Relative Bias and Precision of Age Estimates among Calcified Structures of Spotted Gar, Shortnose Gar, and Longnose Gar

Abstract

Recreational angling for gars (family Lepisosteidae) has become more popular in recent years; however, the fundamental understanding of their population dynamics needed for effective management and conservation is lacking. Age data are essential for describing population dynamic rate functions, but few studies have addressed the selection of ideal calcified structures for estimating age in gars. We collected Spotted Gars Lepisosteus oculatus, Shortnose Gars L. platostomus, and Longnose Gars L. osseus from 12 Illinois water bodies to assess the relative bias and precision of age estimates derived from branchiostegal rays, pectoral fin rays, cleithra, and sagittal otoliths. Age assignments differed among these calcified structures for all three species. Branchiostegal rays underestimated the age of young fish and overestimated the age of old fish relative to all other structures. Pectoral fin rays consistently underestimated age relative to other structures and produced the lowest mean and maximum age estimates. Although there was low relative bias between readers for all structures, age assignments showed greater variability between readers for old age‐classes when age estimates were derived from cleithra and otoliths. Between‐reader precision was highest using pectoral fin rays, whereas cleithra and otoliths generated lower coefficients of variation and percent agreement values. These findings reveal a need to improve or modify structure processing methods to increase readability when cleithra and otoliths are used for age estimation. Given these results, future validation studies should target branchiostegal rays and pectoral fin rays to determine the most accurate calcified structure for aging gars.

Comment: The Challenge of Age Estimation in Gars Lepisosteus spp.

“…() and King et al. () viewed sagittal otoliths and pectoral fin rays in the same cross‐sectional plane, but the techniques used to obtain the sections differed and it is unknown how these differences affected age estimation. In Buckmeier et al.…”

“…; King et al. ; see Table ). Second, the inability to validate age estimation methods and the poor corroboration among calcified structures raises concerns about the reliability of previously published age estimates for Lepisosteus and subsequent inferences about life history and age‐related metrics for the genus.…”

“…() and King et al. () both reported poor precision among structures as well as between experienced readers for given structures. Poor correlation among structures is often attributable to inconsistent annulus formation in one or more of the structures (i.e., process error).…”

“…Branchiostegal rays underestimated the age of young fish and overestimated the age of older fish, while pectoral fin rays also consistently underestimated the ages of Illinois lepisosteids relative to other structures (King et al. ). Branchiostegal and pectoral fin rays have been shown to underestimate the age of other ancient freshwater fishes, including Alligator Gar (Buckmeier et al.…”

“…(, this issue) used oxytetracycline (OTC) to validate annual increment formation in calcified structures of Lepisosteus in Texas, whereas King et al. (, this issue) examined relative bias and precision among structures and readers of unknown‐age Lepisosteus spp. in Illinois.…”