Douglas A. Dixon, Electric Power Research Institute, 2000 L Street, NW, Suite 805, Washington, D.C., James D. Goins, John E. Olney, and Joseph G. Loesch, Virginia Institute of Marine Science, College of William and Mary, Glouchester Point, VA

Abstract. Annual (1995-1997) stocking of oxytetracycline (OTC) marked larval American shad in the Pamunkey River and subsequent monitoring of juvenile abundance afforded the opportunity to assess the relative contribution of hatchery fish to wild stocks and to investigate the movement of hatchery fish in the nursery zone. Each year, between late March and early May, larval fish (4-7 days age) were stocked at river kilometer 100. Stocked larvae totaled 2.7, 2.0, and 1.3 million for the years 1995 through 1997, respectively. Juvenile relative abundance sampling began the first week of June and continued through mid-August. Excised sagittae were examined with epiflourescent microscopy to detect OTC marks. The number of recaptures each year was nearly proportional to juvenile relative abundance. Recaptures were 14, 147, and 26 fish for 1995 through 1997, respectively. As a percentage of the wild stock, between year variation in the annual recapture frequency was minor (4.7, 7.5, and 3.8%, respectively), suggesting that hatchery fish experienced approximately the same annual natural mortality as wild fish. By early June of each year and throughout the sampling season, the recapture of hatchery fish indicated upstream movement of at least 28-km from the stocking location. The mean size of recaptured and wild fish decreased with upstream distance. Observed behavior suggests that movement upstream is a size-dependent process. Furthermore, because potential swimming speeds may not account for the distance traveled through a strong diurnal tide environment, upstream movement synchronized with flood tide is theorized. Results imply new information on early life history and nursery zone dynamics of larval and juvenile American shad. Recapture information also provides results on American shad restoration efforts and information that can be used to modify stocking practices by the Virginia Department of Game and Inland Fishes.