Weitere Selektionsuntersuchungen an Schleppnetzsteerten für den Plattfischfang in der Ostsee

The presentation includes investigations and results regarding Baltic flatfish selectivity with different trawl codend constructions. These investigations were carried out 1999/ 2000 on board of FRV “Clupea” and a commercial 17 m cutter. As could be shown, both an enlarged mesh size and another mesh form than rhombic can improve the selectivity of these fish. As flatfish catches with trawls mostly also cover cod, this mixed fishery at the southern Baltic coast should in future be managed by differentiated technical regulations for an improved selectivity. The results, also based on UW observations, current measurements, and wind tunnel tests with models, demonstrate some possible technical solutions.

Die Lage der Fischbestände in Nordostatlantik, Nord- und Ostsee. Einschätzungen des Internationalen Rates für Meeresforschung im Frühjahr 2001

The spring session of ACFM gave advice for a number of stocks in the North Atlantic, North Sea and Baltic. The present assessment of the situation is given here for stocks of importance for the German fishery. These are: Blue Whiting: the stock size is rapidly decreasing due to high catches; ICES recommends a closure of the fishery. Herring (Atlanto-Scandian, Norwegian spring spawner): Stock is within save biological limits, weak recruitment of the recent years will lead to a further reduction of biomass. Herring (North Sea): revision of the assessment led to a different perception of the stock: SSB was in 2000 below Blim. Excellent recruitment will lead to an increase of SSB over Blim within this year, but ICES recommends to reduce fishing mortality on adults significantly. Herring (Baltic spring spawner in 22–24, IIIa): Still no increasing tendency is detectable. Herring (VIaNorth): stable. Redfish: generally further decreasing tendency observed, a reduction of the fishery is recommended. Signs of recovery visible only for two units. Greenland Halibut: State of the stock not quite clear, but slightly positive tendencies. The present fishing intensity should be reduced. Cod (Kattegat): Weak recruitment, outside safe biological limits. ICES recommends a closure of the fishery. Cod (22–24, Western Baltic): Stock situation unclear due to extensive migrations. F should be reduced by at least 10%.

Neue Chance für den Nordsee-Kabeljau

Während der 483. Reise von FFK “Solea“ (24.10. bis 9.11.01) wurde wie in jedem Herbst die Nachwuchssituation von Kabeljau in der Deutschen Bucht untersucht. Der dabei berechnete Index hat sich in seiner 20-jährigen Laufzeit als relativ verlässliches Maß für die Abschätzung der Stärke des jeweils jüngsten Jahrgangs erwiesen.

Saisonale und regionale Unterschiede zwischen den 0-Gruppen-Schollen-Discards in der deutschen Garnelenfischerei

Shrimping in the waddensea is frequently considered to significantly reduce the numbers of juvenile plaice . This investigation aims to reveal the seasonal and regional differences regarding discards in the German waddensea and sets the results in relation to the bycatch projects with German participation. Furthermore, methodological aspects are evaluated to find possible effects on the estimation of the netted numbers. The bycatch problem exists predominantly throughout the summer season, but high catches of juvenile plaice can occur occasionally in autumn. The discard issue seems to be most important in the East Frisian region, while the Elbe and Schleswig-Holstein areas are of lesser importance. Considering the distribution of the fish in the environment is as indispensable as sampling of the shrimp fleet with optimum representativity. There are indices that the contribution of the Dutch shrimp fleet to the discard mortality of juvenile plaice was underestimated in the recent past. A combination of time and area closures as restrictions in combination with the extensive application of selective gears could possibly gain the best protection for the affected species.

Die Bedeutung biologischer Daten aus der deutschen Seelachsfischerei für Bestandsabschätzung und Management

Since 1999, the ICES Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak assesses the saithe stock in the North Sea, Skagerrak and west of Scotland as a single stock unit. The sampling, evaluation and role of biological data from the German saithe fishery in the assessment are described. The German data showed similar trends as observed in French and Norwegian series. Based on these estimates, the spawning stock recovered to more than 200 000 t due to reductions in quotas and exploitation rates. Thus, the production of the stock increased also in combination with good recruitment and positive trends in spawning stock size and landings were projected for 2002. The biological data derived from the German saithe fishery dominated the assessment of stock size, structure and exploitation. This fact encourages a continuation of the described analyses based on sampling onboard fishing vessels and fish markets by the Institute for Sea Fisheries. The successful collaboration with the saithe fishing industry is judged as an important contribution to the sustainable management of fish stocks.

