Current Status and Review of Freshwater Fish Aging Procedures Used by State and Provincial Fisheries Agencies with Recommendations for Future Directions

Abstract

In 2006, the Fisheries Management Section of the American Fisheries Society formed the ad hoc Assessment of Fish Aging Techniques Committee to assess the current status of aging freshwater fish in North America. For seven species groups that included black bass (Micropterus spp.), crappie/sunfish (Pomoxis spp./Lepomis spp.), catfish (Ictaluridae), morinids, percids, salmonids, and esocids, a survey of U.S. and Canadian fisheries agencies (N = 51 agencies responding) revealed that scales, otoliths, and spines were the most common structures used to age fish. Latitudinal clines existed for some of the structures that were examined, with scales typically used more in northern latitudes than otoliths. Many agencies conducted some validation of age estimation techniques and most assessed precision at least for some of the age samples collected. Providing personnel with training to age fish was common. Reasons for the structures used and the types of inferences and information generated from age data were reported. Scales were the most common structure used to age esocids, black bass, crappie/sunfish, and moronids, but only 27% of all respondents felt that scales accurately aged fish to the maximum age. Alternatively, most agencies felt that otoliths provided accurate estimates. From a review of published papers, otoliths were more accurate when compared to other aging structures and showed higher precision. Most agencies conducted back-calculation of lengths from annuli that provided additional information on growth, even though back-calculation procedures contain complex and inconsistent interpretation and computation issues. Currently, many studies are being conducted where known-age fish were chemically or physically marked, stocked, then recaptured after a number of years which can furnish data for age validation. Recommendations include the development of a known-age reference database to allow sharing of information, publication of validation studies, and careful considerations for conducting back-calculation of lengths from presumed annuli.