Technische Empfehlungen für den künftigen Einsatz von Plattfischsteerten in der Ostsee

Die Grundschleppnetzfischerei in der Ostsee konzentriert sich im wesentlichen auf den Fang von Dorsch- und Plattfisch. Neben der Dorschfischerei gibt es auch beim Fang von Plattfisch gebiets- und zeitweise erhebliche Beifänge an untermaßigen Fischen, die verworfen werden müssen. Für beide in Form und Verhalten sehr unterschiedlichen Fischarten können bis dato die gleichen Steerte eingesetzt werden. Um die durch diese Mix-Fischerei an der südlichen Ostseeküste gegebenen Probleme zu verdeutlichen und auf eine zukünftig differenzierte Behandlung für die technischen Maßnahmen zur Verbesserung der Selektivität hinzuwirken, werden seit 1998 vergleichende Untersuchungen mit Schleppnetzsteerten unterschiedlicher Konstruktion durchgeführt.

Die Anteile von Sieb- und Futtergarnelen in deutschen Garnelenfängen im Jahre 2000

The German shrimp fisheries land different types of pro-duce. Besides cooked shrimp for human consumption small (undersized), raw shrimp (industrial shrimp) are landed regionally in the second half of each year for animal feedstuff purposes. They are dried in special plants and form sellable secession from sieving processes aboard shrimping vessels. Grading the cooked shrimp ashore gives the non-marketable fraction of too small shrimp, which is not meant for shelling. That fraction is produced all year alongside landings of shrimp and is used for feed-stuff as well. Both extra fractions are listed in the official statistics since 2000 for the first time. That year industrial shrimp made up 6 % of the total landings while the non-marketable, small cooked shrimp summed up to 7 %, respectively. Though being essential for specialised animal feeds they are commercially of very little value, making up to hardly 2 ‰ of the total turnover of the German shrimp fisheries.

Sensibilität von Seefischen an Bord. Teil 3: Untersuchungen an demersalen Fischarten der Barentssee

In previous papers the sensibility of pelagic and demersal fishes caught at depth of up to 80 m was reported. This paper deals with the sensitiveness of flatfishes, gadids, and redfish caught at depth between 260 and 450 m and with trawling times between 1 and 6 h. The sensitiveness of the fishes was tested according to the method described in previous publications (Münkner et. al. 1998) after 10 min keeping in running sea water and after 1h bulk storage respectively. The sensitiveness of the fishes increased from cod to saithe to haddock. Surprisingly American plaice and Greenland halibut turned out to be very sensitive, far more sensitive than plaice and dab caught at lower depths in the North Sea. This was indicated by the high amount of animals showing rigor already after a trawling time of 2 hand 10 min of keeping in seawater. After 1 h of bulk storage and increasing trawling time sensitiveness of all fishes decreased, as expected, significantly. Besides mechanical encroachments the main problem for the fishes caught at greater depths was the gas supersaturation in the blood and tissue causing blockage of the gill capillary vessels, exophthalmus, visible gas bubbles in the skin and eyes, and in some cases protusion of the intestines through the snout due to rapid dilatation of the swimbladder.

Winterfischerei auf Garnelen. Die Anteile der europäischen Garnelenflotten an den Anlandungen von Crangon crangon im Zeitraum Januar bis März der Jahre 1990 bis 1999

„Winter fishery“ on brown shrimp does not imply a special type of fishery. It merely means the continuation of the standard fishing procedure of parts of the fleet during wintertime, when the majority of the mostly smaller vessels stay in harbour due to generally unfavourable weather conditions for their activity. During 1990 to 1999 mean European wide landings in January and February summedup to 854 tonnes making up to only 4 % of the mean annual landings (21 805 t). While German vessels landed0.7 % (68.7 t) of their mean annual landings during that period, the other countries caught about 7 % of their individual, mean annual landings at the same time. The Netherlands and Denmark contributed highest tonnages of 580and 110 tonnes, respectively, to the total European landings, making up 81 % of them. As about 70 % of brown shrimp may carry eggs in January, the winter fishery took a mean total of about 2.15 x 1012brown shrimp eggs out of the stocks in that period annually. As there is no reliable assessment available concerning the brown shrimp stocks, it is despite of these high losses of eggs not possible to trace a negative effect of the winter fishery in scientific terms. However, precautional catch reductions in winter would be in favour of higher survival rates of eggs, which are the carrying source for the recruitment of brown shrimp stocks and catches in forthcoming summer and autumn seasons according to Dutch investigations.

