Survival to Stage Smolt of One Summer 014. Atlantic Salmon (Salmo Salar L.) Released Into the Gowienica River (Northern Poland) By
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ICES C.M. 19991W:02 Survival to stage smolt of one summer 014. Atlantic salmon (Salmo salar L.) released into the Gowienica River (northern Poland) by J 6zef Domagala I) 2 Ryszard BarteI ,3) 1) Szczecin University in Szczecin, Poland, 2) Inland Fisheries Institute, River Fisheries Laboratory in Gdansk, Poland 3) Sea Fisheries Institute in Gdynia, Poland. Abstract In 1995 and 1997 the respective releases of one summer old Atlantic salmon into Gowienica River reached 9000 and 4500 individuals. The respective average weight of released fish was 0.28 g and 1.0 g. In 1996-1999, some 15 km below the releasing site, a river net pound was used to catch migrating salmon smolts. Out of the fish released in 1995 there were caught 202 smolts, which constituted 2.2 % of recoveries. Length of smolts varied from 13 cm to 24 cm. Out of the second releasing in 1997 there caught 390 smolts, which constituted 8.7 % of recoveries; length of smolts varied from 11 cm to 23 cm. Introduction The last Atlantic salmon population became extinct in Poland in the mid 80's. A restoration program was initiated in 1985 when 50 000 eyed salmon eggs from the Dougava River (Latvia) were imported. During the first 10 years alevins were released into streams but the results were poor. Starting from 1994 smolts have been released into some Polish rivers (Bartel, 1997). A number of stocked smolts have risen to more than 500 000 in 1998. This method is very effective, but in order to avoid domestication of restored salmon population, some numbers of alevins and of one summer old fish are stocked into streams which have good feeding grounds. Better results were obtained from one summer old releasing (Domagala and Bartel, 1997). The aim of these experiments was to get further information on survival of different sizes of one summer old salmon released into streams. Material and methods The experiments were carried out in the upper part of the Gowienica River which flows into the Szczecin Lagoon (Fig. 1). In 1995 and 1997 the respective releases of one summer old Atlantic salmon reached 9 000 and 4500, their average weight being equal to 0.28 g and 1.0 g, respectively. In 1996-1999 the migrating smolts were being caught with the help of a river net pound which was positioned ca. 15 km below the releasing site. In 1996- 1997 the mesh size used was equal to 14 mm, while in 1998-199 it was equal to 11 mm. During the flood period the net pound was removed. Results In 1996 the river net ground was placed in the river on 1 April. The first smolt was caught on 7 April, and the water temperature reached SOC then. The catching period lasted 44 days, that is till 20 May when the water temperature was of 13.8 °C. Over that period smolts were being caught only for 23 days (Table 1) because there were some periods with high water. During that period 151 smolts were caught (1.7 % of recoveries). A number of smolts caught on one day varied from 1 to 27 fishes. In 1997 two year old salmon smolts migrated to the sea for 36 days (from 3 April till 8 May). Water 1 temperature varied then from 7 OCto 9.0 0c. In that period 51 salmon smolts were caught (Table 1); their lengthe varied from 17 cm to 24cm. In 1997 as many as 4500 one summer old salmon fishes were stocked to the same part of the river as in 1995. The difference lied in the fish size, the ones of 1997 weighing 1.0 g, while those of 1995 reaching 0.28 g. The catching period of one year old smolt begun on 20 March 1998 and lasted for 41 days (till 20 May). The first fish was caught on 28 March when water temperature was 4.6 °C. The last smolt was caught on 7 May when water temperature was of 10.3 °C. During those 41 days there were two breaks in catching smolts and that was due high water. For that reason, the catching was conducted practically only for 34 days but nevertheless 178 smolts were caught (4.0 % survival) and their length varied from 11 to 21 cm. In 1999 the observation of smolt migration begun on 1 April and lasted 51 days (till 20 May). The firstsmolt was caught on 4 April at the water temperature of 9.0 °C, while the last one was captured on 3 May at the water temperature of 10.7 0c. Smolt migration lasted for 29 days but fish were being caught only for 21 days (high water). During these days 212 smaIts were caught and their length varied from 17 to 23 cm. The survival to two year old smolt was of 4.7 %. The survival of smaller than one summer old salmon - to small stage (average size 0.28 g) was of 2.2% and it was much lower than in the case of 1.0 g fish released in 1997 2 (survival reached then 8.7%) (Table 1). It can be however supposed that the difference in survival percentage resulted from the breaks in fish catching. References Bartel R. 1997. Preliminary results of restoration of Atlantic salmon (Salmo salar L.) in Poland. Arch. Ryb. Pol. 5,2: 201-207. Domagala J., Bartel R. 1997. Przezycie i wzrost podchowanego i zeruj'lcego wyl((gu lososia (Salmo salar L.) wypuszczonego do malych ciek6w. Komunikaty Rybackie 111997: 15-16. Table 1. Survival of one summer old to small stage salmon in the Gowienica River. Number of Average Year of Year of Number of Number of Average Day of % survival fish weight (g) release catching catching fish length of smolt days caught smolt migration 9000 0.28 1995 1996 23 151 16.2 44 1.7 1997 36 51 19.6 36 0.6 202 17.1 2.2 4500 1.0 1997 1998 34 178 15.1 41 4.0 1999 21 212 18.7 29 4.7 390 16.9 8.7 3 Fig. 1 Site of releasing of one summer old fish and site of catching smolts (arrow). BALTIC SEA 4 .