The success of stocking with hatchery-reared trout has been the subject of varied investigations for the past half-century. Percentage returns are summarised, and literature on the post-stocking movements of hatchery-reared trout is reviewed. Factors affecting the poststocking movements are considered, special attention being paid to studies on industrial rivers. Highest returns are obtained from stockings, with trout of a size suitable for angling, made during or shortly before the angling season. The majority of stocked brown trout, Sulmo truttu tend to remain close to the area of stocking, but brook trout, Sulvelinus ,fontinah and rainbow trout, Sulrno guirdneri show greater movement, usually in a downstream direction. Greater dispersion of all species occurs if they have overwintered prior to capture or have been stocked in ' cold water ' or in small upstream stretches of river.

Accelerator mass spectrometry (AMS) has been used to measure Pu activities and 240 Pu/ 239 Pu isotope ratios in samples contaminated by releases from the Mayak nuclear installation. Determination of Pu isotopes in high-level samples indicated that the ratio of 240 Pu/ 239 Pu in waste has increased toward the present. The lowest 240 Pu/ 239 Pu atom ratios, 0.012-0.024, were found at the Asanov Swamp, where the primary source of contamination was discharge of intermediate-level radioactive waste between 1949 and 1951. The highest ratios, 0.06-0.29, were found in industrial reservoirs contaminated by various sources of waste up to the present day. Measurement of Pu isotopes in low-level samples collected from the Techa, Iset, and Ob Rivers showed that while activity levels decrease with distance from Mayaksfrom 2000 Bq/kg at 7 km downstream to less than 1 Bq/kg sediment at 250 kms 240 Pu/ 239 Pu isotope ratios increase. Results suggest that most of the plutonium in the Upper Techa River originates from the early waste discharges, although enhanced atom ratios in surface sediments downstream (0.035-0.099) indicate a contribution from other sources. On the basis of procedural blanks, detection limits for AMS were below 1 fg of Pu.