Reproductive traits of shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820) in the lower Platte River, Nebraska By M. J. Hamel 1 , M. L. Rugg 1 , M. A. Pegg 1 , R. Pati~ no 2 and J. J. Hammen 1 1 School of Natural Resources, University of Nebraska – Lincoln, Lincoln, NE, USA; 2 U.S. Geological Survey, Texas Cooperative Fish and Wildlife Research Unit, Departments of Natural Resources Management and of Biological Sciences, Texas Tech University, Lubbock, TX, USA Summary We assessed reproductive status, fecundity, egg size, and spawning dynamics of shovelnose sturgeon Scaphirhynchus platorynchus in the lower Platte River. Shovelnose sturgeon were captured throughout each year during 2011 and 2012 using a multi-gear approach designed to collect a variety of fish of varying sizes and ages. Fish were collected monthly for a laboratory assessment of reproductive condition. Female shovelnose sturgeon reached fork length at 50% maturity (FL 50 ) at 547 mm and at a minimum length of 449 mm. The average female spawning cycle was 3–5 years. Mean egg count for adult females was 16 098  1103 (SE), and mean egg size was 2.401  0.051 (SE) mm. Total fecundity was positively correlated with length (r 2 = 0.728; P < 0.001), mass (r 2 = 0.896; P < 0.001), and age (r 2 = 0.396; P = 0.029). How- ever, fish size and age did not correlate to egg size (P > 0.05). Male shovelnose sturgeon reached FL 50 at 579 mm and at a minimum length of 453 mm. The average male spawning cycle was 1–2 years. Reproductively viable male and female stur- geon occurred during the spring (March–May) and autumn (September–October) in both years, indicating spring and potential autumn spawning events. Shovelnose sturgeon in the lower Platte River are maturing at a shorter length and youn- ger age compared to populations elsewhere. Although it is unknown if the change is plastic or evolutionary, unfavorable environmental conditions or over-harvest may lead to has- tened declines compared to other systems. Introduction Fish populations often decline when reproductively active adults are removed, causing a reduction in reproductive abil- ity and therefore a reduction in sustainability (Ricker, 1954). Sturgeons and paddlefish (Order Acipenseriformes) are among the most endangered fishes worldwide (Birstein, 1993; Birstein et al., 1997). Specifically, shovelnose sturgeon Scap- hirhynchus platorynchus distribution has diminished in the last 100 years due to habitat alteration, overharvest, and water pollution (Keenlyne, 1997). Shovelnose sturgeon have been extirpated in three states, are fully protected in four states, and are considered rare, threatened, or species of spe- cial concern in eight states (Keenlyne, 1997; Koch and Quist, 2010). Facilitating improvements in reproductive potential may help compensate for these declines (Colombo et al., 2007), but a current lack of information about their life-his- tory traits throughout their range limits conservation and management efforts. Specific life-cycle stages of shovelnose sturgeon in various river systems have been investigated (e.g. Colombo et al., 2007; Koch et al., 2009; Tripp et al., 2009). The capture of shovelnose sturgeon in spawning condition indicates that they likely spawn in late April to June when water levels rise and temperatures reach 16.9–20.5°C (Dryer and Sandvol, 1993; Keenlyne, 1997; Tripp et al., 2009). Tripp et al. (2009) found evidence that spawning may also occur in autumn in the middle Mississippi River. However, the magnitude and overall contribution to the population from the autumn- spawned cohorts is unknown. Males first become adults at a fork length (FL) of approximately 450–530 mm (Moos, 1978; Colombo et al., 2007; Tripp et al., 2009) and at an age of 5–8 years (Keenlyne, 1997; Koch et al., 2009; Tripp et al., 2009). Females first become adults at FL 475–600 mm (Moos, 1978; Kennedy et al., 2006; Colombo et al., 2007; Koch et al., 2009; Tripp et al., 2009) and at an age of 6–9 years (Keenlyne, 1997; Koch et al., 2009; Tripp et al., 2009). Adult males appear to have a 2-year spawning cycle, whereas females are thought to have a three- to 4-year spawning cycle (Tripp et al., 2009). Shovelnose sturgeon make upstream movements to spawn, and spawning is thought to occur over hard substrates (Keenlyne, 1997; DeLonay et al., 2007). Fertilized oocytes adhere to the nearby substrate (Holland and Peters, 1989; Simpkins and LaBay, 2007), larvae hatch after 3–5 days (Snyder, 1994) and immediately begin to drift (Moyle and Cech, 1988; Kynard et al., 2002) for 4–5 days (Kynard et al., 2002). Information on egg production provides essential parame- ters for stock assessment and population viability models. These models improve our understanding of population dynamics and allow for the results of management actions to be predicted (Kennedy et al., 2006). Pine et al. (2001) used age-structured models to evaluate long-term population trends of Gulf of Mexico sturgeon Acipenser oxyrinchus deso- toi in the Suwannee River, Florida and concluded that this population was expanding, but that there was a need to define reproductive traits specific to this population, because several model parameters were borrowed from other stur- J. Appl. Ichthyol. (2015), 1–11 © 2015 Blackwell Verlag GmbH ISSN 0175–8659 Received: August 22, 2014 Accepted: January 10, 2015 doi: 10.1111/jai.12785 Applied Ichthyology Journal of