Mark–Recapture Validation of Pectoral Fin Ray Age Estimation for Lake Sturgeon

Abstract

AbstractAge estimation is an integral part of fisheries management and is critical for evaluations of growth, mortality, and recruitment. Validation of ages obtained from age estimation of hard parts is a necessary part of the aging process because understanding the magnitude of error and bias associated with structure interpretation provides context for managers using the data. However, validation studies on large‐bodied and long‐lived species, such as Lake Sturgeon Acipenser fulvescens, are challenging. We utilized a 20‐year mark–recapture dataset from Lake St. Clair and the St. Clair River, Michigan, to validate pectoral fin ray age estimates from 51 individuals that were sampled twice, with 2 to 17 years between capture–recapture events. Samples were divided into four quartiles based on mean annual growth rates during their time at large (mean growth for quartiles = 0.6 cm/year, 2.1 cm/year, 3.7 cm/year, and 5.1 cm/year). Age error was defined as the difference between the estimated age of the fish at first and second capture and the number of years at large. No difference in time at large existed among the four groups, but age error differed among the four groups. Additionally, age error did not differ from zero for the two fastest‐growing quartiles but did differ significantly from zero for the two slowest‐growing quartiles. We conclude that for Lake Sturgeon growing faster than 3 cm/year (generally less than 100 cm TL) pectoral fin rays provide valid age estimates. Managers should evaluate the growth rates of Lake Sturgeon in their populations to determine a size threshold for using fin rays for age determination.