Are Age Estimates for Longnose Gar and Spotted Gar Accurate? An Evaluation of Sagittal Otoliths, Pectoral Fin Rays, and Branchiostegal Rays

Abstract

AbstractWe evaluated the accuracy and precision of age estimates from ground sagittal otoliths, sectioned pectoral fin rays, and whole branchiostegal rays of Longnose Gar Lepisosteus osseus and Spotted Gar Lepisosteus oculatus using fish marked with oxytetracycline (OTC). The presence of OTC time stamps in these calcified structures and the ability to correctly identify post–time stamp annuli varied greatly. We identified time stamps in 66.7% and 91.7% of the otoliths and 43.8% and 61.4% of the pectoral fin rays for Longnose Gars and Spotted Gars, respectively; OTC marks were not observed in branchiostegal rays. Annual increment periodicity was validated in ground sagittal otoliths through age 10 for both species. For fish older than age 10, accuracy declined to about 60%, with most estimates being less than the number of post–time stamp annuli by 1 year. Age estimates derived from pectoral fin rays were consistently less than the number of post–time stamp annuli because OTC marks were generally associated with the outer edge of this bone. Overall accuracy from pectoral fin rays was only 14.3% for Longnose Gars and 22.6% for Spotted Gars. Although the lack of time stamps in branchiostegal rays prevented formal evaluation, age estimates derived from this structure were substantially lower than those from otoliths. Precision among readers was poor for all structures, reflecting the difficulties associated with age estimation for these two species. Based on our evaluation, past age estimates from branchiostegal rays and pectoral fin rays should be considered suspect. Ages derived from sagittal otoliths can be reliable through age 10. However, we recommend that readers verify their ability to produce accurate estimates and consider the implications of underestimating age for fish greater than age 10. Future efforts should work to refine or develop alternative preparation procedures for otoliths to improve the visibility of annuli and validate age estimates for older age‐classes.