Maturation and Reproduction of Shovelnose Sturgeon in the Middle Mississippi River

Abstract

Shovelnose sturgeon Scaphirhynchus platorynchus in the middle Mississippi River provide one of the last commercially viable sturgeon fisheries in the world, yet their maturation and reproduction have not been linked. During 2005 and 2006, we sampled adult and age‐0 shovelnose sturgeon to link age at maturation, the timing and periodicity of spawning, age‐0 sturgeon production, and the resulting age‐0 growth rates. Age at maturity was later than previous estimates, the minimum age of first maturation being 8 years for males and 9 years for females. Total egg count was slightly lower than previously reported (mean = 29,573 per female; SE = 2,472). Males and females typically spawned every 2 and 3 years, respectively. Peaks in mature fish coincided with rising river stages and water temperatures at which shovelnose sturgeon probably spawn. Peaks in spent adults followed. Age‐0 shovelnose sturgeon occurred during June and July 2005 and May and June 2006, confirming successful spawning. Age‐0 sturgeon grew between 0.69 and 1.69 mm total length/d; four distinct weekly cohorts occurred each year. During fall 2006, females contained ripe eggs, males were milting, and a single age‐0 sturgeon (total length = 55 mm) was captured, suggesting that shovelnose sturgeon spawn during fall as well as spring. Management must consider the protracted nature of spawning within seasons as well as differences in spawning activity between seasons.

Range-wide age and growth characteristics of shovelnose sturgeon from mark–recapture data: implications for conservation and management

“…We assumed that the length when growth begins to asymptote was related to the size at reproductive maturity. This assumption was based on several studies examining the reproductive biology of shovelnose sturgeon that reported sexual maturity in the Missouri River and the lower Platte River at approximately 450 mm (Moos 1978;Rugg 2013), whereas fish from the upper and middle Mississippi River and the Wabash River were first mature at approximately 570-615 mm (Kennedy et al 2006;Koch et al 2009;Tripp et al 2009b). The length at maturity of shovelnose sturgeon varied by locations and appeared to be influenced by abiotic or biotic factors.…”

Reproductive traits of shovelnose sturgeon Scaphirhynchus platorynchus (Rafinesque, 1820) in the lower Platte River, Nebraska

“…() and Tripp et al. () (Table ). Individuals were classified as spawners if they had mature ovarian follicles (hereafter referred to as oocytes) or sperm in their gonads, showed evidence of previously carrying mature gametes or were recently spent.…”

“…() and Tripp et al. () (Table ). A McNemar's test was used to compare the classification of sex and stage (binary outcomes) from visual inspections to histological samples.…”

“…Tripp et al. () 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.…”

Assessment of pallid sturgeon relative condition in the upper channelized Missouri River

“…Pallid sturgeons were classified as wild or hatchery-reared according to the presence of a hatchery mark and/or tag or by post hoc genetic determination DeHaan et al 2008). Gender and gonad maturation stage were determined using ultrasound and endoscopic techniques described in Bryan et al (2007) and Divers et al (2009) and fish categorized as reproductive (stage IV, ready to spawn this season) or non-reproductive (stage IIÀIII; Moos 1978; Colombo et al 2007;Tripp et al 2009). The number of eggs released was estimated using volumetric estimation by counting a subset of number of eggs/mL and extrapolating to the total volume extracted.…”