Validation of age estimates obtained from juvenile pallid sturgeon Scaphirhynchus albus pectoral fin spines By J. D. Koch 1, *, K. D. Steffensen 1 and M. A. Pegg 2 1 Nebraska Game and Parks Commission, Lincoln, NE, USA; 2 School of Natural Resources, University of Nebraska, 402 Hardin Hall, Lincoln, NE 68583, USA Summary Pallid sturgeon Scaphirhynchus albus are a federally-listed endangered species, yet little is known about their population dynamics, including age and growth. Age validation is needed before the accuracy of age estimates and ensuing analyses is known. Therefore, we evaluated the accuracy and precision of age estimates obtained from 36 pallid sturgeon recaptured from the lower Missouri River. Accuracy of age estimates varied among three readers from 28 to 41%. Most deviations from the actual age were within 1 year, and most fin spine sections were overaged due to an apparent false annulus near the focus of the section. Between-reader agreement varied by reader combination but was generally around 30%. Our findings suggest that careful attention be paid to age and growth information obtained from hatchery-reared pallid sturgeon fin spines and further methods of accurately estimat- ing age of pallid sturgeon need to be developed. Introduction Many hard structures produce periodic marks used for age estimation of fishes (e.g. scales, otoliths, vertebrae, fin spines, cleithra, opercula), but before age estimates are used, their accuracy needs to be evaluated, including the methodology and the interpretation of growth marks (Beamish and McFar- lane, 1983; Campana, 2001). Inaccurate age estimations can have dramatic affects on age-dependent population metrics (e.g. growth, recruitment, mortality), and can result in the mismanagement of fisheries (Campana, 2001). As such, stan- dard practices recommend that whenever hard structures are used to estimate age of fishes, the method of age determination must be both verified and validated (Beamish and McFarlane, 1983; DeVries and Frie, 1996). Verification refers to the assessment of precision of age estimates which is usually evaluated by two or more readers independently counting annuli on the same hard structure (DeVries and Frie, 1996). These verification assessments might be precise among readers, but they may not necessarily be accurate (Maceina et al., 2007). Validation refers to the accuracy of age estimates and is generally accomplished by assigning age estimates to known- age fish (DeVries and Frie, 1996). The pallid sturgeon Scaphirhynchus albus is native to large rivers in the Mississippi River drainage, has experienced substantial population declines, and has been listed as a federally-endangered species since 1990 (Pflieger, 1997). Little is known about age and growth characteristics of existing pallid sturgeon populations, primarily due to their lack of scales and other calcified structures used for age determination (U. S. Fish and Wildlife Service, 2000; Quist et al., 2004). The most widely-used structure for estimating ages of sturgeons (family Acipenseridae) are sectioned pectoral fin spines (Helms, 1974; Rossiter et al., 1995; Hurley et al., 2004; Whiteman et al., 2004; Killgore et al., 2007; Bruch et al., 2009); however, validation of fin spine age estimates has been attempted for few sturgeon species. Rossiter et al. (1995) validated age estimates of lake sturgeon Acipenser fulvescens by collecting and marking individuals and recapturing a subset of the marked individuals in subsequent years. Rien and Beamesderfer (1994) used a similar study design for validating ages of white sturgeon A. transmontanus. Bruch et al. (2009) utilized bomb radiocarbon assays to assess the validity of lake sturgeon ages obtained from pectoral fin spines and otoliths. Only three attempts have been made to validate age estimates of river sturgeons (genus Scaphirhynchus). Helms (1974) attempted to validate shovelnose sturgeon S. platoryn- chus age estimates using length-frequency histograms, while Whiteman et al. (2004) used marginal increment analysis to validate periodicity of annulus formation in shovelnose stur- geon pectoral fin spines. Hurley et al. (2004) conducted the only age validation study for pallid sturgeon by examining fin spine samples obtained from 16 age-6 fish that were reared and held in captivity until the time of fin spine removal. Although Hurley et al. (2004) reported that pallid sturgeon age estimates exhibited low accuracy and precision, captivity may have affected the growth of individuals and the resulting annulus formation in calcified structures (Campana, 2001). Therefore, the objective of this study was to assess the accuracy and precision of age estimates obtained from multiple age-classes of known-age, juvenile hatchery-reared pallid sturgeon that were stocked in the Missouri River and recaptured at a later date. Materials and methods Pallid sturgeon were collected from the Missouri River, Nebraska (river kilometers 811–1086) during 2007 and 2008 using multifilament gill nets and trot lines baited with nightcrawlers Lumbricus terrestris. All pallid sturgeon were measured to the nearest millimeter (fork length) and the left marginal pectoral fin spine was removed using methods described by Koch et al. (2008). Fin spines were only removed from fish with a unique tag or combination of tags (e.g. PIT *Present address: Kansas Department of Wildlife and Parks, 21514 South Yoder Road, Pretty Prairie, KS 67570, USA. J. Appl. Ichthyol. 27 (2011), 209–212 Ó 2011 Blackwell Verlag, Berlin ISSN 0175–8659 Received: June 15, 2010 Accepted: November 30, 2010 doi: 10.1111/j.1439-0426.2010.01656.x U.S. Copyright Clearance Centre Code Statement: 0175–8659/2011/2702–0209$15.00/0 Applied Ichthyology Journal of