BENEFITS FROM FISH STOCKING - EXPERIENCES FROM STOCKING YOUNG-OF-THE-YEAR PIKEPERCH, STIZOSTEDION-LUCIOPERCA L. TO A BAY IN THE BALTIC SEA

To evaluate the economic viability of fish stocking, it must be possib le to identify the stocked fish in the wild. To find a suitable markin g method, young-of-the-year (YOY, length 8-10 cm) pikeperch (Stizosted ion lucioperca) were tagged in different ways and stocked in ponds. Ov er a 185-day winter period, there was no significant size-dependent mo rtality, but clear differences in mortality among fish marked in diffe rent ways. Fingerling and streamer-tagged fish had significantly lower survivorship than fin-clipped (left pelvic fin) and colour-marked (Al cian Blue) fish, which were not different from controls. Seventeen tho usand, seven hundred sixty-six YOY pikeperch were fin-clipped and rele ased in a large bay of the Baltic Sea on the Swedish east coast in Oct ober 1991. The following year, 23% of all 1-yr-old fish caught came fr om this stocking. The proportion of marked fish was considerably highe r close to the release site, showing that they were relatively station ary during their first year of life. A simple economic analysis demons trates that pikeperch stocking can be very profitable. Based on the ca pital invested in the stocked YOY, the economic yield corresponds to a n annual interest rate of 43%. (C) 1997 Elsevier Science B.V.