Marija Smederevac-Lalić

THE KEY THREATS TO STURGEONS AND MEASURES FOR THEIR PROTECTION IN THE LOWER DANUBE REGION

The six native sturgeon species have been commercially harvested in the Danube Basin for more than 2,000 years, with rapid decrease in catch by mid 19th century. Additional negative effect on sturgeon populations in the Danube River was river regulation in Djerdap region, due to navigation in the late 19th century, as well as dam construction in the second half of 20th century that blocked sturgeon spawning migrations. Beside over-fishing and habitat loss, illegal trade, life history characteristics of sturgeon, lack of effective management (due to lack of transboundary cooperation and change in political situation in Lower Danube Region countries) and pollution all pose serious threats on sturgeon populations in Lower Danube Region. International measures established by the Convention on International Trade in Endangered Species (CITES) in late 20th century, listing of beluga (Huso huso) as an endangered species under the U.S. Endangered Species Act, as well as development of Action plan for conservation of sturgeons in the Danube River Basin, had significant impact on activities related to sturgeon protection at beginning of 21st century. These actions were aimed towards diminishment of pressure on natural sturgeon populations and aquaculture development in countries of Lower Danube Region. The main goal of the Action Plan was to raise public awareness and to create a common framework for implementation of urgent measures. Black Sea Sturgeon Management Action Group (BSSMAG) was founded as a consultative body to improve transboundary cooperation among countries in Lower Danube Region. Nevertheless, more actions are necessary in the field of basic scientific investigation, NGO involvement and better connection among all stakeholders. Everyone involved in sturgeon protection must be aware that the sturgeon recovery, as well as their extinction, is a multi-decadal affair, especially for species with long life and late maturing like beluga. Resource users and other stakeholders must be patient enough to support recovery plans, which will allow only small-scaled sturgeon fisheries, or even fisheries that will be performed by some future generations.

Review of sterlet (Acipenser ruthenus L. 1758) (Actinopterygii: Acipenseridae) feeding habits in the River Danube, 1694–852 river km

The aim of this work is to present the variation in the sterlet’s (Acipenser ruthenus L. 1758) diet along the course of the River Danube, from 1694 to 852 river km. The diet of sterlet mostly comprised 12 bottom fauna taxa. Sterlet in the Danube feed mainly on larvae of Trichoptera, Chironomidae (Diptera) and Gammaridae (Amphipoda), with a reduction in food composition variability close to the Djerdap I dam and in the reservoir between the two dams. The other components of the diet were Corophium sp., Asselus sp., Mollusca, Oligochaeta, Annelida, Insecta, Nematoda and Hirudinea. The organisms typical of lithorheophilic and psammorheophilic biocoenoses play a considerable role in the diet of the sterlet. Composition of bottom fauna as food items varies due to changes in environmental conditions induced mainly by the construction of two dams: Djerdap I (943 river km, 1970) and Djerdap II (863 river km, 1984).

The geometric morphometrics and condition of Pontic shad, Alosa immaculata (Pisces: Clupeidae) migrants to the Danube River

Anadromous fish could have intraspecific groups with different life histories; identification of these is very important for management and conservation. Geometric morphometrics represents a quick and cost-effective method to identify such intraspecific groups. In this study, geometric morphometrics of Pontic shad (Alosa immaculata) migrants from the Danube River were investigated, as was Fultons condition factor (K), hepatosomatic index (HSI) and gonadosomatic index (GSI). Pontic shad specimens were collected during April and May of 2004 and 2006. The sample comprised four groups (65 males and 56 females in 2004; 110 males and 78 females in 2006). Geometric morphometrics revealed differences in shape that were statistically significant for both year (nested analysis of variance: F = 13.84; p < 0.001) and sex (nested analysis of variance: sex nested in year, F = 1.71; p < 0.01). The major differences between years were in head shape and position of fins. The most significant difference between females and males was in the dorsolateral expansion of the mid-body section with emphasis on the higher dorsal part of the body. Values for K in this work (0.65–0.70) were the lowest recorded for Pontic shad in the Danube River. Additional investigations involving both geometric morphometrics and molecular genetics are necessary to confirm the presence of races. This could be important information for conservation purposes as Pontic shad is listed as Vulnerable on the International Union for Conservation of Nature list.

Prediction of fish catch in the Danube River based on long-term variability in environmental parameters and catch statistics

The effects of physical factors on fish catch in the Serbian part of the Danube River were studied for period of six decades. The data on total catch for the Danube River from river kilometre 845 to river kilometre 1433 were collected from Statistical Office of the Republic of Serbia, while water level and water temperature data were collected from 16 water gauge stations along the investigated part of the Danube River for the period 1948-2009. Cross-correlation functions have been used to analyse the functional connection between Danube water level, water temperature and fish catch while ARMA model which combines cyclic (deterministic) and random (stochastic) components of the analysed sequences was used for the forecasts. The cross-correlation function showed negative correlation between water level and temperature as well as between water temperature and catch and positive correlation between water level and catch. The Danube water level and catch were coherent at the periods of 2.06, 4.13, 6.2, 10.33, 20.66years, while the cross correlation function between these time series did not show phase lag. The results of reconstruction and forecast of water level, temperature, and catch of fish in the Danube River, obtained by summing the cyclic and stochastic components, was used for the forecast till 2029. In 2016, seven years after, the initial forecasts were made, validity of the model was checked by obtaining data for water temperature, water level and fish catch in the Danube River for the period 2010-2015. Model gave the best prediction for water temperature; average standard error was 1.6 times higher for predicted value than for model value while for fish catch and water level they were 1.96 and 4.97, respectively. Methods used in this work could be powerful tool for prediction of fish catch and serve as the basis for better fisheries management.