Zum Stellenwert von Fischmehl in der Aquakultur

The worldwide aquaculture production amounts to about one third of the world fishery catch. While the world fishery catch in the last years is stagnating and an increase is not to be expected, the aquaculture rose by about 10 % annually. This rate of growth is also predicted for the next years. Fish meal and oil forms a key position for the further development of aquaculture, specially for carnivorous fish species, of which the salmonids will gain an increasing economic importance, not only on the European, but also on the Japanese and American markets. Without an adequate supply of fish meal and oil for the production of these fish species, the expected product quality cannot be realized under economic conditions. Fish meal and oil are commonly produced from small pelagic fish species, which, at present and in the near future, have no importance for direct human consumption. Since December2000 the use of fish meal and oil in Germany is only allowed for use in aquaculture and petfood. However, conclusive arguments for a ban on the utilization for other animal feeds do not exist so far. The European Union continues to allows feeding of other animals – except ruminants – with fish meal under certain control measures.

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.

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.

Fischereiliche Eignung von Dorsch-Stellnetzen mit Scheuchmaschen für den Schutz von Kleinwalen

The present contribution summarizes results of fishery investigations with standard cod gillnets and gillnets with attached large meshes of 3.4 meter meshsize built from rope of 6 mm diameter. Only the relative efficiency of both nets for cod was investigated. A reduction of 70 % of catch by the attached meshes was observed.

Anwendung von Fischzellkulturen in der Meeresforschung

A large number of chemical pollutants can be found in the marine environment. So it is necessary to obtain informations about the toxic effects of this contaminant mixtures in general and especially on single cell level. We used an organic extract of a marine sediment from the North Sea to investigate its cyto- and genotoxicity with an in vitro system, the comet assay or single cell gel electrophoresis (SCGE). The comet assay can be applied for estimating genotoxic effects of chemicals on single cell level. First results confirm the sensitivity of this assay and its applicability in assessing genotoxic load in environmental samples. A permant cell line, the EPC (Ephithelioma papulosum cyprini) was used for the experiments. It was possible to demonstrate the suitability of this in vitro test system for assessing genotoxic and cytotoxic effects of marine sediment extracts on EPC cells.

Genauigkeit von Alterslesungen, ihre Standardisierung und Kalibrierung

Age reading by use of otoliths is one of the basic but also most essential elements in practical fish population dynamics. Unfortunately, many factors can influence the readings of a single reader. Erronous readings, however, have a consequential effect on the evaluation and prediction of the development of the fish stock under consideration. In order to master this problem and to reduce out the effect of those factors, it seems neccessary to standardize the whole process of age reading between collaborating readers. From a statistical point of view calibration techniques can be used to identify those factors and to correct the readings with respect to them. The current article presents an overview over the basic idea behind this, over how to balance out the existing deviations and how to correct the age readings.

