Updated assessment of hatchery-reared pallid sturgeon (Forbes & Richardson, 1905) survival in the lower Missouri River By K. D. Steffensen 1 , L. A. Powell 2 , S. M. Stukel 3 , K. R. Winders 4 and W. J. Doyle 5 1 Fisheries Division, Nebraska Game and Parks Commission, Lincoln, NE, USA; 2 School of Natural Resources, University of Nebraska-Lincoln, Lincoln, NE, USA; 3 South Dakota Department of Game, Fish and Parks, Yankton, SD, USA; 4 Missouri Department of Conservation, Missouri River Field Station, Chillicothe, MO, USA; 5 U.S. Fish and Wildlife Service, Columbia Fish and Wildlife Conservation Office, Columbia, MO, USA Summary As pallid sturgeon, Scaphirhynchus albus (Forbes & Richard- son, 1905), natural reproduction and recruitment remains very minimal in the lower Missouri River from Gavins Point Dam (river kilometer [rkm] 1305.2) to the confluence with the Mississippi River (rkm 0.0), hatchery supplementation and river-wide monitoring efforts have continued. Annual survival estimates of hatchery-reared pallid sturgeon stocked in the lower Missouri River were previously estimated during 1994–2008. Low recapture rates prior to 2006 limited the data available to estimate survival, which resulted in consid- erable uncertainty for the estimate of annual survival of age- 1 fish. Therefore, the objective was to provide more precise estimates of annual survival of pallid sturgeon using five additional years of stocking and sampling. The Cormack- Jolly-Seber model structure provided in program MARK was used to estimate the age-specific survival estimates. Over 135 000 hatchery-reared pallid sturgeon were released during 1994–2011 and recaptured at a rate of 1.9%, whereby esti- mates for the annual survival of age-0 (Ø = 0.048) and >age- 1(Ø = 0.931) were similar to those previously reported, but the age-1 (Ø = 0.403) survival estimate was 52% lower. Post hoc analysis using time-specific survival estimates indicated lower survival for age-1 fish post-2003 year classes, relative to the pre-2002 year classes. An analysis confirms that hatch- ery-reared pallid sturgeon continue to survive in the wild. However, low survival during the first 2 years of life is a management concern as efforts are aimed at maximizing genetic diversity and population growth. A follow-up analy- sis also demonstrated the variability of capture rates and sur- vival over time, which reinforces the need to continue to monitor and evaluate mark-recapture data. The mark-recap- ture efforts have provided demographic parameter estimates that remain a critical component for species recovery as these data are incorporated into population models. Introduction Typically, survival or mortality estimates are used in fisheries management to determine harvest regulation, size and bag limits, opening dates or season duration and gear regulations (Noble and Jones, 1999). However for imperiled species, accurate and precise survival estimates are critical compo- nents for species recovery. These survival estimates are used to determine stocking strategies, stocking rates and in popu- lation modeling (i.e. population viability analysis or elasticity analysis) to aid in management and recovery decisions (Gross et al., 2002; Velez-Espino and Koops, 2009; Stef- fensen et al., 2013a). The precision around these mean sur- vival estimates increases the accuracy of these population models to determine the most sensitive parameters and ulti- mately determine the factors limiting species recovery. Highly variable survival estimates lead to highly variable and diffi- cult predictions for population growth and recruitment (Bajer and Wildhaber, 2007). As the precision around these mean estimates are reduced, the prediction power of these models for determining population effects is greatly improved. Therefore given the current focus on world-wide sturgeon recovery, survival estimates are needed to support conservation efforts for these species. Pallid sturgeon, Scaphirhynchus albus (Forbes & Richard- son, 1905), recovery efforts continue through species protec- tion via an endangered species listing (55 FR 36641-36647, United States Fish and Wildlife Service [USFWS], 1990), establishment of a captive broodstock program, hatchery supplementation, and habitat restoration (Dryer and Sand- vol, 1993). Additionally, accidental take of pallid sturgeon has been eliminated through the listing of shovelnose stur- geon, Scaphirhynchus platorynchus (Rafinesque, 1820) under the similarity of appearance clause of the Endangered Species Act (U.S. Fish and Wildlife Service, 2010). Therefore, quan- tifying the survival of these hatchery-reared fish is necessary to determine the effects on the overall pallid sturgeon popu- lation dynamics. The pallid sturgeon is a large benthic species endemic to the Mississippi and Missouri river systems (Bailey and Cross, 1954; Kallemeyn, 1983). Anthropogenic modifications to these large river systems have caused pallid sturgeon popula- tions to become imperiled throughout much of their range as natural reproduction and recruitment remains very minimal (Hrabik et al., 2007; USFWS, 2007; Boley and Heist, 2011; Steffensen et al., 2013a; Eichelberger et al., 2014). Because of these factors, pallid sturgeon remain listed as federally endangered and a Recovery Plan has been developed (Dryer U.S. Copyright Clearance Centre Code Statement: 0175-8659/2016/3201–3$15.00/0 J. Appl. Ichthyol. 32 (2016), 3–10 © 2015 Blackwell Verlag GmbH ISSN 0175–8659 Received: May 30, 2015 Accepted: June 26, 2015 doi: 10.1111/jai.12929 Applied Ichthyology Journal of