Finnish Game and Fisheries Research Institute, Helsinki, FinlandSummaryHatchery-reared Atlantic salmon parr and smolts are regularlyreleasedintotheRiverKymijoki,SouthernFinland,toenhancethe local river and coastal fisheries. In 1988–1994, a series ofmicro- and Carlin-tagging experiments were carried out toexamine the influence of stocking age on the stocking results.Five age groups were compared: 1-year and 2-year-old smolts,and 1-summer, 1-year and 2-summer-old parr. The aim was todetermine the most profitable way of producing salmon forfishing in the River Kymijoki. Stocking age had a stronginfluence onthestocking results, measuredastheproportion ofadult recoveries. The most favourable results were obtainedusing 2-year-old smolts (survival index 100), followed by1-year-old smolts (52), 2-summer-old parr (51), 1-year-old parr(37) and 1-summer-old parr (24). Available data on rearingcosts suggest that 2-year-old smolts were also the mosteconomically profitable choice, followed by 1-year-old parr,1-year-old smolts and 1-summer-old parr. The most expensiveway of producing salmon was by stocking 2-summer-old parr.IntroductionThe reduction of the original wild salmon stock of the RiverKymijoki in the eastern Baltic Sea started in the early 1920s, inconjunction with increasing industrial pollution, dredging, logfloating and damming. Eventually, in the early 1950s, RiverKymijoki salmon were driven to extinction, putting an end tothe once flourishing salmon fisheries in the river and in theadjacent coastal areas (Ja¨rvi, 1932).The possibility of restoring the salmon stock of the RiverKymijoki began to improve in the early 1970s, when logfloating ended and the treatment of industrial wastes becamemore effective. First attempts to reintroduce salmon into theriver were carried out in 1974 and regular releases of hatchery-reared fish began in 1979. The extinct original stock of the riverwas replaced by an imported salmon strain from the RiverNeva, Russia.The remaining maximal natural smolt production capacityin the River Kymijoki has been estimated at 100 000 smoltsper year (Mikkola et al., 1990), which is 40% of the pastoriginal production of 250 000 smolts (Sjo¨blom et al., 1974).However, river stretches suitable for salmon reproduction aremostly located above the lowest dams and are only accessibleto spawning migrants via fish ladders in years with a highwater discharge. The continuously accessible river stretches arecapable of producing only up to 3 000 smolts per year.Due to the limited and uncertain potential to revive naturalreproduction, the principal goal of the management of RiverKymijoki salmon has been to revive and maintain the localsalmon fishery in the river and at sea by regular stocking ofhatchery-reared smolts in the estuary and parr into suitablenursery areas in the river. The smolts have been either 2- or1-year-olds on release, and parr have been 1-summer, 1-year or2-summers old.In 1988–1994, two series of tagging experiments were carriedout to examine the influence of stocking age on stockingresults. The aim was to determine the most profitable way ofproducing salmon for fishing in the River Kymijoki.Material and methods