G. Cvijanović

Liver, gills, and skin histopathology and heavy metal content of the Danube sterlet (Acipenser ruthenus Linnaeus, 1758).

The sterlet (Acipenser ruthenus L.) is a bottom-feeding fish species with a direct exposure to contaminants from water and sediments. Although heavy metal pollution is believed to be one of the main threats to the sterlet population in the Danube River basin, there is a lack of knowledge of the exact impact of heavy metals on their survival. In the present study, effects of heavy metal pollution on sterlet in the Danube basin were assessed as well as the utility of different sterlet organs and tissues as indicators of heavy metal contamination. The sterlet were sampled at three different sites in the Danube basin, in Hungary and Serbia, isolated from each other by dams. Heavy metal analysis included measurement of Cd, As, Pb, Cr, Hg, Cu, Ni, Fe, Mn, and Zn concentrations in sterlet gills, muscle, liver, and intestine, and histopathological analyses comprised assessment and scoring of the extent and intensity of alterations in skin, gills, and liver tissue. Analysis revealed a significant presence of sublethal histopathological changes that were most pronounced in the liver and skin and increased accumulation of heavy metals, with the highest concentrations in the liver. Canonical discriminant analysis showed significant differentiation among the three studied localities, suggesting that the heavy metal concentrations in sterlet populations were site specific. The present study concludes that the accumulation of heavy metals is a response to the presence of these pollutants in the environment, and, together with other pollutants, it affects the vital organs of natural sterlet populations.

Assessment of Extinction Risk and Reasons for Decline in Sturgeon

Sturgeon populations in the Danube River have been affected by a combination of hydropower development, over-harvesting, habitat degradation from agricultural and industrial practices and from urbanization. The effects of these changes have been monitored on six sturgeon species inhabiting the Danube River. Two of them are resident species, while the other four migrate to the river for spawning. Atlantic sturgeon (Acipenser sturio) has completely disappeared from this region. Ship sturgeon (Acipenser nudiventris) is very rare in professional fishing catches. Beluga (Huso huso), Russian sturgeon (Acipenser gueldenstaedtii), stellate sturgeon (Acipenser stellatus) and sterlet (Acipenser ruthenus) are endangered with different levels of extinction risk. Here, we model the time dependence of the beluga and Russian sturgeon catch in the Serbian part of the Danube River. Predicted extinction of Russian sturgeon was estimated to fall around the middle of the century, and for beluga approximately at middle of the millennium. Suggestions for sturgeon conservation measures on a national level and coordination of all relevant institutions in Serbia are also presented.

Trends in Fisheries Science from 2000 to 2009: A Bibliometric Study

The present study applies a bibliometric approach to identify recent patterns and trends in the methods, subjects, and authorships in the literature published in fisheries science (2000–2009). The results indicate that the most frequently studied group of species were Salmonidae, although the interest for these species seems to be diminishing. The studies of the marine habitat and inland habitats, respectively, have revealed a marked increase and decrease in frequency. Genetics represents the most rapidly growing area of research. The model development was the most frequently applied method in fisheries science, although such publications have had a generally lower number of citations. The number of experimental studies was markedly low, but they were also the most frequently cited. The United States was the most productive country over the last decade with a gradually increasing output over the time, but it was surpassed by the total European Union output. An apparent difference in the research output has been recorded between the developed and developing countries. The findings of this study, however, indicate a positive tendency in this direction. A growing rate of publications based on international collaboration was recorded, and such publications also demonstrate a higher number of citations than the single-country publications.

