Jörn Gessner

Atlantic sturgeons (Acipenser sturio, Acipenser oxyrinchus): American females successful in Europe

Recent molecular data on the maternally inherited mitochondrial (mt) DNA have challenged the traditional view that the now extinct Baltic sturgeon population belonged to the European sturgeon Acipenser sturio. Instead, there is evidence that American sea sturgeon Acipenser oxyrinchus historically immigrated into the Baltic Sea. In this study, we test the hypothesis that A. oxyrinchus introgressed into, rather than replaced, the A. sturio population in the Baltic. We established four single nucleotide polymorphisms (SNPs) in the nuclear MHC II antigen gene with a species-specific SNP pattern. Using an ancient DNA approach and two independent lines of molecular evidence (sequencing of allele-specific clones, SNaPshot), we detected both A. sturio and A. oxyrinchus alleles in the available museum material of the now extinct Baltic sturgeon population. The hybrid nature of the Baltic population was further confirmed by very high levels of heterozygosity. It had been previously postulated that the immigration of the cold-adapted A. oxyrinchus into the Baltic occurred during the Medieval Little Ice Age, when temperature likely dropped below the degree inducing spawning in A. sturio. Under this scenario, our new findings suggest that the genetic mosaic pattern in the Baltic sturgeon population (oxyrinchus mtDNA, sturio and oxyrinchus MHC alleles) is possibly caused by sex-biased introgression where spawning was largely restricted to immigrating American females, while fertilization was predominantly achieved by abundant local European males. The hybrid nature of the former Baltic sturgeon population should be taken into account in the current reintroduction measures.

Fatty Acid Composition in Sturgeon Caviar from Different Species: Comparing Wild and Farmed Origins

The fatty acid compositions of both lipid classes, triglycerides (TG) and phospholipids (PL), of caviar from 34 specimens of wild caught and 12 farmed specimens were measured. The investigated caviar samples of wild caught sturgeon comprised Huso huso, Acipenser gueldenstaedti, Acipenser stellantus and Polyodon spathula of different origins and those of farmed sturgeon from Acipenser baeri, A. stellatus, and P. spathula, Oleic acid (18 : 1 n - 9) was the dominant fatty acid in TG of all caviar samples. In comparison with the TG, the PL have an elevated content of polyunsaturated fatty acids such as arachidonic (20:4 n-6), eicosapenlaenoic (20 : 5 n-3) and docosahexaenoic acid (22:6 n - 3). In the TG were observed some differences in the fatty acid composition between the caviar samples of the various species, especially in 18 : I n-9 and 20.5 n - 3 hut not in the PL. The proportion of n - 3 to n - b polyunsaturated fatty acids (PUFAs) was independent from the fish species and origins and did not reveal significant differences. The amount of n - 3 PUFAs was in average three times higher compared to n - 6 PUFAs. However, the fatty acid composition of the caviar depends on the origin of the sample, probably caused by differences in the food web. The caviar of farmed sturgeon contained a significant higher amount of linoleic acid (18:2 n - 6) and a lower amount of arachidonic acid, when compared with caviar from wild sturgeon. An explanation could he that sturgeon are not able to convert 18 : 2 n - 6 into 20 : 4 n - 6.

Migratory Behavior of Young Sturgeon, Acipenser Oxyrinchus Mitchill, in the Oder River Drainage. Preliminary Results of a Radio Telemetric Study in the Drawa River, Poland

