STOCKING OF SEA TROUT (Salmo trutta m. trutta) SMOLTS IN POLAND. PART II. FACTORS INFLUENCING RECAPTURES AND VERIFICATION OF ESTIMATES

Abstract

Recaptures of tagged of sea trout smolts released in 1961 - 1986 depended on the place of rearing and on at least two other variables. In case of releases into the Vistula River system the rate of recapture was related to the distance of the releasing place from the sea and to calendar years, exhibiting a decreasing trend. Releases to the Pomeranian rivers and directly to the sea were significantly affected by the mean length of tagged smolts and also by the calendar years. These relationships determined c. 40 % of variation of effects i.e. of weights of recaptured fish per 1000 released smolts. They were used for estimation of expected commercial catches resulting from smolt stocking in 1972 - 1986 and from natural reproduction. The estimated catches differed by an order of magnitude from the real catches. Possible sources of bias were discussed.