Insight into Danube sturgeon life history: trace element assessment in pectoral fin rays

Sturgeon populations in the Danube River have experienced severe decline during the last several decades, mostly due to the poorly regulated fishery, river fragmentation and water pollution. This study focuses on gaining better understanding of sturgeon life history primarily by addressing the assessment of microelement accumulation in sturgeon pectoral fin rays, especially of strontium and calcium, as a method that can reveal migration patterns of anadromous sturgeons. Analysis was performed on pectoral fin samples of three anadromous Danube sturgeon species (beluga, Russian sturgeon and stellate sturgeon) by the use of a Nuclear Microprobe technique. The most frequent pattern in analyzed samples was represented by a low Sr:Ca ratio in the innermost annuli, followed by an increased ratio in the middle annuli segment, and often with a decreased ratio in the outermost annuli. Probability density estimate has revealed three distinguished maxima of the Sr:Ca ratio, 7.08 × 10−3, 8.98 × 10−3 and 9.90 × 10−3, which might correspond, respectively, to fresh, brackish and saltwater. Although the analysis of the Sr:Ca ratio in sturgeon pectoral fin rays has revealed changes that might indicate probable migration between habitats with different water salinity, further studies are needed for improvement of this method. This study represents the first analysis of this kind that was conducted on sturgeon species from the Black Sea basin.

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.

Demographic flexibility influences colonization success: profiling invasive fish species in the Danube River by the use of population models

Invasive species have the ability to modify their life-history traits in newly colonized areas, with positive shifts in specific life history traits under favourable environmental conditions. If such positive changes in their life history result in a comparably larger population growth rate, it may give them a competitive edge over native species, support faster range expansion and contribute to their invasion success. Within the present paper we hypothesized that the demographic flexibility represents an important contribution to the invasion success of exotic species, and that demographic flexibility patterns of invasive species differ from those in unsuccessful invaders. We tested this hypothesis by the use of elasticity analysis applied on simple age-structured population models of invasive fish species in the Danube River, as well as of non-native species that failed to establish or become invasive. Findings imply that the invasive fish species could have the ability to experience a more rapid population growth under favourable environmental conditions, especially those that sustain recruitment, while at the same time being more robust to changes in survival. The highest population elasticity among the assessed alien invasive species was detected in stone moroko (Pseudorasbora parva). The described approach has the potential to be used as an additional screening tool for invasive species. When combined with other invasion risk profiling methods, it can provide additional insight into characteristics of species invasions and in invasion potential of a species.

Population Viability Analysis of the European Sturgeon (Acipenser sturio L.) from the Gironde Estuary System

This study presents a population viability analysis (PVA) conducted on the Gironde population of Acipenser sturio using the Vortex software package. As identified by the model, the most important objects of the future research efforts related to A. sturio life history should be the determination of the mean fecundity, age at which females reach maturity, female spawning frequency and population sex ratio, as well as the intrinsic population growth rate and the age-specific natural mortality, especially of the youngest age classes. The model has confirmed a high population susceptibility to unsustainable fishery, and a slow recovery potential that can span over a number of decades. The detected lag between the stocking activities and the initiation of the actual population recovery should be taken into account in the planning of restoration projects. PVA should be recognized as an important tool, and integrated within future research, management and policy development efforts.

Erratum to: Insight into Danube sturgeon life history: trace element assessment in pectoral fin rays

Sturgeon populations in the Danube River have experienced severe decline during the last several decades, mostly due to the poorly regulated fishery, river fragmentation and water pollution. This study focuses on gaining better understanding of sturgeon life history primarily by addressing the assessment of microelement accumulation in sturgeon pectoral fin rays, especially of strontium and calcium, as a method that can reveal migration patterns of anadromous sturgeons. Analysis was performed on pectoral fin samples of three anadromous Danube sturgeon species (beluga, Russian sturgeon and stellate sturgeon) by the use of a Nuclear Microprobe technique. The most frequent pattern in analyzed samples was represented by a low Sr:Ca ratio in the innermost annuli, followed by an increased ratio in the middle annuli segment, and often with a decreased ratio in the outermost annuli. Probability density estimate has revealed three distinguished maxima of the Sr:Ca ratio, 7.08×10, 8.98×10 and 9.90× 10, which might correspond, respectively, to fresh, brackish and saltwater. Although the analysis of the Sr:Ca ratio in sturgeon pectoral fin rays has revealed changes that might indicate probable migration between habitats with different water salinity, further studies are needed for improvement of this method. This study represents the first analysis of this kind that was conducted on sturgeon species from the Black Sea basin.