Age Estimation for Shovelnose Sturgeon: A Cautionary Note Based on Annulus Formation in Pectoral Fin Rays

Abstract

Numerous studies have examined the age and growth of shovelnose sturgeon Scaphirhynchus platorynchus, but only one study attempted to validate age estimation techniques. Therefore, our objective was to use marginal increment analysis to validate annulus formation in pectoral fin rays of shovelnose sturgeon collected from the Missouri River. We also compared the precision of age estimates between two different readers. Marginal increment distance indicated that for most of the populations an opaque band was laid down in pectoral fin rays during the summer. However, opaque bands were formed throughout the year in some individuals, which could be problematic when using fin rays for age estimation. The agreement of age estimates by two readers for shovelnose sturgeon was only 18%, and differences in ages between the two readers increased for older fish. The presence of split annuli, false annuli, spawning bands, imbedded rays, and deteriorating sections made individual growth rings difficult to separate. Our findings verified that opaque bands are formed annually during the summer in the pectoral fin rays of most shovelnose sturgeon, but some individuals form opaque bands during other times. Pectoral fin rays will probably continue to be the most practical method of age estimation in shovelnose sturgeon, but ages estimated by this method should be used with caution.

A validated, minimally deleterious method for aging sturgeon

“…All structures except the fin spine have proved to be detrimental to or have required sacrifice of the fish (Brennan and Cailliet, 1989); therefore, the most widely used aging structure for sturgeon species is the fin 2 Nakamoto, R. J., T. T. Kisanuki, and G. H. Goldsmith. 1995 spine (Rien and Beamesderfer, 1994;Rossiter et al, 1995;Stevenson and Secor, 1999;Berg, 2004;Hurley et al, 2004;Whiteman et al, 2004;Allen et al, 2009). Kahn and Mohead (2010) advised against the use of the fin spine in mature shortnose, Atlantic, Gulf, and green sturgeon because of increased reader error, abnormal regrowth, and an increased chance of deleterious effects.…”

“…Another important aspect of age and growth that is often ignored is the validation of annual band formation in aging structures (Beamish and McFarlane, 1983;Campana, 2001). Despite the widespread use of the pectoral spine for age estimation (Rien and Beamesderfer, 1994;Rossiter et al, 1995;Morrow et al, 1998;Stevenson and Secor, 1999;Hurley et al, 2004;Whiteman et al, 2004), successful validation of annual band formation in the pectoral spine has been published for only 2 North American sturgeon species: white (Rien and Beamesderfer, 1994) and lake (Rossiter et al, 1995) sturgeon. Accurate age estimation is critical because it forms the basis for calculating growth and mortality rates, age at maturity, and estimates of longevity, all of which are essential for the production of accurate population models.…”

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

“…Many sturgeon studies have operated under the assumption that a set of opaque and translucent bands on fin ray cross sections represent 1 year of life. However, only a handful of studies have attempted to validate age estimates using pectoral fin rays in North American sturgeon (Rien and Beamesderfer 1994;Rossiter et al 1995;Bruch et al 2009;Koch et al 2011;Hamel et al 2014), and only one, specifically, for Shovelnose Sturgeon Scaphirhynchus platorynchus (Whiteman et al 2004).…”

A Comparison of Methods to Estimate Shovelnose Sturgeon Mortality in the Mississippi River Adjacent to Missouri and Illinois

“…Catch-at-age data are commonly used to estimate mortality for commercially exploited species, but inaccurate age assignment to individual fish in a sample can bias mortality estimates. It is well documented that sturgeon species are difficult to age (Brennan and Cailliet 1989;Rossiter et al 1995;Whiteman et al 2004); however, Shovelnose Sturgeon pectoral fin rays provide the most precise age estimates and are readily used Tripp et al 2009). Mortality rates (e.g., rates above a predetermined threshold) of Shovelnose Sturgeon populations have been used to establish harvest regulations (WDNR 2007;Koch et al 2009; D. P. Herzog, unpublished; G. Scholten, Iowa Department of Natural Resources, personal communication), but the method that provides the most reliable mortality estimate remains unclear.…”