Migratory Behavior of Young Sturgeon, Acipenser Oxyrinchus Mitchill, in the Oder River Drainage. Preliminary Results of a Radio Telemetric Study in the Drawa River, Poland The movements of individual juvenile sturgeon, Acipenser oxyrinchus Mitchill, during their first stage of downstream migration were observed in the Drawa River, Poland. Two groups of 10 sturgeon each (9 months old, reared in closed recirculation systems) were tagged with internal radio-transmitters. The first group of sturgeon (119-184 g) were tagged with Holohill BD-2N transmitters (weight 0.43 g, operational life 14d) and released on May 7. Fish from the second group (143-206 g) were tagged with BD-2 (weight 1.2 g, operational life 56d) and were released on May 24. The releases took place in the Drawa River below Kamienna Dam, 33 km upstream from the rivers confluence with the Noteć River. All of the fish moved downstream, but migration speeds differed. Seven sturgeon from the first group reached the confluence with the Noteć River, approximately 30 km downstream from the release site, during the first 18 days, which indicated there had been staging intervals in pools. Within four days, six fish from the second group had moved downstream the Drawa River and were located 20 km downstream from the confluence with the Noteć River. The downstream migration speed of the fish correlated with fish size and increased with water temperature. Behawior Juwenalnych Jesiotrów, Acipenser Oxyrinchus Mitchill W Czasie Wędrówki W Zlewni Odry. Wstępne Wyniki Badań Radiotelemetrycznych W Drawie, Polska Obserwowano przemieszczanie się juwenalnych jesiotrów Acipenser oxyrinchus Mitchill w ciągu ich pierwszego etapu migracji w dół rzeki Drawy. Dwie grupy po 10 jesiotrów (9-miesięczne ryby podchowywane w zamkniętym obiegu wody) zaopatrzono w wewnętrzne nadajniki radiotelemetryczne. Jesiotry pierwszej grupy (masa ciała od 119 do 184 g) z nadajnikami BD-2N (Holohill, Kanada) (waga 0,43 g, przeciętny czas działania 14 dni) wypuszczono do rzeki 7 maja. Ryby z drugiej grupy (143-206 g) z nadajnikami BD-2 (waga 1,2 g, przeciętny czas działania 56 dni) wpuszczono do Drawy 24 maja poniżej Elektrowni Kamienna. W trakcie migracji w Drawie ryby lokalizowano ręcznie raz dziennie, natomiast w Noteci raz w tygodniu. Wszystkie ryby przemieszczały się z nurtem w dół rzeki, a tempo migracji poszczególnych osobników było zróżnicowane. Ogólnie dystans 30 km, od miejsca wpuszczenia ryb do ujścia Drawy do Noteci, siedem jesiotrów z pierwszej grupy pokonało w ciągu 18 dni. Sześć ryb z drugiej grupy w ciągu 4 dni od zarybienia spłynęło z Drawy i przemieściło się 20 km od jej ujścia do Noteci. Tempo migracji było dodatnio skorelowane z wielkością ryb i temperaturą wody.

Processing techniques for caviar and their effect on product composition

Various techniques are established to process sturgeon roe to caviar. These processing techniques have significant impact on product composition and quality and thereby marketability. Analysis of caviar samples revealed drastic differences with regard to the gross composition of ova, including water-, protein-, and fat content, which could be linked with the processing techniques utilised. The differences in the preparation processes of the different samples were indicated by the salt contents (NaCl), varying between 3.2% to almost 11.8% between the samples. The elevated salt contents result in dehydration, which increased the concentration of lipids and proteins in a linear pattern. In 28 samples included in the analysis the water contents ranged from 31.5% wet weight to 55.9% wet weight. As a consequence the protein content was reduced from 32.6% to 22.1% wet weight. The lipid content revealed an identical decrease from 20.2% to 10.9% wet weight. It becomes apparent from the high variation of the results, especially for samples with water contents between 47 and 56% wet weight, that other factors besides the salt content are responsible for a significant variability in gross composition. The stage of gonadal development as well as the number of previous spawnings have considerable influences upon the egg-size and its composition.

Prerequisites for the Restoration of the European Atlantic Sturgeon, Acipenser sturio and the Baltic Sturgeon (A. oxyrinchus × A. sturio) in Germany

Acipenser sturio was once a prevalent fish species in all the major rivers of Northern Germany. From the end of the nineteenth century, the population sizes have decreased rapidly. The last large population was observed in the River Eider, where the last specimen was caught in 1969. Under a cooperation agreement with the French Cemagref, the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin received juvenile A. sturio of Gironde origin in 1996 and initiated an ex-situ measure. The main scientific results found since then have been: (1) first gonad maturation occurred in 11-year-old A. sturio (110 to 140 cm total length) kept in freshwater at 20°C under a natural photoperiod; (2) during vitellogenesis the growth factor insulin-growth-like factor (IGF-I) plays an important role as a paracrine modulator, as observed in the model species A. ruthenus; (3) analysis of recent and historical material revealed the presence of the A. oxyrinchus mitochondrial haplotype A in the Baltic. Investigation of the MHC (Major Histocompatibility Complex) nuclear gene, however, showed that these fish carrying this haplotype represent a hybrid population (A. oxyrinchus × A. sturio). The current restoration strategy concerning the Baltic (restocking with A. oxyrinchus) therefore needs to be reconsidered. The mtDNA studies in addition demonstrated the genetic similarity of the Gironde and the North Sea population; (4) A. sturio-specific microsatellites were established for brood stock management of the German and French brood stocks; (5) Evaluation of historical spawning grounds in the River Oder drainage in collaboration with Polish scientists showed intact spawning grounds in the Drawa River.

