Use of a Statewide Angler Tag Reporting System to Estimate Rates of Exploitation and Total Mortality for Idaho Sport Fisheries

摘要

From 2006 to 2009, 18,712 fish were tagged and released in 45 tagging events using nonreward and high-reward T-bar anchor tags to estimate the rate of exploitation (u) by anglers in various Idaho fisheries. In total, 3,100 nonreward tags and 592 high-reward tags were reported by anglers. Annual u was adjusted for tag loss, tagging mortality, and angler tag reporting rate. Tag loss, estimated by double-tagging a subsample of fish, varied greatly among species; tag loss was lowest for Yellow Perch Perca flavescens (1.1% in year 1 and 4.5% in year 2) and crappies Pomoxis spp. (2.9% and 4.8%) and was highest for Largemouth Bass Micropterus salmoides (14.8% and 30.3%), Walleyes Sander vitreus (11.4% and 43.2%), and Smallmouth Bass M. dolomieu (10.5% and 41.6%). Short-term (7-33-d) mortality averaged about 1% for both hatchery and wild fish. The nonreward-tag reporting rate averaged 54.5% across all species and years. Adjusted u averaged 19.4% (range = 2.0-44.3%) and was generally highest for crappies (mean = 28.7%) and Smallmouth Bass (22.0%) and lowest for wild trout (9.5%). Estimates of total annual mortality (A), based on the difference in tag returns between years 1 and 2, were plausible for some species but were unusually high for other species, especially Smallmouth Bass and wild trout. The implausibility of some estimates of A probably resulted from a combination of factors, including the reduced vulnerability of larger, older fish to angling, which would have caused a reduction in tag returns in year 2, likely due to a shift in fish behavior or habitat preference as tagged fish grew in size. Our results demonstrate the utility of using the high-reward tagging method to estimate u for fisheries under a variety of circumstances, but fisheries managers should use caution in attempting to simultaneously estimate A from the tag returns.