Age-determination of yellowtail flounder from conventional tagging

Tagging offers a direct and useful approach to validate the age of fish in many marine ecosystems.   This often involves the measurement of partial to complete growth of  hard structures sampled from  uniquely marked fish during release and recapture events.   The technique is often inexpensive, and may be more practical to conduct than age validation experiments.  In this study, we confirmed the age of yellowtail flounder from a large-scale conventional tagging program.  Approximately 4,000 scale samples were obtained from fish that were tagged and released off the Northeast coast of the United States between 2003 and 2005. Scale samples were later collected from 131 recaptured fish from the original marked and released fish, and were processed for marginal increment analysis.  Age was determined by digitizing the scales images.  A light projector was used to select useable scales, identify the focus of the scale, and determine the consecutive annuli or growth checks.  Once the scale impressions were aged, distances from the focus to each annulus were measured using Image Pro-Plus software.  Growth during time at large was determined by measuring the individual annuli, and comparing the measurements between the mark and the recapture events.