Potentially threatened: a Data Deficient flag for conservation management

Data Deficient species (DD) comprise a significant portion of the total number of species listed within the IUCN Red List. Although they are not classified within one of the threat categories, they may still face high extinction risks. However, due to limited data available to infer their extinction risk reliably, it is unlikely that the assessment of the true status of Data Deficient species would be possible before many species decline to extinction. An appropriate measure to resolve these problems would be to introduce a flag of potentially threatened species within the Data Deficient category [i.e., DD(PT)]. Such a flag would represent a temporary Red List status for listed Data Deficient species that are, based on the available direct evidence and/or indirect indices, likely to be assigned to one of the threat categories, but where current data remains insufficient for a complete classification. The use of such a flag could increase the focus of the scientific community and conservation decision-makers on such species, thus avoiding the risk that necessary conservation measures are implemented too late. As such, establishment of the DD(PT) category as a kind of alarm for priority species could be beneficial.

Population Conservation Requires Improved Understanding of In Situ Life Histories

This section focuses on future research that should be carried out to contribute to the success of the sturgeon restoration programme. We consider both A. sturio and A. oxyrinchus data to support proposals for future experiments. Three main research topics are proposed: young-of-year behaviour and habitat use in rivers, downstream migration patterns of juveniles, environmental factors influencing migration.

Characteristics of the Reproductive Cycle of Wild Acipenser sturio

This chapter provides data on age at puberty, duration of sexual activity, frequency of spawning, period of spawning, and zones of spawning grounds. Previous data as well as recent information are reported, mainly for the Atlantic population in France. When available, other data have also been mentioned, particularly from the River Guadalquivir (Sp) and the Elbe/Eider Rivers (D). Puberty was reached between 13 and 15 years for males and 19 and 22 years for females. Corresponding length (TL) was 140–145 cm for males and 185 cm for females. Duration of sexual activity was probably in the range of 6–10 years for males and 17–22 years for females. Frequency of spawning is mostly under-documented. The main spawning season is May–June in the Garonne basin. Some characteristics varied with latitude, e.g., age at puberty, onset of reproduction migration. Characteristics of puberty and sexual cycles in farmed sturgeon are given, including the few available data on A. sturio.

Restoration of the European sturgeon, Acipenser sturio L., 1758 in Germany: Effect of Different Feed Items on Specific Growth Rates of Large Juvenile Fish

23 Acipenser sturio juveniles (51 months old, median total length 80 cm, median weight 1950g) of a 1995 artificially reproduced Fl population form the Cemagref, Bordeaux were used for feeding experiments for 28 weeks. Fish were kept in two experimental tanks (5.5 m 3 ) at 20.5 °C and natural photoperiod in freshwater. During the first 16 weeks fish were fed three frozen components (3C), small marine fish (FSMF), small chironomids (FSC) and large chironomids (FLC) except for 3 two weeks periods when the 3 single components were tested: the highest median specific growth rates (MSGR) were obtained with the FLC feed (0.43% bw/d). From weeks 17 to 28 FLC feed was offered except for 2 two weeks periods: a feeding experiment was performed with FLC plus frozen pieces of smelt (MSGR -0.18% bw/d) and a starvation experiment (MSGR -0.32% bw/d). A. sturio showed a high variation in both the MSGR and the individual SGR values thus limiting the interpretation of these quantitative results.

Coupling systematic planning and expert judgement enhances the efficiency of river restoration

Ineffectiveness of current river restoration practices hinders the achievement of ecological quality targets set by country-specific regulations. Recent advances in river restoration help planning efforts more systematically to reach ecological targets at the least costs. However, such approaches are often desktop-based and overlook real-world constraints. We argue that combining two techniques commonly used in the conservation arena - expert judgement and systematic planning - will deliver cost-effective restoration plans with a high potential for implementation. We tested this idea targeting the restoration of spawning habitat, i.e. gravel bars, for 11 rheophilic fish species along a river system in Germany (Havel-Spree rivers). With a group of local fish experts, we identified the location and extent of potential gravel bars along the rivers and necessary improvements to migration barriers to ensure fish passage. Restoration cost of each gravel bar included the cost of the action itself plus a fraction of the cost necessary to ensure longitudinal connectivity by upgrading or building fish passages located downstream. We set restoration targets according to the EU Water Framework Directive, i.e. relative abundance of 11 fish species in the reference community and optimised a restoration plan by prioritising a subset of restoration sites from the full set of identified sites, using the conservation planning software Marxan. Out of the 66 potential gravel bars, 36 sites which were mainly located in the downstream section of the system were selected, reflecting their cost-effectiveness given that fewer barriers needed intervention. Due to the limited overall number of sites that experts identified as being suitable for restoring spawning habitat, reaching abundance-targets was challenged. We conclude that coupling systematic river restoration planning with expert judgement produces optimised restoration plans that account for on-the-ground implementation constraints. If applied, this approach has a high potential to enhance overall efficiency of future restoration efforts.