The impacts of stocking hatchery reared trout on the native brook trout populations of two streams in central Virginia

Abstract

A two year study to determine the impacts of stocking hatchery reared trout on populations of native brook trout, was conducted on the North and South Forks of the Tye River in Nelson County, Virginia. Areas investigated included: changes in population structures related to the stocking of hatchery trout; harvest of native brook trout during periods of heavy fishing pressure; competition for food among native brook trout and hatchery trout; and changes in native brook trout growth rates, condition factors, and length-weight relationships in stocked and unstocked areas of the two streams. Population estimates of native brook trout during 1977 and 1978 revealed no significant population changes between stocked areas and unstocked areas of both streams. There were, however, highly significant shifts in population densities in all areas of both streams on a seasonal basis; probably the result of severe summer droughts in 1977 and 1978, and heavy winter ice in 1977-78. Native brook trout standing crop estimates dropped 85.0 to 93.1% in both streams in a period of 15 months. A considerable percentage of this reduction in numbers was the result of little or no reproduction during the fall of 1977, resulting in essentially no age O trout in 1978. Creel surveys indicated that native brook trout contributed little to the harvest of trout during periods of extremely heavy fishing pressure. Catch per unit effort (number per hour) figures for native brook trout were considerably higher in unstacked areas than in stocked areas of both streams during times of heavy fishing pressure. Creel surveys also indicated that hatchery trout contributed heavily to the catch for only a short time, with dramatic decreases in fishing pressure shortly after stocking. Food habits analyses on trout from both streams indicated that hatchery trout and native brook trout were primarily opportunistic feeders; taking advantage of the most abundant taxon present in the benthos and drift. Hatchery trout and native brook trout generally fed in separate spatial areas. Hatchery trout appeared to be primarily benthic feeders; however, they fed little on food items of nutritive value, often consuming great quantities of wood, hemlock needles, rocks, and insect exuviae. In contrast, native brook trout preyed on drift organisms in warmer months, shifting to benthic feeding during colder months. Analyses of growth rates of native brook trout indicated that growth rates varied from year to year, depending on standing crop and environmental conditions. During the study, native trout generally grew faster in the long term stocked area of the North Fork. Trout from stocked areas of the two streams were slightly heavier as adults and in better condition than trout in upstream unstacked areas