Recovery and status of shortnose sturgeon in the Hudson River

Shortnose sturgeon (Acipenser brevirostrum), an endangered species, has experienced a several-fold increase in abundance in the Hudson River in recent decades. This population growth followed a substantial improvement in water quality during the 1970s to a large portion (c. 40%) of the species' summertime nursery area. Age structure and growth were investigated to evaluate the hypothesis that improvements in water quality stimulated population recovery through increased survival of young of the year juveniles. Specimens were captured using gill nets bi-monthly from November 2003 to November 2004 (n = 596). Annuli in fin spine sections were used to generate estimates of sturgeon age. Based upon a marginal increment analysis, annuli were determined to form at an annual rate. Age determinations yielded a catch composed of age 5-30 years for sizes 49-105cm Total Length (n = 554). Individual growth rate (von Bertalanffy coefficients: TL, = 1045mm, K = 0.07) for the population was similar to previous growth estimates within the Hudson River as well as proximal estuaries. Hindcast year-class strengths, based upon a recent stock assessment (Bain et al. 2000) and corrected for gill net mesh selectivity and cumulative mortality indicated high recruitments (28,000-43,000 yearlings)during 1986-1992, which were preceded and succeeded by c.5-year periods of lower recruitment (5,000-1 5,000 yearlings). Recruitment patterns were corroborated by trends in shortnose sturgeon bycatch from a Hudson utilities-sponsored monitoring program. Results indicated that Hudson River shortnose sturgeon abundance increased due to the formation of several strong year-classes occurring about five years subsequent to improved water quality in important nursery and forage habitats in the upper Hudson River estuary. (PDF contains 108 pages.)

Nachweis von Parvalbuminen in Störgeweben

Parvalbumins, calcium-binding, heat-stable proteins of considerable allergenic potential, are occurring in high concentration in light muscle of many fish species. Lack of knowledge about parvalbumins in sturgeon tissues prompted us to study the distribution of this type of proteins in light and dark muscle, as well as in swim bladder and skin of Atlantic sturgeon, Acipenser oxyrhynchus, and three other sturgeon species. Results: Light and dark muscle of sturgeons contained water soluble proteins with following properties: (1) Great stability against heating at 70 or 80 °C. (2) Isolelectric points between 3.85 and 5.66. (3) Treatment of proteins separated by isoelectric focusing with the dye “stains all” gave blue protein bands. (4) The molecular mass was about 10 to 14 kDalton. (5) Concentration of acidic, heat-stable proteins was higher in light than in dark muscle. Taken together, these findings gave strong indication for the presence of parvalbumins in muscle tissue of sturgeons. This conclusion was corroborated by immunological tests. However, parvalbumin could not be detected in swim bladder tissue. Skin preparations showed only traces of parvalbumins, possibly resulting from residual muscle tissue.

Variations in year-class strength and estimates of the catchability coefficient of yellowfin tuna, Thunnus albacares, in the Eastern Pacific Ocean