Bearbeitung von Fangproben mit neuen elektronischen Messmethoden

For 10 years the Institute for Fishing Technology, Hamburg (IFH) has been carrying out experiments in the brown shrimp fishery with beam trawls aiming at a reduction of unwanted bycatches. When the tests were transferred to commercial fishery conditions the personnel effort and costs increased markedly. It became e.g. necessary to install a deep-freeze chain to make it possible to evaluate more samples in the laboratory. This again required to increase the number of technicians for measuring the fish and shrimp samples, but also made it necessary to perform this work in the most rational and time-saving way by applying modern electronic aids. Though all samples still have to be sorted by species and have to be weighed and measured the introduction of electronic aids, however, like electronic measuring board and computer-aided image processing system, all weight and length data are immediately and digitally recorded after processing. They are transferred via a network to a server PC which stores them into a purpose-designed database. This article describes the applicationof two electronic systems: the measuring board (FM 100, Fa. SCANTROL), iniated by a project in the Norwegian Institute for Fishing Technology, and a computer-aided image processing system, focussing on measuring shrimps in their naturally flexed shape, also developed in the Institute for Fishing Technology in close collaboration with the University of Duisburg. These electronic recording systems allow the consistent and reproducible record of data independent of the changing day-to-day personal form of the staff operating them. With the help of these systems the number of measurements the laboratory could be maximized to 250 000 per year. This made it possible to evaluate, in 1999, 525 catch samples from 75 commercial hauls taken during 15 days at sea. The time gain in measuring the samples is about one third of the time previously needed (i.e. one hour per sample). An additional advantage is the immediate availability of the digitally stored data which enables rapid analyses of all finished subexperiments. Both systems are applied today in several institutes of the Federal Research Centre. The image processing system is now the standard measuring method in an international research project.

Sensibilität von Seefischen an Bord. Teil 2: Demersale und pelagische Fischarten aus Schleppnetzfängen in der Nord- und Ostsee

The sensitiveness of different demersal and pelagic fish species of 70 hauls in the North and Baltic Sea in water depths of 60 to 250 m and 15 to 80 m, respectively, amount of catch of 100 to 3500 kg and trawling times of 0,5 to 6 h on board of the FRV “Walther Herwig III” was investigated. Some demersal fish species , e.g. saithe (Pollachius virens), were even still sensitive, when caught at a water depth of 250 m at a trawling time of 1,5 h. Generally the number of sensitive fishes was reduced with increasing water depth, amount of catch, trawling time and following storage of the catch on board. Among demersal fishes the species without swimbladder and flat fishes were clearly more resistent to mechanical stress. On the contrary, pelagic fish species were generally less robust. After trawling times of 2 h no sensitive animals were observed. In some fisheries there are mixed catches of demersal and pelagic fish species with different sensitiveness. In commercial fisheries, there is therefore – under animal welfare aspects – for the time being, no prospect for an improvement of the catching and slaughtering procedure on board

Qualitätsveränderung von rohen Fischfilets bei Kühlschrank-Lagerung

Raw fillets of saithe, red fish and salmon were stored over a period of 2 days at 6 to 9 °C before preparing by frying, deep-frying or cooking in a microwave oven. The raw and prepared fillets were tested for bacterial loads, TVBN (total volatile basic nitrogene) and for the sensorial status. It was shown that saithe and red fish started more rapidly to spoil under these conditions than salmon. The fillets showed growing bacterial populations and produced high amounts of TVBN. Sensory changes, especially in flavour and odour, took place but the scores kept in an acceptable range. The investigations indicated that it is possible to store raw fillets for 1 or even 2 days in refrigerator but due to the loss of quality it is recommended to use only really fresh fillets stored in very clean containers. It was further shown that it is very important to heat fillets sufficiently during cooking or frying in order to destroy all microorganisms and to obtain safe and stable meals.

Einfluss des Tag-Nacht-Verhaltens von Fischen auf das Ergebnis hydroakustischer Messungen

Echo integration is an established method for stock estimation. However, this method is not free of errors like every other measuring method. Especially the variation between day and night behaviour of fish may lead to large measuring errors. A new method is represented detecting such systematic errors, exemplified by investigations during the international hydroacoustic survey on the spring spawning herring in the Norwegian Sea. For this method all measured sA-values are sorted by starting time of the measuring unit distance. In order to reduce random influences a moving average over five time intervals is computed. When displaying these values in a diagram makes it is very easy to detect systematic errors based on the differences in day-night behaviour. For both species, herring and blue whiting, stock estimations are calculated based on the measured sA-values and the results of the analysed trawl catches. The influence of the differnt day and night behaviour of herring on the results of its biomass estimation is rather low. For blue whiting the measured values were about three time higher during day time than during night time. The result of this investigation should initiate a change of the evaluation procedure for stock estimation based on hydroacoustic measurements.