Gegenüberstellung von mathematisch-physikalischer Modellierung und Messungen an geschleppten fischereitechnischen Systemen

When drafting a new model of a towed technical system for fisheries (trawl, towed TV gear or similar), and also when measuring an existing and already tested system it is not easy to foresee of practical behaviour, which depends of various parameters. The measuring programme for recording all data needs a lot of time and money, and also has some limitations. Therefore we developed for such systems mathematical-physical models, which allow a complex calculation. Their real value, however, results only from practical verification. During the cruise no. 222 of “Walther Herwig III” in November 2000 comparative investigations for 2concrete systems were carried out. This was done in cooperation with the University in Rostock, where such models are being developed and computerized. One of the systems mesasured was a pelagic herring trawl and the other one the towed TV gear for underwater observations of the Institute for Fishery Technology and Fish Quality. The correspondence between model calculation and measurements was very high for both systems.

Vergleichende Eislagerung von ausgenommenen und unausgenommenen Schleien

New regulations of the German “Fisch-Hygiene-Verordnung” lay down that all fish except pelagic species have to be gutted immediately after catch or killing, especially fresh water fish from aquaculture. Only gutted fish should be sold to the consumer. At the present time, however, it is not unusual to sell ungutted fish like tropical or mediterranean species from foreign countries, even the EC area. In this investigation the influence of gutting on the fish quality during storage on ice was tested in tench (Tinca tinca) as a model. Quality changes were controlled by sensory, chemical, physical and microbiological assessment. It was shown that for tench there were no differences between gutted and ungutted fish during 12 days of storage on ice.

31. Jahrestagung der "West European Fish Technologit´s Association" in Espoo, Finnland

Vom 27.-31. Mai 2001 fand in Espoo, Finnland, die 31. Jahrestagung der WEFTA (West European FishTechnologist’s Association) statt. 75 Teilnehmer aus15 europäischen Ländern, der FAO und der Europäischen Kommission sowie aus den USA und Kanadawaren der Einladung des VTT Biotechnology, eines großen finnischen Forschungsinstituts auf dem Gebiete der Biotechnologie und biologischer Materialien, zu dieser Tagung gefolgt. Die Durchführung in einemKongresszentrum in Espoo, nahe der finnische Hauptstadt Helsinki direkt am Bottnischen Meerbusen gelegen, ermöglichte einen straffen organisatorischen Ablauf und die Einhaltung des Zeitplanes der mit 41 Vorträgen und 18 Postern recht umfangreichen Veranstaltung, die in 7 Themenkomplexe gegliedert war. Nachfolgend werden wesentliche Ergebnisse der einzelnen Beiträge zusammengefasst

Lage und Entwicklung ausgewählter Fischbestände. Einschätzung des ICES im Oktober 2001

During the autumn session of the ICES Advisory Committee for Fisheries Management (ACFM) the stock of the Northern and Southern Shelfs, North Sea and Skagerrak have been analysed and assessed, as well as the mackerel and horse mackerel, sardine, anchovy, Pandalus and Eel. As in previous years ICES recommends a reduction in fishing mortality for a number of stocks. Moreover, ICES recommends for many stocks to establish recovery and management plans, to safeguard a continuous development of the stocks towards safe biological limits.

Neue Chance für den Nordsee-Kabeljau: Seevögel machen bereits im Sommer 2001 auf starken Jahrgang aufmerksam

Im Oktober/November des vergangenen Jahres ergab sich während der 483. Reise von FK „Solea“ ein im Vergleich zu den vier Vorjahren hoher Fangindex von 220 Kabeljau Gadus morhua je Stunde (Weber 2001). Die Fische hatten eine Länge von 15 bis18 cm und waren besonders in Küstennähe Ostfrieslands anzutreffen. Durch unsere Langzeituntersuchungen zur Ökologie der Flussseeschwalbe Sterna hirundo im Wattenmeer sind wir bereits im Juni des Jahres 2001 auf den starken Jahrgang des Kabeljaus aufmerksam geworden und können die Vermutung von Weber bestätigen, dass die Kabeljaus den Sommer über im Wattengebiet herangewachsen sind.

