Use of Oxytetracycline Marking to Determine Walleye Stocking Success in Manitoba Lakes

Walleye (Sander vitreus) have been stocked in Manitoba since 1913 to support the high demand from commercial, recreational and subsistence fisheries. However, there has been limited monitoring of the success of stocked walleye in Manitoba and it is not clear to what degree stocked fish contribute to native populations. One of the reasons for this uncertainty is the apparent inconsistency of oxytetracyline (OTC) marking used to differentiate hatchery reared fish from naturally produced fish. The focus of this study was to refine the OTC marking technique by testing the influence of fry density, age at which fry were marked, OTC formulation and water quality of marking solution on mark rate, quality, and persistence. In 2011, otoliths were examined for marks two weeks and three months after OTC immersion. The observed mark rate was used to estimate the total number of stocked walleye in eight Manitoba Boreal Shield lakes. Relative abundance, relative survival and population estimates will be used to estimate the contribution of hatchery reared walleye in each lake.