Investigating Nonlethal Age Estimation in a Lentic Brook Trout Population

Abstract

Routine lethal sampling on small, conservation, or threatened populations may be unsustainable. Therefore, determining if alternative, nonlethal structures can provide accurate age data is important. We evaluated nonlethal structures (scales and pectoral fin rays) in conjunction with otoliths collected from lentic Brook Trout Salvelinus fontinalis in Washington State. We used age‐bias plots, percent agreement, and coefficient of variation to determine how scale or fin ray age estimates compared with otolith estimates, which had been validated in a previous study. Prior experience with aging specific structure types was the primary variable affecting age agreement with validated otolith‐determined age among three age readers. In general, fin rays and scales did not consistently reflect otolith age. Between‐structure coefficient of variation was 17.8–19.1% for scales and fin rays, and between‐structure percent agreement (within 1 year) was 80–82%. Individual percent agreement within 1 year was highest (92% and 86% for fin rays and scales, respectively) and coefficient of variation was lowest (9.0% and 14.8%, respectively) for the most experienced reader. Agreement of age estimates between readers improved with experience aging specific structures. Our study suggests that otolith data remains the preferred option.