Schwacher Nachwuchsjahrgang 2001 des Herings in der westlichen Ostsee

Several fishery independent estimates of the year-class strength are necessary for the assessment and the management of the total fish stock. An index for the year-class strength of the spring spawning herring in the western Baltic Sea is estimated on the basis of larvae surveys in the most important spawning ground. The results indicate a weak year-class 2001.

Die Fruchtbarkeit von Dorschen in der Ostsee - was verrät sie uns?

About 1500 ovaries of Baltic cod were prepared for estimating the potential absolute and relative individual fecundity. The female cod were sampled in the Belt Sea, ICES Subdivision (SD) 22, in the Arkona Sea, SD 24, and in the Bornholm Sea, SD 25. The investigations started in1992 and until 1999 cruises were carried out to catch female cod in the different sub-divisions every year. The results shows that the potential fecundity is not a stable biological parameter, and that significant changes are possible within a relative short period. It was demonstrated that the developments of the potential individual fecundity of the western (Gadus morhua morhua) and eastern Baltic cod stocks (Gadus morhua callarias) were different. In contrast to the stable individual fecundity of the western cod the absolute and relative fecundity of the eastern repeat spawners increased from 1993 to 1999, significantly. The reason of this development seems to be the dramatic decrease of the eastern cod stock and the more successful reproduction of individuals that produce oocytes with a lower dry weight in combination with a higher relative fecundity.

Nährstoff-Einträge aus der deutschen Aquakultur in die Ostsee

Es gibt vier bzw. fünf große Gewässereinzugsgebiete mit Bedeutung für die Fischzucht. Dies sind die Donau mit ihrem Abfluß in das Schwarze Meer, Rhein, Weser und Elbe, die in die Nordsee entwässern sowie die Oder, die in die Ostsee mündet. Daneben gibt es noch einige weitere kleinere Flüsse von Nordwesten bis Nordosten Deutschlands, die in Nordsee (z. B. Eider, Stör) oder Ostsee (z. B. Stebnitz) fließen und das Ablaufwasser von Fischzuchten transportieren können.

Ostseedorschselektion - bestehende und vorgesehene neue technische Maßnahmen

Since the beginning of the nineties the situation of the Baltic cod stock is deteriorating constantly. The fishery administration (International Baltic Sea Fisheries Commission) tries to counter this by issuing new technical measures. Existing measures (raise of mesh opening from 105 to 120 mm, “Danish” and “Swedish” escape windows) and newly introduced technical measures (BACOMA codend and raise of the mesh opening in conventional codends to 130 mm) show a number of deficiencies putting their efficiency in doubt. Available well tested alternatives to the newly introduced measures without their negative side effects (codends made of netting turned by 90°, and other designs) are presently left out of regard. Models of socioeconomic effects are likewise ignored.

Biologische Veränderungen im Versenkungsgebiet für schwach radioaktive Abfälle im Iberischen Tiefseebecken?

From 1979 to 2000, the site for the dumping of low-level radioactive wastes and an unaffected site in the North-east Atlantic were investigated to determine the biomass data of the benthopelagic nekton and the benthic organisms. The investigation shall demonstrate the influence on the biocoenosis of the so-called "artificial reef effect", caused by dumped waste drums. For sampling benthopelagic and benthic organisms, we used a modified Agassiz trawl, called the Deep-sea Closing Net. With the exception of the “Amperima event” in 1996 – a unique occurrence of a large number of sea-cucumbers – there was no change in the composition of benthopelagic and benthic organisms through the years. The biomass of the benthopelagic nekton was characterized by Macrouridae(rat-tailed fishes) and the main tax on of the benthos was Actiniaria (sea-anemones).