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This article comprises the first presentation of data regarding the growth and distribution of juvenile Atlantic sturgeon, Acipenser oxyrinchus Mitchill, released into the Drwęca River (Vistula drainage basin). In the 2007-2009 period, 2097 sturgeon tagged with Carlin tags were released into the Drwęca River. Information obtained from recapture referred to just under 2.3% of all the fish released. The sturgeon were caught most frequently in the Gdańsk Bay and in the Vistula estuary from March to December, with two periods of more intense catch noted in July and October. The time elapsed between release and capture ranged from 28 to 352 days and depended on the size of the fish at release. The absolute growth of juvenile sturgeon increased throughout the period they spent in open waters; however, this period had no impact on the body length daily growth rate.
This article presents the results of a study of the dietary composition of juvenile Atlantic sturgeon caught in the Drwęca River and in Maltańskie Reservoir. Among the fish caught in the Drwęca, 67% had empty digestive tracts. In terms of numbers, the greatest share of the dietary composition of juvenile sturgeon from the Drwęca River was of Oligochaeta and larval Chironomidae, while the greatest weight contribution was made by larval Trichoptera. Larval Chironomidae, Oligochaeta, and Simuliidae were the most frequent components of sturgeon food. In comparison to the diet of fish from the Drwęca River, that of the fish caught in the Maltańskie Reservoir was more homogeneous as it was comprised exclusively of flies. Larvae of the genus Chironomus dominated numerically, followed by those of Procladius sp., Einfeldia sp., and Polypedilum sp. The analysis of juvenile Atlantic sturgeon food composition indicated that benthic organisms are the most important dietary component. In the natural lowland river the food spectrum of the juvenile Atlantic sturgeon was much wider than that of the fish in the dam reservoir.
Aura
|
1997
|
nr 10
18-19
Mismanagement can cause degradation of the environment. Such a nature reserve as the Drwęca River should be under special protection. Local governments have been aware of this for quite some time. In more than a decade, all the towns over the Drwęca River commissioned municipal waste water treatment plants and secured sites for safe solid waste disposal. The author describes natural, tourist and recreation-related attractions in these towns and the projects aimed at environmental improvements.
e size, length/weight relationship, sex ration and gonadosomatic index of the autumn and spring upstream run populations of the river lamprey have been studied. The size attained by the lampreys from the lower Vistula basin (Drwęca R.) is among the largest recorded for this species. In autumn males in the studied rivers outnumber females. In this period lampreys are bigger than during the spring run. The mass of gonads and the GSI in early spring are higher than in autumn.
The plastic and meristic characters of the river lamprey were studied in 145 specimens of the autumn and spring run populations from the north-Polish rivers (the Grabowa, Drwęca, Wda, Parsęta). Among the examined lamprey populations entering the Polish rivers in autumn no essential differences in body proportions are observed. In comparison with autumn populations, the lampreys that start their spawning migration as late as spring differ more considerably with respect body proportions. Besides, they are characterised by more marked sexual dimorphism, which can be related to more advanced development of gonads.
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