ENGLISH: Year-class composition of catch, virtual population size and yearclass strength were determined from serial samples of size composition of catches and catch records. Murphy's Solution to the catch equation, which is free from the effects caused by changes in fishing pressure, was used to estimate year-class strength, i.e. the total population of fish age 3/4 years. The resultant estimates indicated that the X55, X56, X57, X62 and X63 year classes were above average and the X58, X59, X60, X61 and X64 year classes were below average. The year-class designation refers to the year of actual entry or presumed year of entry into the commercial fishery (at approximately 1 year of age). The strongest and poorest year classes were the X57 and X61 classes, respectively. The ratio of the strongest to the weakest year class was 2.6. This amount of variation is small compared to that found for other species of fish. It was found that the relationship between stock size and yearclass strength is of no value in predicting year-class strength. As a by-product of the analysis, estimates of the catchability coefficients (qN) of the age groups in the fishery were obtained, These estimates were found to vary with age and time. Age-two fish apparently showed the greatest vulnerability to fishing gear, followed by ages three and one, respectively. The average estimate of the catchability coefficient in weight was calculated and found to compare favorably with Schaefer's estimate. The influence of sea-surface water temperature upon year-class strength was investigated to determine whether the latter can be predicted from a knowledge of sea-surface temperatures prevailing during and following spawning. No correlation was evident. SPANISH: La composición de la clase anual en la captura, el tamaño de la población virtual y la fuerza de clase anual, fueron determinados según una serie de muestras de la composición de tamaño de las capturas y de los registros de captura. La Solución de Murphy de la ecuación de captura, que está libre de los efectos causados por los cambios de la presión de pesca, fue usada para estimar la fuerza de la clase anual, i.e. la población total de peces de 3/4 años. Las estimaciones resultantes indican que las clases anuales X55, X56, X57, X62 y X63 fueron superiores al promedio y que las clases anuales X58, X59, X60, X61 y X64 fueron inferiores al promedio. La designación de la clase anual se refiere al año actual de entrada o al año supuesto de entrada en la pesca comercial (aproximadamente a la edad de 1 año). Las clases anuales más fuertes y más pobres fueron la X57 y X61 respectivamente. La razón de la clase anual más fuerte en relación a la más débil fue 2.6. Esta cantidad de variación es pequeña comparada con la encontrada para otras especies de peces. Se encontró que la relación entre en tamaño del stock y la fuerza de la clase anual no tiene valor en predecir la fuerza de la clase anual. Se obtuvieron estimaciones de los coeficientes de capturabilidad (qN) de los grupos de edad en la pesquería como un producto derivado del análisis. Se encontraron que estas estimaciones variaron con la edad y tiempo. Los peces de edad dos aparentemente presentaron la vulnerabilidad más grande en relación al arte pesquero, seguidos por las edades tres y una, respectivamente. La estimación promedio del coeficiente de capturabilidad en peso fue calculada y se encontró que podía compararse favorablemente con la estimación de Schaefer. La influencia de la temperatura del agua superficial del mar sobre la fuerza de la clase anual fue investigada para determinar si se podía predecir esta última según el conocimíento de las temperaturas superficiales del mar prevalecientes durante el desove y después de éste. No hubo correlación evidente. (PDF contains 44 pages.)

Maifische an der deutschen Nordseeküste - zum Auftreten von Finte (Alosa fallax) und Alse (Alosa alosa)

Quantitative data on twaite shad are collected annually in spring and autumn since 1974 by the Demersal Young Fish Survey. Results for occurrence of these anadromous species show that twaite shad has been caught in the entire Wadden Sea area despite of the poorly suited 3-m shrimp beam trawl applied in the survey. Regional differences occur: Only sporadic catches are observed in the northern part of the German Wadden Sea, while more frequent ones occurred southwards and in the East Frisian Islands region. The obvious recent increase of abundance of Alosa fallax in spring allows for a lower ranking in the Red List of Endangered Species, while Allis shad (Alosa alosa) requires the same classification, as it was the never caught during the thirty years of surveys.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L. ) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil I: Allgemeiner Verlauf des jährlichen Reifeprozesses und der Laichaktivitäten in den verschiedenen Gebieten

From 1993 to 2003 special surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea. The ICES advice for cod in the Baltic Sea is based on yearly stock assessments of two separate stocks the western (SD 22 – 24) and the eastern stock (SD 25 – 32). Both stocks are characterized by different spawning seasons. The general progression of the maturity suggests that two types of development can be distinguished. In the western Baltic Sea (SD 22) the maturity development is temporal stable, with a relative short, main spawning period from March to April - spring spawner. In the Arkona Sea and Bornholm Basin the main spawning season starts in June and probably finishes in September - summer spawner. The proportion of spawners in summer is significantly higher than in spring in the Arkona Sea and Bornholm Basin. This again underlines the importance of the Arkona Sea for the reproduction success of the eastern Baltic cod stock. The analysis furthermore show, that the proportion of male spawners was significantly higher than the proportion of female spawners in all areas and the investigated months. This observation suggests that the reproductive success is only limited by the number of female cod which participates in the spawning process.

Die Reproduktion von Dorschen (Gadus morhua L. und Gadus morhua callarias L.) in der Ostsee unter besonderer Berücksichtigung der Arkonasee. Teil II: Statistische Analysen zum Anteil reproduktiv aktiver Dorsche in Bezug auf gebietsspezifische Unterschiede und Gemeinsamkeiten, sowie deren mögliche Ursachen.

