Validation of Annuli Formation in Pectoral Fin Rays from Shovelnose Sturgeon in the Lower Platte River, Nebraska

Abstract

Fish age is commonly estimated by counting bands on calcified structures. Age estimates are used to calculate information on population dynamics such as growth, mortality, and recruitment. Pectoral fin rays are the most frequently used structure to age sturgeon species, yet little work has been done to validate annuli formation. We collected Shovelnose Sturgeon Scaphirhynchus platorynchus monthly from the lower Platte River, Nebraska, during 2011 and 2012 and removed the leading, left pectoral fin ray from each fish captured. We used marginal increment analysis to assess the validity of annual deposition of growth marks on pectoral fin rays. There were two complete cycles of increasing and decreasing increment values between March and November within each year. Mean marginal increments showed minimal peaks in March, July, and October followed by a decrease in increment length during April, September, and November. However, mean marginal increments were similar between months in both years. These results suggest there is no discernible pattern in growth ring deposition for Shovelnose Sturgeon in the lower Platte River and that their use for age and growth analyses would likely lead to biased estimates. Inaccuracies in age assignment can lead to errors when calculating population dynamic parameters and, ultimately, misguided management decisions. We recommend that alternate methods for estimating the ages of Shovelnose Sturgeon be explored.Received February 25, 2014; accepted July 4, 2014

Habitat use and population characteristics of potentially spawning shovelnose sturgeonScaphirhynchus platorynchus(Rafinesque, 1820), blue sucker (Cycleptus elongatus(Lesueur, 1817), and associated species in the lower Wisconsin River, USA

“…We found blue sucker fin rays difficult to age above 10 years, and we lack confidence in the accuracy of many of our older ages. For shovelnose sturgeon, marginal increment analysis of fin rays indicated that features on the ray that were perceived as annuli did not necessarily correspond to true annual growth marks, suggesting that age estimates from fin rays might be inaccurate (Ruggs, Hamel, Pegg, & Hammen, ). If that is the case, then all ages of shovelnose sturgeon (and perhaps blue sucker as well) are in question.…”

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

“…Presumed fin ray "annuli" were not congruent with age assignments, and estimates of growth from back-calculated estimates were overestimated. In addition, Rugg et al (2014) used marginal increment analysis in an attempt to validate annual growth mark deposition of shovelnose sturgeon fin rays from the Platte River, Nebraska. Annuli were found to be inconsistently deposited on fin rays, and the presence of closely spaced or false annuli was prevalent.…”

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

“…Size at first reproduction was similar between the lower Platte River and the Missouri River for both females and males and less than values reported for the Mississippi and Wabash rivers (Table ). Age at first reproduction was similarly younger in the lower Platte River (Table ); a caveat to this result, however, is that recent research has shown that fin rays do not provide reliable age estimates (Hamel, ; Hamel et al., ; Rugg et al., ). However, Hamel et al.…”