Review of the current status of the Atlantic sturgeon Acipenser oxyrinchus oxyrinchus Mitchill 1815, in Poland: principles, previous experience, and results

The article presents the principles of the program to restore the Atlantic sturgeon Acipenser oxyrinchus in Poland and the results obtained to date. Since 2004, various life cycle stages (fertilized eggs, hatchlings, fingerlings) obtained through the controlled reproduction of wild spawners caught in the St John River in Canada have been imported. Broodstocks are held in three facilities, two of which were built specifically for the Atlantic sturgeon restoration programme. From each group of the initial imports from Canada, 50-100 individuals are being held for further rearing. Additionally about fifty individuals from the 1997 and 2001 year classes were transferred from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (Berlin, Germany). These are also the offspring of earlier imports from Canada. Juvenile sturgeons are used for experimental stocking and studies aimed at increasing rearing effectiveness. Rearing early life cycle stages of Atlantic sturgeon was a difficult task, the final results of which remained unpredictable in early trials. The highest losses of larvae are incurred when the fish begin exogenous feeding. Feeding studies focus on the selection of appropriate diets and feeding strategies. The latest results indicate that during the initial feeding period, the fish can be fed once daily. Studies on sturgeon migration were conducted in the Drweca River, and the results indicated that migration rates vary significantly among juvenile sturgeon, with the mean migration rate in spring being lower than in autumn. Currently, the Polish efforts to restore the Atlantic sturgeon focusses on (i) building broodstocks at specialized facilities, (ii) improving hatching and early rearing techniques, (iii) performing experimental stocking with hatchery-reared juveniles, and (iv) acquiring knowledge on the basic elements of the Atlantic sturgeon life history under local conditions. Fertilized eggs of A. o. oxyrinchus will still have to be imported from Canada for several years before self-sufficient production from raised ex-situ brood stocks will become available. The formation of a Polish ex-situ founder population is imbedded in an overall restoration approach in close cooperation with the neighbouring country having shared sturgeon waters and this is in line with the respective international recommendations for sturgeon species conservations.