
<br />ment plans for the Colorado River in Grand Canyon.
<br />Planned and ongoing experimental treatments range
<br />from mechanical removal of nonnative fishes to
<br />wanning of the Colorado River through temperature
<br />control devices on Glen Canyon Dam. Timely
<br />estimates of the responses in recruitment and abun-
<br />dance to these treatments are critical to the experimen-
<br />tal program. None of the methods we have used to date
<br />give quick results, as all ongoing experiments require
<br />several years of monitoring. Our analyses of the
<br />historical data indicate that no existing monitoring
<br />method can provide reliable estimates of such
<br />responses for at least 3 years after the response has
<br />begun. It takes 2-3 years until the larger number of
<br />humpback chub recruits caused by an experimental
<br />treatment have reached the ages at which PIT tagging
<br />can begin to give estimates of abundance, and it may
<br />take several more years until a reliable estimate of the
<br />population trend caused by this recruitment change
<br />becomes evident. Earlier response indications may be
<br />
<br />obtained from index hoop netting in the lower LCR,
<br />but we do not consider such indices reliable enough to
<br />use as a guide for experimental treatment planning.
<br />There is a critical need to develop new abundance
<br />indexing and tagging methods that allow detection of
<br />abundance changes earlier in the life cycle.
<br />
<br />Acknowledgments
<br />
<br />This assessment of the Little Colorado River
<br />population of humpback chub is based on an
<br />assimilation of data collected between 1987 and
<br />present. Many individuals belonging to governmental,
<br />academic, and private institutions contributed to this
<br />database. We acknowledge all the individuals who
<br />have been involved in sampling humpback chub in the
<br />Grand Canyon. fu particular, Arizona State University,
<br />Arizona Game and Fish Department, U.S. Fish and
<br />Wildlife Service, the Navajo Nation, and BioWest
<br />conducted field sampling that contributed importantly
<br />to the database and thus to current understanding of
<br />humpback chub. Permits allowing humpback chub
<br />research have been provided through time by Grand
<br />Canyon National Park, Arizona Game and Fish
<br />Department, U.S. Fish and Wildlife Service, and the
<br />Navajo Nation. We also thank J. Kitchell, C. Grimes,
<br />S. Lindley, D. Otis, J. Rice, C. Schwarz, M. Alldredge,
<br />S. Martell, and K. Pollock for providing an earlier
<br />review and much discussion on the ASMR method and
<br />humpback chub stock assessment in the Grand
<br />Canyon.
<br />
<br />References
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