Management and Ecological Note Long-term anchor tag retention in yellow perch, Perca flavescens (Mitchill) M. E. LIVINGS, C. W. SCHOENEBECK & M. L. BROWN Department of Wildlife and Fisheries Sciences, South Dakota State University, Brookings, SD, USA KEYWORDS: anchor tag, Floy tag, Perca flavescens, tag loss, tag retention, yellow perch. Tagging and marking techniques are frequently used in ecological studies and are essential for correctly estimating population parameters such as abundance, growth and survival (Buzby & Deegan 1999). Para- meter estimates may be biased when tag loss is incorrectly assumed to be negligible (Muoneke 1992; Guy, Blankenship & Nielson 1996). Many mark– recapture studies have reported high tag losses, which indicates the need to correct for possible tag loss using reliable estimates of tag retention (Ebener & Copes 1982; Muoneke 1992; Hartman & Janney 2006). One method for determining tag retention is to conduct a double-tag study utilising a dependable mark (e.g. fin clip) and a questionable mark (e.g. anchor tag) to estimate tag loss during the time between marking and recapturing (Buzby & Deegan 1999). Results of studies using a redundant marking protocol vary between species. Retention rates of anchor tags after 1 year were 92.0% for largemouth bass, Micropterus salmoides (Lacepe`de), 87.0% for northern pike, Esox lucius Linnaeus, and 49.0% for arctic grayling, Thymallus arcticus (Pallas) (Buzby & Deegan 1999; Gurtin, Brown & Scalet 1999). In addition, tag retention rates can also vary over time. Largemouth bass showed a high tag retention rate of 94.0% after 31 days using anchor tags, but retention rates decreased to 42.9% after 403 days (Hartman & Janney 2006). Anchor tag retention also decreased over time for striped bass, Morone saxatilis (Walbaum), from 42.0% after 1 year to 0.0% after 2 years (Dunning, Ross, Waldman & Mattson 1987) and in smallmouth bass, M. dolomieu Lacepe` de, from 76.0% after 1.5 months to 48.0% after 4 months (Walsh & Winkelman 2002). Observed differences in tag retention estimates for various species and time intervals demonstrate the need for accurate retention rate estimates for differing species and study durations. Pursuant to research requiring estimation of population size of yellow perch, Perca flavescens (Mitchill), information was needed on long-term tag retention. A literature search revealed one short-term retention study (4 days) con- ducted on yellow perch (Scholten, Isermann & Willis 2002); no published literature on long-term anchor tag retention in yellow perch or other percids was found. Therefore, the objective of this study was to estimate long-term anchor tag retention for yellow perch in natural lakes. The two study areas were Lake Cochrane and Lake Madison, South Dakota, USA. Yellow perch were collected with trap nets from both lakes during April to May 2005. A total of 253 yellow perch on Lake Cochrane and a total of 601 yellow perch on Lake Madison (total length >100 mm) were collected and marked with a right pelvic fin clip and tagged with an anchor tag. The T-bar anchor tags (Floy Ò tag FD-94) were inserted using an Avery Dennison Ò Mark II tagging gun and were embedded at the base of the dorsal fin through the pterygiophores at a 45° angle to the dorsal–lateral axis (Guy et al. 1996). The gun was rotated 90° before removing the needle to ensure that the T-bar was perpendicular to the pterygiophores on the dorsal–lateral axis (Guy et al. 1996). Fish were recaptured with trap nets in April 2006. A total of 43 double-tagged fish were recaptured from Lake Cochrane and 47 from Lake Madison. Tag retention rates were calculated as the number of yellow perch recaptured with both an anchor tag and fin clip Correspondence: Casey Schoenebeck, Department of Wildlife and Fisheries Sciences, PO Box 2140B, South Dakota State University, Brookings, SD 57007-1696, USA (e-mail: casey.schoenebeck@sdstate.edu) Fisheries Management and Ecology, 2007, 14, 365–366 Ó 2007 The Authors. Journal compilation Ó 2007 Blackwell Publishing Ltd doi: 10.1111/j.1365-2400.2007.00561.x