Disappearance Of The Spawning Grounds Of The Atlantic Salmon (Salmo Salar L.) In The Drawa And Plociczna Rivers

No abstracts are to be cited without prior reference to the author.

After the Second World War, the only Polish rivers known to be spawning areas for theAtlantic salmon were: tertiary tributary of the Odra River-the Drawa and the left banktributary of the latter-the Plociczna. Within the ~pawning, taking place mainly in the secondand third decade of November, the bright spots of characteristic shape are formed in the river.They are the spawning sites, that can be counted. The main goal of the present paper was toquantifY the spawning sites occurring in the Drawa within 1976-1996. They were studied at thetwo river stretches: 3.7-km-long Drawa section below the weir in the village ofKamienna and2.5-km-long section of the lower Plociczna River, below Ostrowiec Lake. It turned out thatwithin 1976-1985 and 1988 there were 79-2 spawning sites, predominately large, noticed inthe lower Drawa and Plociczna. On the other hand, within 1986-1987 and within 1989-1996,the. spawning sites were not revealed. The number of the spawning sites was distinctlydeclining from 79 in the season of 1985 to 2 in the season of 1988 (Tab. 1). It is presentlysuggested that the major cause of the disappearance of the spawning sites in the Drawa andPlociczna was high fishing mortality of the grown saImon in the Baltic Sea and on the inlandroute oftheir migration-the lower Odra River system in particular.