Surveys were conducted to analyse temporal and spatial aspects of the spawning activities of cod in the Baltic Sea from 1993 to 2003. Part I of the article describes the general maturity development and the spawning activities in the western Baltic Sea, the Arkona Sea and the Bornholm Sea. The studies suggest that two types of spawner can be distinguished, the spring spawner in the western Baltic Sea and the summer spawner in the Arkona Sea and the Bornholm Basin. The descriptive analysis is supported by statistical studies presented in this article. It is shown, that the proportion of spawning individuals is significantly higher in summer than in spring in the ArkonaSea and the Bornholm Sea. Furthermore, it is shown that reproductive mixing of both types of spawner is possible in the Arkona Sea in May/June due to the hydrographical conditions in the Arkona Sea which were suitable in 8 of 10 years for successful reproduction of both Baltic cod stocks, and that spatial expansion of spawning activities of the eastern Baltic cod stock into the Arkona Sea is positive correlated with the size of spawning stock in the Bornholm Sea.

Wirkungsbezogene Detektion von toxischen Substanzen in Fisch und Umwelt

The detection of unknown and the quantification of known toxic substances is a challenge for the modern chemical and biological analysis. Effect-related in vitro methods, e.g. AH-receptor or estrogene-receptor mediated, offer some advantages compared to the classical chemical analysis. It could be shown that two cell lines exhibit different sensitivities to 2,3,7,8-tetrachlorodibenzodioxin (TCDD), although the cells contain the identical dioxin-receptor. The application and limitations of these methods in envi-ronmental analysis are discussed.

Horizontale Trennblätter in Trawls zur Verringerung von Discards in der Ostsee

A primary objective of the Common Fishery Policy of the European Union is the reduction of discards and unwanted by-catches in the fishery. In principle this could be achieved if the catching methods were optimised for this. Still high numbers of undersized flatfish are caught in the bottom trawls. Although EU regulations make the use of the BACOMA codend mandatory in the Baltic Sea cod areable to escape through square mesh escape window of the BACOMA net the whereas flatfish still remain in the cod-end. Gear experiments have been carried out with the aim to better separate cod from the flatfish fraction already when entering the rear belly, making use of the natural behaviour of the fish, i. e. the preferred swimming distance from the bottom of the net in the funnel. As cod have a natural tendency to keep a relativly great distance from the bottom, flatfish tend to stay close to it. It was attempted to separate both fractions by splitting the funnel into an upper and lower part with a horizontal panel. This wastested for two different nets, a cod trawl to separate cod from flatfish, and an eel-trawl to separate cod and flatfish from eel. Cod and flatfish separation is best at a panel distance of 50 cm from the bottom. Thus, 74 % of the cod were found in the upper panel, whereas 75 % of the flounder were in the lower section. A separation of eel from cod was however not possible, since eel tend to rise to the upper part of the net, together with cod.

Die Anwendung molekulargenetischer Verfahren in der fischereiwissenschaftlichen Forschung - Trennung von Fischpopulationen

The discrimination of stocks and separate reproductive units within fish species to facilitate fisheries management based on biological data has always been a challenge to fisheries biologists. We describe the use of three different molecular genetic techniques to detect genetic differences between stocks and closely related species. Direct sequencing of the mitochondrial ND3 gene describes the relationship between different aquaculture strains and natural populations of rainbow trout and revealed genetic homogeneity within the hatchery strains. Microsatellite analyses were used to explore the differences between redfish species from the genus Sebastes and to verify populations structure within S. mentella and S. marinus. This lead to an un equivocal discrimination of the species and an indication of populations structure within those species in the North Atlantic. The Amplified Fragment Length Polymorphisum (AFLP) methodology revealed genetic differences between Baltic and North Sea dap (Limanda limanda)and a possible population structure within the North Sea.

Der PAH-Metabolit 1-Hydroxypyren in der Galle von Klieschen (Limanda limanda) aus Nord- und Ostsee

Due to their carcinogenic properties, polycyclic aromatic hydrocarbons (PAH) are important environmental contaminants which may lead to increased levels of neoplastic aberrations in fish liver. To measure the PAH contamination of fish, concentrations of PAH metabolites were determined in the bile. The main metabolite 1-hydroxypyrene was determined in concentrations from < 0.8 to 189 ng/ml in bile of dab caught in the North Sea and the Baltic Sea re-spectively. The concentrations are comparable to levels of 1-hydroxypyrene measured in cod and herring from the Baltic Sea. The highest concentrations in dab bile were measured in fish from the inner German Bight and the Kiel Bight.

