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554
<br />MARSH ET AL.
<br />never being technically recovered is not unique to
<br />razorback suckers (Lawler et al. 2002; Mann and
<br />Plummer 1995).
<br />High uncertainty around survival and popula-
<br />tion estimates were the result of low recapture
<br />rates: 3-8% of the estimated repatriated fish pop-
<br />ulation for 1999-2002 (Table 2). Additional un-
<br />certainty was due to environmental fluctuations,
<br />varying predation pressure, and other factors. Un-
<br />certainty will decrease and estimates will improve
<br />if more fish are recaptured and estimates of pre-
<br />dation pressure and environmental conditions can
<br />be incorporated into the mark-recapture model.
<br />Another confounding factor involves the rela-
<br />tionship between poststocking growth and survi-
<br />vorship. There was a 34-mm difference in average
<br />size between razorback suckers at release (287
<br />mm) and at later recapture (321 mm), which could
<br />reflect the presence of two segments of the stock
<br />with different growth rates. Growth rate is impor-
<br />tant because it determines how long a fish is sus-
<br />ceptible to predation and therefore affects its long-
<br />term survival. For fish that are the same age at
<br />release, smaller ones are slower growing. If these
<br />slower growing fish were released at a larger size,
<br />their probability of survival would be improved,
<br />but they would still be susceptible to predation for
<br />a longer period of time and therefore have lower
<br />survival compared with faster growing fish re-
<br />leased at the same size.
<br />The repatriation program at Lake Mohave is ap-
<br />proaching its 15th year. Marking of all individuals
<br />released into the lake has allowed assessment of
<br />survivorship and population size as measures of
<br />success. The short-term effort to establish a pop-
<br />ulation of 50,000 fish in Lake Mohave and monitor
<br />the decline of the wild population will continue.
<br />Advancements in mark-recapture models, com-
<br />puter software to assess such models, and an in-
<br />creasing repatriate population will continue to
<br />make the program more efficient and decrease un-
<br />certainty. Although recovery in the traditional
<br />sense may not be achievable in the near future, the
<br />reintroduction program in Lake Mohave will main-
<br />tain for many decades a population that otherwise
<br />would have been extirpated. Some argue that there
<br />is too much emphasis on population size in re-
<br />covery and monitoring efforts for endangered spe-
<br />cies (Campbell et al. 2002; Lawler et al. 2002).
<br />We would argue that, at least for razorback suck-
<br />ers, this must be the focus in the short-term. Only
<br />after a repatriation-based adult population is es-
<br />tablished can the limited research and management
<br />resources be focused on the more difficult task of
<br />species recovery.
<br />Acknowledgments
<br />We acknowledge NFWG members for their con-
<br />tinuing logistic and programmatic support. Thanks
<br />are extended to all participants in field operations.
<br />Special appreciation for their leadership roles to
<br />Tom Burke, U.S. Bureau of Reclamation (USBR);
<br />Mike Burrell, Nevada Department of Wildlife
<br />(NDOW); Andy Clark, Arizona Game and Fish
<br />Department (AZGFD); C. O. Minckley, U.S. Fish
<br />and Wildlife Service (USFWS); W. L. Minckley
<br />(deceased), Arizona State University (ASU); Gor-
<br />don Mueller, U.S. Geological Survey-Biological
<br />Resources Division; and Kent Turner, U.S. Na-
<br />tional Park Service (USNPS). Tom Burke, T. E.
<br />Dowling, Gordon Mueller, and anonymous review-
<br />ers read and provided helpful comments on the
<br />manuscript. Permits from AZGFD, USFWS,
<br />USNPS, and NDOW authorized scientific collec-
<br />tions, and USBR, Boulder City, Nevada, provided
<br />funding for this project. This work was performed
<br />under ASU Animal Use and Care Protocol 05-
<br />767R.
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