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<br />June 2004
<br />
<br />Hawkins et al.-Aging Colorado pikeminnow
<br />
<br />207
<br />
<br />tons, and techniques for preparing the otoliths
<br />incur more time and expense. Expensive meth-
<br />ods also tend to restrict sample sizes and in-
<br />flate sampling errors (Worthington et a!.,
<br />1995). In addition, vertebrae are not as deli-
<br />cate as otoliths and scales, and would be more
<br />useful for aging preserved specimens.
<br />The lower level of success in aging whole
<br />Qtoliths has been previously recognized for
<br />other fishes in which sectioned otoliths and
<br />vertebral centra were more accurate (Cailliet
<br />et a!., 1986; Gettel et a!., 1997; Long and Fish-
<br />er, 2001). An inspection of Fig. 1D suggests
<br />that imprecision in aging whole otoliths occurs
<br />mainly for larger fish, which exhibit slow
<br />growth rates (e.g., 10.2 to 11.9 mm/year; Tyus,
<br />1988; Osmundson et a!., 1997). The first 5
<br />years of growth were detected in otoliths of fish
<br />with a known age, and others have demonstrat-
<br />ed that even daily growth rings can be detected
<br />in otoliths of young Colorado pikeminnow
<br />(Bestgen and Bundy, 1998). Thus, we attribut-
<br />ed lack of precision in reading whole otoliths
<br />from older fish to the difficulty in reading
<br />closely spaced annuli.
<br />Clearly, more samples would have benefited
<br />our study, but Colorado pikeminnow is an en-
<br />dangered species, and specimens are rare. Fur-
<br />ther, provisions of the Endangered Species Act
<br />control possession of the fish or its parts. We
<br />encourage others who have access to more
<br />specimens to expand our study, and to use age
<br />and growth data to evaluate the effects of en-
<br />vironmental conditions on the fish across tem-
<br />poral and spatial boundaries. Differential
<br />growth in various riverine locations or in hab-
<br />itats that have changed over time could pro-
<br />vide valuable insight for use in conservation of
<br />this endangered species.
<br />
<br />)0
<br />
<br />This study was supported by funds, endangered
<br />species permits, and specimens provided by the
<br />United States Fish and Wildlife Service. We thank G.
<br />R Smith for suggesting the use of vertebrae for ag-
<br />ing Colorado pikeminnow and K Seethaler for pro-
<br />viding data and access to specimens he collected. G.
<br />Dean and other United States Fish and Wildlife Ser-
<br />vice employees assisted in collecting specimens and
<br />data.]. F. Saunders, III, provided helpful comments
<br />and assisted with statistical analysis. C. A. Karp re-
<br />viewed and commented on an earlier manuscript.
<br />Mrs. W. L. (Pat) Minckley supported completion of
<br />this paper after the untimely death of her husband.
<br />
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