Die Qualitäts-Index-Methode (QIM), ein verlässliches Instrument zur sensorischen Bewertung der Frische von Fisch

Fish research institutes in Europe have made considerable effort in developing rapid, objective sensory methods for evaluation of fish freshness. The Quality Index Method(QIM) has been recommended for a European initiative regarding standardisation and harmonisation of sensory evaluation of fish. QIM-schemes have been developed for various common European fish species. Research has now provided the industry with a convenient, objective and powerful tool for measuring freshness of fish kept in ice Further research is needed to evaluate the applicability of QIM for fish handled, stored and processed under different conditions. However, for progress and development of QIM it is now very important that the fish sector implements QIM in fish auctions and the quality management system of the fish processing plants.

Einfluss von Reifung und technologischen Behandlungen auf die Proteine des Rogens von Regenbogenforellen (Oncorhynchus mykiss)

The use of differential scanning calorimetry for investigating the yolk proteins of the roe of rainbow trout allows to monitor the influence of maturation and vitellogenesis which modifies the DSC curves with regard to transition temperature and enthalpy. Two endothermic peaks become more and more pronounced with increasing maturation of the roe. However, it is still not known which protein fraction is represented by each of the peaks. DSC curves of yolk protein depend on fish species. They are also influenced by technological treatments. Further investigation is necessary to discover whether or not yolk proteins of other fish species are influenced in the same manner by maturation and vitellogenesis and which protein fraction represent the individual peaks.

Untersuchungen zur Aufzucht von Barramundi

Lates calcarifer (Barramundi) ist ein naher Verwandter des bei uns inzwischen seit Jahren bekannten und auf vielen Wochenmärkten zu findenden Viktoriabarsches(Lates niloticus), dem er auch im Aussehen ähnelt. Das Verbreitungsgebiet dieses euryhalinen Fisches sind die Küstenregionen mitsamt ihren Flußgebietssystemen des nördlichen Indischen und des westlichen tropischen Pazifischen Ozeans. Bei einer derartigen weiten Verbreitung ist es nicht verwunderlich, daß sich viele Bestände ausgebildet haben, die durchaus unterschiedliche Leistungen z. B. in Hinblick auf die Reproduktionsbiologie zeigen.

ICES-Arbeitsgruppentreffen zum "Lebenszyklus und Fischerei von Nordseegarnelen" (WGCRAN)

Two years after their last meeting, scientists from North Sea neighbouring countries working on aspects of brown shrimp biology and fisheries gathered in Oostende, Belgium, to exchange information and results of their research. The group was established ten years ago by the International Council of the Exploration of the Sea (ICES)during the Warnemünde Annual Science Conference. Data on brown shrimp landings, fishing effort and resulting landings per unit effort were compiled. For the first time a computer model was demonstrated simulating the life cycle of C. crangon on basis of experimental and field data available. It will provide a means for testing different possible scenarios and their effect on the brown shrimp stocks. Catch predictions are not possible by this, as no stock assessments can yet be achieved for brown shrimp, and a number of topics have to be addressed by further research programmes. However, an approach of estimating the level of landings on basis of preceding climatological and hydrographical data seemed promising. Furthermore selectivity experiments and electric gear types were reported giving reason to assume, that progress is possible in the further reduction of bycatches. The assembling of already existing data in various countries and their evaluation was recommended besides the pursuing of the mentioned fields of research and proper reporting of EU log book data by all countries.

Test von Fanggeräten zur Untersuchung von Grundfischfaunen in Windparkgebieten der Ostsee

With respect to future environmental impact assessment different bottom trawls are presently investigated for their suitability for sampling the fish fauna in potential windpark areas asses. For this purpose the international Baltic Sea Trawl, the Box trawl, two different small beam trawls and small eel fykes were compared on a research cutter in June 2002. The best catchability with the highest abundance of demersal fish species and widest length distribution was obtained with the Box trawl. During another cruise in December 2002 the Box trawl was again compared with the Windpark trawl. As a result the Box trawl performed best, with regard to the overall catchability. However the Windpark Trawl is easier to handle under the conditions onboard small fishing cutters.